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Tech Bally 2518-32 Sound Board
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The Hammer
Jun 2, 2013, 7:08:04 PM6/2/13
to
I have my first pin with the -32 sound board - SMDM.
How loud is that board supposed to get?
I have the volume all the way up and I can hear it, but it is drowned out
pretty easily.
+12 and +5 are OK.
I replaced the electrolytic caps. I also replaced U10 - LM380.
There is no hum. Speaker seems to be fine, no distortion. Pot seems to
work.
Suggestions?
How loud is that board supposed to get?
I have the volume all the way up and I can hear it, but it is drowned out
pretty easily.
+12 and +5 are OK.
I replaced the electrolytic caps. I also replaced U10 - LM380.
There is no hum. Speaker seems to be fine, no distortion. Pot seems to
work.
Suggestions?
The Hammer
Jun 2, 2013, 7:55:53 PM6/2/13
to
in article CDD11E64.3E448%LHNew...@frontier.com, The Hammer at
LHNew...@frontier.com wrote on 6/2/13 4:08 PM:
I am devolving into the shotgun approach.
I read on Pinwiki that U9 LM741 should have +2 VDC at pin 2. It did not.
So I replaced it.
No change. Still low volume.
LHNew...@frontier.com wrote on 6/2/13 4:08 PM:
I read on Pinwiki that U9 LM741 should have +2 VDC at pin 2. It did not.
So I replaced it.
No change. Still low volume.
barakandl
Jun 2, 2013, 9:47:21 PM6/2/13
to
Sound output goes from a 4049 at U8, To the OP amp u replaced then the other amp is lm380n. Suppose the other amp could be weak.
These boards are very picky about grounding. I would try isolating its ground from the back box ground and see if you get different results.
barakandl
Jun 2, 2013, 9:49:17 PM6/2/13
to
GPE
Jun 3, 2013, 1:29:30 AM6/3/13
to
"The Hammer" wrote in message
news:CDD11E64.3E448%LHNew...@frontier.com...
Replaced *all* electrolytics?
The problematic ones are often the small 1 and 2uF caps -- the DC blocking,
coupling caps. These going bad can cause a loss in volume.
The Hammer
Jun 3, 2013, 3:13:36 PM6/3/13
to
in article fNSdndjklIYrtDHM...@giganews.com, GPE at
GPE_NoSp...@cox.net wrote on 6/2/13 10:29 PM:
Thanks Ed. I ordered from you all electrolytics on that board. I put new 1
uF caps in C8 and C11. 2.2 uF in C6. 100 uF in C13. And 100 uF 100V in
C17.
I replaced those first, tested, and there was no change in volume. Then I
replaced U10 LM380 and tested. Then U9 LM741 with no change. I forgot to
add that I do have +2 VDC at pin 2 on U9.
It is not a perfect test, but the speaker measures ~7 ohms resistance, so
the continuity is good. I also measured that across the pins on the back of
the PCB with the speaker connected, so the connectors are good.
The volume pot measures 9.1 k and it is turned all the way up and measures ~
zero ohms to the center from the high side, so it is acting as it should.
I can hear all the tones. It is just not loud.
I guess I am going to have to rip out a spare speaker from somewhere to test
it for certain.
There is no noise when I adjust the pot, so I just have to suspect that part
of the circuit. I just do not believe that adjusting the 30 year old pot
would be totally quiet. My suspect is C9 (blocking the signal) or C10
leaking from the + to the - side.
Anyone know why pin 6 of LM380 is not grounded? The only time I have seen
that cap used is some kind of frequency correction like in a phono input.
GPE_NoSp...@cox.net wrote on 6/2/13 10:29 PM:
uF caps in C8 and C11. 2.2 uF in C6. 100 uF in C13. And 100 uF 100V in
C17.
I replaced those first, tested, and there was no change in volume. Then I
replaced U10 LM380 and tested. Then U9 LM741 with no change. I forgot to
add that I do have +2 VDC at pin 2 on U9.
It is not a perfect test, but the speaker measures ~7 ohms resistance, so
the continuity is good. I also measured that across the pins on the back of
the PCB with the speaker connected, so the connectors are good.
The volume pot measures 9.1 k and it is turned all the way up and measures ~
zero ohms to the center from the high side, so it is acting as it should.
I can hear all the tones. It is just not loud.
I guess I am going to have to rip out a spare speaker from somewhere to test
it for certain.
There is no noise when I adjust the pot, so I just have to suspect that part
of the circuit. I just do not believe that adjusting the 30 year old pot
would be totally quiet. My suspect is C9 (blocking the signal) or C10
leaking from the + to the - side.
Anyone know why pin 6 of LM380 is not grounded? The only time I have seen
that cap used is some kind of frequency correction like in a phono input.
The Hammer
Jun 3, 2013, 3:17:43 PM6/3/13
to
in article 5ca29c87-d207-4a9f...@googlegroups.com, barakandl
at bara...@gmail.com wrote on 6/2/13 6:47 PM:
> On Sunday, June 2, 2013 7:55:53 PM UTC-4, The Hammer wrote:
>
>
> These boards are very picky about grounding. I would try isolating its ground
> from the back box ground and see if you get different results.
Based on your post, I tried the board while not attached to the back box,
> These boards are very picky about grounding. I would try isolating its ground
> from the back box ground and see if you get different results.
with no change.
I cannot prove the speaker is good, but it tests at 7 ohms and does not
sound distorted. I do not have a spare handy, but will have to figure
something out to run to another one just to discount the speaker as a
factor. Maybe rip one out of my Silverball Mania. I think hooking it up to
my bookshelf speaker is not a good test.
:-)
Might just be easier to hook up my scope.
The Hammer
Jun 9, 2013, 7:26:17 PM6/9/13
to
in article fNSdndjklIYrtDHM...@giganews.com, GPE at
GPE_NoSp...@cox.net wrote on 6/2/13 10:29 PM:
>
>
GPE_NoSp...@cox.net wrote on 6/2/13 10:29 PM:
>
>
Review: I replace the electrolytics, U9 LM741 and U10 - LM380. I even tried
a second U9. The volume control and sustain controls are good. I tried a
second speaker.
I pulled out the scope and looked at the waveforms.
I appear to get the 11v waveform at CR1 & CR2. I also appear to get the
waveforms specified on either side of R2.
I figured it might be one of the caps blocking the signal. Either side of
C9 seem to be the same between U10 and U9, but it seems to be very low. I
checked C10 in case it was shorted. I see the audio on pin 2 of U10 and do
not see it at pin 6 so C10 is good. If this helps at all, I get hum when I
check pin 6 with the scope, but no extra noise when I check pin 2.
U10 seems to be working in that the very weak signal coming out of pin 8 is
bigger than that going in at pin 2.
Since the signal going into U10 is very low, I am looking at U9. R17 is
good. Pins 3 & 4 are grounded. I have +12 at pin 7. I tried a second U9.
I am lost as to what is supposed to happen up with the signal from U11. It
is strong at the top of R5, but mostly gone on the other side, which it
should be because of the R5 (10k) and R15 (360) values.
And what is U8 supposed to do with no Vcc or Vss connection?
I cannot confirm that R11 is good at 1 megaohm because with R10 and R13 in
the circuit, I read ~200K.
GPE
Jun 9, 2013, 7:58:05 PM6/9/13
to
"The Hammer" wrote in message
I got back to working on this.
Review: I replace the electrolytics, U9 LM741 and U10 - LM380. I even tried
a second U9. The volume control and sustain controls are good. I tried a
second speaker.
I pulled out the scope and looked at the waveforms.
I appear to get the 11v waveform at CR1 & CR2. I also appear to get the
waveforms specified on either side of R2.
I figured it might be one of the caps blocking the signal. Either side of
C9 seem to be the same between U10 and U9, but it seems to be very low. I
checked C10 in case it was shorted. I see the audio on pin 2 of U10 and do
not see it at pin 6 so C10 is good. If this helps at all, I get hum when I
check pin 6 with the scope, but no extra noise when I check pin 2.
U10 seems to be working in that the very weak signal coming out of pin 8 is
bigger than that going in at pin 2.
Since the signal going into U10 is very low, I am looking at U9. R17 is
good. Pins 3 & 4 are grounded. I have +12 at pin 7. I tried a second U9.
I am lost as to what is supposed to happen up with the signal from U11. It
is strong at the top of R5, but mostly gone on the other side, which it
should be because of the R5 (10k) and R15 (360) values.
And what is U8 supposed to do with no Vcc or Vss connection?
I cannot confirm that R11 is good at 1 megaohm because with R10 and R13 in
the circuit, I read ~200K.
U8 -- they don't really use this as an IC, they only use some of the
MOSFET's within the IC.
But in order for this to work - this part must have the "U" within the
suffix. Does it?
Ed
The Hammer
Jun 9, 2013, 10:32:39 PM6/9/13
to
in article gpWdndTG8q8WiyjM...@giganews.com, GPE at
GPE_NoSp...@cox.net wrote on 6/9/13 4:58 PM:
I am sorry Ed. You lost me on this one.
The IC (which is the original) says "620-33" and "G7823" or "Q7823" on it.
I am not certain of the first letter being a G or a Q.
In the manual, it is identified as "E620-33" or "E820-33". It is darn
difficult to tell and 8 from a 6.
GPE_NoSp...@cox.net wrote on 6/9/13 4:58 PM:
The IC (which is the original) says "620-33" and "G7823" or "Q7823" on it.
I am not certain of the first letter being a G or a Q.
In the manual, it is identified as "E620-33" or "E820-33". It is darn
difficult to tell and 8 from a 6.
GPE
Jun 10, 2013, 12:48:00 AM6/10/13
to
"The Hammer" wrote in message
The E620-33 is a Bally part number. 7823 means the part was made in 23rd
week of 1978. You have the correct part... which is a 4000 series CMOS part
that is not known for being real 'robust'.
Generic part number for U8 is a 4049 - typically used as a hex inverter (six
inverters in one IC). This inversion is accomplished using several MOSFET
type transistors within the device. Bally did something strange with this
one - rather than use the part as an inverter - they are using the MOSFET
type transistors within the IC as part of their sound circuit. This is why
there is no +5V or ground connection at the proper pins on this IC -- in
fact, the normal power and ground pins for this IC are actually used as
outputs from the IC. This little slight of hand caught quite a few people
off guard.
If replacing with new parts - you would replace it with a 4049UB instead of
a 4049B. The "U" means the outputs are unbuffered -- this allows direct
access to the MOSFET transistors within the part.
Ed
barakandl
Jun 10, 2013, 8:24:08 AM6/10/13
to
On Jun 10, 12:48 am, "GPE" <GPE_NoSpamPle...@cox.net> wrote:
> "The Hammer" wrote in message
>
> news:CDDA88D7.407E5%LHNew...@frontier.com...
>
> in article gpWdndTG8q8WiyjMnZ2dnUVZ_rqdn...@giganews.com, GPE at
> "The Hammer" wrote in message
>
> news:CDDA88D7.407E5%LHNew...@frontier.com...
>
> GPE_NoSpamPle...@cox.net wrote on 6/9/13 4:58 PM:
> > ---------------------------------------
>
> > U8 -- they don't really use this as an IC, they only use some of the
> > MOSFET's within the IC.
> > But in order for this to work - this part must have the "U" within the
> > suffix. Does it?
>
> > Ed
>
> I am sorry Ed. You lost me on this one.
>
> The IC (which is the original) says "620-33" and "G7823" or "Q7823" on it.
> I am not certain of the first letter being a G or a Q.
>
> In the manual, it is identified as "E620-33" or "E820-33". It is darn
> difficult to tell and 8 from a 6.
>
> ------------------------------------------------------------------------------------------------------------
>
> > U8 -- they don't really use this as an IC, they only use some of the
> > MOSFET's within the IC.
> > But in order for this to work - this part must have the "U" within the
> > suffix. Does it?
>
> > Ed
>
> I am sorry Ed. You lost me on this one.
>
> The IC (which is the original) says "620-33" and "G7823" or "Q7823" on it.
> I am not certain of the first letter being a G or a Q.
>
> In the manual, it is identified as "E620-33" or "E820-33". It is darn
> difficult to tell and 8 from a 6.
>
>
> The E620-33 is a Bally part number. 7823 means the part was made in 23rd
> week of 1978. You have the correct part... which is a 4000 series CMOS part
> that is not known for being real 'robust'.
>
> Generic part number for U8 is a 4049 - typically used as a hex inverter (six
> inverters in one IC). This inversion is accomplished using several MOSFET
> type transistors within the device. Bally did something strange with this
> one - rather than use the part as an inverter - they are using the MOSFET
> type transistors within the IC as part of their sound circuit. This is why
> there is no +5V or ground connection at the proper pins on this IC -- in
> fact, the normal power and ground pins for this IC are actually used as
> outputs from the IC. This little slight of hand caught quite a few people
> off guard.
>
> If replacing with new parts - you would replace it with a 4049UB instead of
> a 4049B. The "U" means the outputs are unbuffered -- this allows direct
> access to the MOSFET transistors within the part.
>
> Ed- Hide quoted text -
> The E620-33 is a Bally part number. 7823 means the part was made in 23rd
> week of 1978. You have the correct part... which is a 4000 series CMOS part
> that is not known for being real 'robust'.
>
> Generic part number for U8 is a 4049 - typically used as a hex inverter (six
> inverters in one IC). This inversion is accomplished using several MOSFET
> type transistors within the device. Bally did something strange with this
> one - rather than use the part as an inverter - they are using the MOSFET
> type transistors within the IC as part of their sound circuit. This is why
> there is no +5V or ground connection at the proper pins on this IC -- in
> fact, the normal power and ground pins for this IC are actually used as
> outputs from the IC. This little slight of hand caught quite a few people
> off guard.
>
> If replacing with new parts - you would replace it with a 4049UB instead of
> a 4049B. The "U" means the outputs are unbuffered -- this allows direct
> access to the MOSFET transistors within the part.
>
>
> - Show quoted text -
Great post Ed.
The Hammer
Jun 10, 2013, 9:22:43 PM6/10/13
to
in article cumdnfvzsu3jxyjM...@giganews.com, GPE at
GPE_NoSp...@cox.net wrote on 6/9/13 9:48 PM:
>
> "The Hammer" wrote in message
> news:CDDA88D7.407E5%LHNew...@frontier.com...
>
> in article gpWdndTG8q8WiyjM...@giganews.com, GPE at
> GPE_NoSp...@cox.net wrote on 6/9/13 4:58 PM:
>
>> And what is U8 supposed to do with no Vcc or Vss connection?
>>
>>
>>
----------------------------------------------------------------------------->>
>>
>>
>>
for learning. In looking at the datasheet for 4049, that is quite an odd
trick that Bally did.
I happen to have a couple of spare 4049UBE that I got from another guy named
Ed - is that a coincidence or what! - that I will slap in and see if this
fixes the problem.
The Hammer
Jun 10, 2013, 10:58:57 PM6/10/13
to
in article CDDBC9F3.40AA3%LHNew...@frontier.com, The Hammer at
LHNew...@frontier.com wrote on 6/10/13 6:22 PM:
>
>
>
> in article cumdnfvzsu3jxyjM...@giganews.com, GPE at
> GPE_NoSp...@cox.net wrote on 6/9/13 9:48 PM:
>
>>
>> "The Hammer" wrote in message
>> news:CDDA88D7.407E5%LHNew...@frontier.com...
>>
>> in article gpWdndTG8q8WiyjM...@giganews.com, GPE at
>> GPE_NoSp...@cox.net wrote on 6/9/13 4:58 PM:
>>
>
>>> And what is U8 supposed to do with no Vcc or Vss connection?
>>>
>>>
>>>
----------------------------------------------------------------------------
I am bummed. Nope, it did not fix it. All the sounds are there, but they
are not at the level that they can be heard in a noisy room. There is some
buzz while the lights are being powered on.
Three IC's replaced and no luck. This is embarrassing. I have never had to
replace this many IC's in a board before. I must have missed something.
One of my measurements must be wrong or I misinterpreted something. This is
the only Bally pin I have that uses this era board.
It was interesting to see that the entire top row of that IC is unused. I
use inline machine pin sockets and I did not even bother putting an entire
one in on the top for pins 9 - 16.
LHNew...@frontier.com wrote on 6/10/13 6:22 PM:
>
>
>
> in article cumdnfvzsu3jxyjM...@giganews.com, GPE at
> GPE_NoSp...@cox.net wrote on 6/9/13 9:48 PM:
>
>>
>> "The Hammer" wrote in message
>> news:CDDA88D7.407E5%LHNew...@frontier.com...
>>
>> in article gpWdndTG8q8WiyjM...@giganews.com, GPE at
>> GPE_NoSp...@cox.net wrote on 6/9/13 4:58 PM:
>>
>
>>> And what is U8 supposed to do with no Vcc or Vss connection?
>>>
>>>
>>>
----------------------------------------------------------------------------
are not at the level that they can be heard in a noisy room. There is some
buzz while the lights are being powered on.
Three IC's replaced and no luck. This is embarrassing. I have never had to
replace this many IC's in a board before. I must have missed something.
One of my measurements must be wrong or I misinterpreted something. This is
the only Bally pin I have that uses this era board.
It was interesting to see that the entire top row of that IC is unused. I
use inline machine pin sockets and I did not even bother putting an entire
one in on the top for pins 9 - 16.
The Hammer
Jun 11, 2013, 12:14:02 AM6/11/13
to
I am totally missing something easy here.
It works exactly the same with U9 removed. That means all of my signal is
coming through R17.
I have replaced U9 with a new LM741CN. I tried a second one.
I have confirmed that pin 7 has +12VDC, while U9 is installed.
Pins 1, 5 & 8 are not connected.
When I install U9, I get +2 VDC on the + side of C8. Note that C8 is a 1 uF
electrolytic, which is not clear on the diagram.
When U9 is removed, I do not get any VDC on C8. So that is connected.
I am missing something here. Don't tell me that both LM741CN are defective.
Not buying that.
It works exactly the same with U9 removed. That means all of my signal is
coming through R17.
I have replaced U9 with a new LM741CN. I tried a second one.
I have confirmed that pin 7 has +12VDC, while U9 is installed.
Pins 3 & 4 are grounded.
When I touch pin 6, I get a loud buzz, so it is connected to U10.
Pins 1, 5 & 8 are not connected.
When I install U9, I get +2 VDC on the + side of C8. Note that C8 is a 1 uF
electrolytic, which is not clear on the diagram.
When U9 is removed, I do not get any VDC on C8. So that is connected.
I am missing something here. Don't tell me that both LM741CN are defective.
Not buying that.
GPE
Jun 11, 2013, 12:54:35 AM6/11/13
to
"The Hammer" wrote in message
Doubtful. Check R37, R38 and C23. Broken trace?
Ed
wayout440
Jun 11, 2013, 10:45:13 AM6/11/13
to
The Hammer;2081031 Wrote:
> in article CDDBC9F3.40AA3%LHNewsgroup (AT) frontier (DOT) com, The
> Hammer at
> LHNewsgroup (AT) frontier (DOT) com wrote on 6/10/13 6:22 PM:
>
> >
> >
> >
> > in article cumdnfvzsu3jxyjMnZ2dnUVZ_uidnZ2d (AT) giganews (DOT) com,
> GPE at
> > GPE_NoSpamPlease (AT) cox (DOT) net wrote on 6/9/13 9:48 PM:
> >
> >>
> >> "The Hammer" wrote in message
> >> news:CDDA88D7.407E5%LHNewsgroup (AT) frontier (DOT) com...
> >>
> >> "The Hammer" wrote in message
> >>
> >> in article gpWdndTG8q8WiyjMnZ2dnUVZ_rqdnZ2d (AT) giganews (DOT) com,
> GPE at
> >> GPE_NoSpamPlease (AT) cox (DOT) net wrote on 6/9/13 4:58 PM:
looking in the wrong place?
--
wayout440
This USENET post sent from http://rgparchive.com
The Hammer
Jun 11, 2013, 2:35:11 PM6/11/13
to
in article wayout44...@rrgparchive.com, wayout440 at
wayo...@gmail.com wrote on 6/11/13 7:45 AM:
>
> What makes you certain that the board is the problem - perhaps you are
> looking in the wrong place?
>
I am open to suggestions.
I tried a different speaker.
Power to the board is good.
It is being triggered by the CPU as it makes tones. If it were dead silent,
I might suspect otherwise.
wayo...@gmail.com wrote on 6/11/13 7:45 AM:
>
> What makes you certain that the board is the problem - perhaps you are
> looking in the wrong place?
>
I tried a different speaker.
Power to the board is good.
It is being triggered by the CPU as it makes tones. If it were dead silent,
I might suspect otherwise.
barakandl
Jun 11, 2013, 4:34:54 PM6/11/13
to
On Jun 11, 2:35 pm, The Hammer <LHNewsgr...@frontier.com> wrote:
> in article wayout440.5ws...@rrgparchive.com, wayout440 at
> wayout...@gmail.com wrote on 6/11/13 7:45 AM:
amps. 1458 amp will work but be quiete), 10k trim pots (sustane too),
speaker (8 ohm) is good you are left with a handful of components
that could effect volume.
R14, R15, R16, R17, R18, C6, C9, C10, C12,C13, C21 Not really anything
else it could be.
> in article wayout440.5ws...@rrgparchive.com, wayout440 at
> wayout...@gmail.com wrote on 6/11/13 7:45 AM:
>
>
>
> > What makes you certain that the board is the problem - perhaps you are
> > looking in the wrong place?
>
> I am open to suggestions.
>
> I tried a different speaker.
>
> Power to the board is good.
>
> It is being triggered by the CPU as it makes tones. If it were dead silent,
> I might suspect otherwise.
If you are confident the amps (make sure you are using the right
>
>
> > What makes you certain that the board is the problem - perhaps you are
> > looking in the wrong place?
>
> I am open to suggestions.
>
> I tried a different speaker.
>
> Power to the board is good.
>
> It is being triggered by the CPU as it makes tones. If it were dead silent,
> I might suspect otherwise.
amps. 1458 amp will work but be quiete), 10k trim pots (sustane too),
speaker (8 ohm) is good you are left with a handful of components
that could effect volume.
R14, R15, R16, R17, R18, C6, C9, C10, C12,C13, C21 Not really anything
else it could be.
The Hammer
Jun 11, 2013, 5:25:35 PM6/11/13
to
in article oOWdnfZNOosUMCvM...@giganews.com, GPE at
GPE_NoSp...@cox.net wrote on 6/10/13 9:54 PM:
>
> Don't tell me that both LM741CN are defective.
> Not buying that.
>
> ------------------------------------------------------------------------------
> -------------------------
>
> Doubtful. Check R37, R38 and C23. Broken trace?
>
> Ed
>
>
I must be looking at a different Rev of AS-2518-32. I cannot find those
components on the circuit diagram. I see R36 and two C21's. Not higher.
I have compared the output and input of U8 to U9, then U9 to U10 and do not
see a sign of a broken trace. Coupling caps seem to be OK.
I am looking at the waveform at CR1 / R7. The initial pulse is close to 11
V, but the following pulses are at about half that. I am trying to
understand why. Doing follow-up testing.
http://www.flickr.com/photos/23911413@N07/9020436772/
GPE_NoSp...@cox.net wrote on 6/10/13 9:54 PM:
>
> Don't tell me that both LM741CN are defective.
> Not buying that.
>
> ------------------------------------------------------------------------------
> -------------------------
>
> Doubtful. Check R37, R38 and C23. Broken trace?
>
> Ed
>
>
components on the circuit diagram. I see R36 and two C21's. Not higher.
I have compared the output and input of U8 to U9, then U9 to U10 and do not
see a sign of a broken trace. Coupling caps seem to be OK.
I am looking at the waveform at CR1 / R7. The initial pulse is close to 11
V, but the following pulses are at about half that. I am trying to
understand why. Doing follow-up testing.
http://www.flickr.com/photos/23911413@N07/9020436772/
GPE
Jun 11, 2013, 9:39:32 PM6/11/13
to
"barakandl" wrote in message
news:69cf657a-6c9e-4da0...@w8g2000yqf.googlegroups.com...
I didn't think about that. The trimmers -- one of them could be the
culprit.
Ed
The Hammer
Jun 11, 2013, 10:18:30 PM6/11/13
to
in article 1tednTk9jY3JTCrM...@giganews.com, GPE at
GPE_NoSp...@cox.net wrote on 6/11/13 6:39 PM:
If you are referring to RT3, it measures 10k and I have it set all the way
up. The center to the high side measures zero resistance, so it has to be
good, I think.
I am less certain about RT2. Measuring the resistance from the +12 to
ground cannot be done accurately in circuit. But it seems to operate
properly as sustain goes from zero to infinite.
Because I am lost for suggestions, I unsoldered one lead of the following
and they all tested good. I selected these components because the trace at
CR1 / R7 shows an initial peak of 11 V, but the peaks after are smaller:
R14
R13
R12
R11
R10
Caps are not shorted.
I watched the 12V supply while the tones were playing, since a decreasing
output could indicate a power problem. It was rock steady at the +12 test
point on a scope.
I still cannot get over that the board functions the same even with U9
removed. That IC is not doing its job which is to convert the current
coming from U8 into voltage. If I was getting significant voltage out of
U9, the board would be working right. But there is almost nothing to the
circuit around U9 and I know all the pins are connected as they should be.
This makes me think that U9 is bad, but I have put two new ones in there.
While RT3 measures right, I want to take it out of the circuit and put in a
10k fixed resistor and recheck the output of U9. It seems stupid to do this
since the resistance across RT3 is 10K.
I am obviously missing something and when I find it, I might be too
embarrassed to post.
GPE_NoSp...@cox.net wrote on 6/11/13 6:39 PM:
up. The center to the high side measures zero resistance, so it has to be
good, I think.
I am less certain about RT2. Measuring the resistance from the +12 to
ground cannot be done accurately in circuit. But it seems to operate
properly as sustain goes from zero to infinite.
Because I am lost for suggestions, I unsoldered one lead of the following
and they all tested good. I selected these components because the trace at
CR1 / R7 shows an initial peak of 11 V, but the peaks after are smaller:
R14
R13
R12
R11
R10
Caps are not shorted.
I watched the 12V supply while the tones were playing, since a decreasing
output could indicate a power problem. It was rock steady at the +12 test
point on a scope.
I still cannot get over that the board functions the same even with U9
removed. That IC is not doing its job which is to convert the current
coming from U8 into voltage. If I was getting significant voltage out of
U9, the board would be working right. But there is almost nothing to the
circuit around U9 and I know all the pins are connected as they should be.
This makes me think that U9 is bad, but I have put two new ones in there.
While RT3 measures right, I want to take it out of the circuit and put in a
10k fixed resistor and recheck the output of U9. It seems stupid to do this
since the resistance across RT3 is 10K.
I am obviously missing something and when I find it, I might be too
embarrassed to post.
barakandl
Jun 12, 2013, 12:49:58 AM6/12/13
to
Kerry Imming
Jun 12, 2013, 2:09:19 AM6/12/13
to
"barakandl" <bara...@gmail.com> wrote in message
news:88057d08-1b70-4448...@googlegroups.com...
>> I still cannot get over that the board functions the same even with U9
>> removed. That IC is not doing its job which is to convert the current
>> coming from U8 into voltage. If I was getting significant voltage out of
>> U9, the board would be working right. But there is almost nothing to
>> the
>> circuit around U9 and I know all the pins are connected as they should
>> be.
>> This makes me think that U9 is bad, but I have put two new ones in there.
Since you've exhausted all other possible problems and I assume you've check
>> removed. That IC is not doing its job which is to convert the current
>> coming from U8 into voltage. If I was getting significant voltage out of
>> U9, the board would be working right. But there is almost nothing to
>> the
>> circuit around U9 and I know all the pins are connected as they should
>> be.
>> This makes me think that U9 is bad, but I have put two new ones in there.
resistance equal to zero for all schematic connections from the 741 op-amp
(U9), both bottom and top (if they exist) traces ....
Where did you get your new 741s? Are all the new ones you installed from
the same vendor? A reliable (non ebay) vendor?
- Kerry
The Hammer
Jun 12, 2013, 12:53:11 PM6/12/13
to
in article 88057d08-1b70-4448...@googlegroups.com, barakandl
at bara...@gmail.com wrote on 6/11/13 9:49 PM:
If I said it is input identical to output, I was misleading. The voltage
is so low on input and output of U9 as to be almost unreadable. Removing U9
from the circuit has no effect on the volume / output of the board. Given
R17 and the 10K pot RT3, one would expect the voltage to drop in half.
If I understand this circuit correctly, U9 converts the current of U8 into
voltage usable by U10. So I would expect the signal read by my scope to be
very low at the input to U9 but significantly higher on the output - it is
(essentially) unchanged.
at bara...@gmail.com wrote on 6/11/13 9:49 PM:
> If U9 input is identical to its output(p2 in p8 out) then R17 could be assumed
> to be shorted. I would see this to be the only way for U9 to have no effect
> on the amplification circuit.
I was hoping you are right, but R17 measures at 10K.
> to be shorted. I would see this to be the only way for U9 to have no effect
> on the amplification circuit.
If I said it is input identical to output, I was misleading. The voltage
is so low on input and output of U9 as to be almost unreadable. Removing U9
from the circuit has no effect on the volume / output of the board. Given
R17 and the 10K pot RT3, one would expect the voltage to drop in half.
If I understand this circuit correctly, U9 converts the current of U8 into
voltage usable by U10. So I would expect the signal read by my scope to be
very low at the input to U9 but significantly higher on the output - it is
(essentially) unchanged.
The Hammer
Jun 12, 2013, 1:01:57 PM6/12/13
to
in article kp931c$53d$1...@dont-email.me, Kerry Imming at kcim...@pobox.com
wrote on 6/11/13 11:09 PM:
I keep waiting for that 'aw crap how could I have missed that' moment so I
went back and checked continuity from each leg of that IC to another
component leg. They are all good. And I visually confirmed that the legs
that are not to be connected are not.
The source of those two chips are THE absolute most reliable source of ICs.
But stuff happens. Unless I come up with some other options, I am going to
order some more of those ICs, just to confirm.
wrote on 6/11/13 11:09 PM:
went back and checked continuity from each leg of that IC to another
component leg. They are all good. And I visually confirmed that the legs
that are not to be connected are not.
The source of those two chips are THE absolute most reliable source of ICs.
But stuff happens. Unless I come up with some other options, I am going to
order some more of those ICs, just to confirm.
GPE
Jun 12, 2013, 9:30:10 PM6/12/13
to
"Kerry Imming" wrote in message news:kp931c$53d$1...@dont-email.me...
Where did you get your new 741s? Are all the new ones you installed from
the same vendor? A reliable (non ebay) vendor?
- Kerry
I know where the 741's came from -- nice Fairchild Semiconductor's that I
bought in 2010 with 1032 date codes. I don't shop for parts on ebay and I
get a CofC for most parts (including these). Most of the older stuff I now
get from Rochester Electronics. Nice older stock but all come with CofC's
to guarantee authenticity. Unfortunately, they charge quite abit as well.
I did make the mistake of buying a bunch of National LM723CH's from a one
time poster on this newsgroup several years back. TO-5 can type regulators.
They appeared to be authentic until one was found one with only 8 pins - the
TO-5 cans should all be 10 pins. And at the same time - I got some MC6802's
and MC6821's -- all duds. Never again...
Ed
GPE
Jun 12, 2013, 9:31:17 PM6/12/13
to
"The Hammer" wrote in message
I was hoping you are right, but R17 measures at 10K.
If I said it is input identical to output, I was misleading. The voltage
is so low on input and output of U9 as to be almost unreadable. Removing U9
from the circuit has no effect on the volume / output of the board. Given
R17 and the 10K pot RT3, one would expect the voltage to drop in half.
If I understand this circuit correctly, U9 converts the current of U8 into
voltage usable by U10. So I would expect the signal read by my scope to be
very low at the input to U9 but significantly higher on the output - it is
(essentially) unchanged.
You're checking the wiper outputs of the trimmers, I assume.
Ed
The Hammer
Jun 13, 2013, 12:20:30 AM6/13/13
to
in article r5idnRsa1up5vSTM...@giganews.com, GPE at
GPE_NoSp...@cox.net wrote on 6/12/13 6:31 PM:
I have checked that both pots read 10K. When I have RT3 turned all the way
up, the resistance from the wiper to the top is zero.
When I turn RT2 all the way up, I get something like 2.3 volts applied to
pin 3 U8 which is what we would expect with that resistor network. There is
a sustained tone at that point, that is equal in loudness as those during
soundboard test, but insufficiently loud.
In studying the 741, it was never designed to be run off a single ended
supply but should have a +12 & -12 supply. Running it with a single ended
supply puts it under stress that it was not designed for and violates the
operations specs (as I understand them). Bally should have at least
created a resistor network so that pin 2 is biased at midpoint (6 V).
I am trying to figure out a mod that would either supply -12 to this board
(not easy), bias pin 2 properly, or sub a op-amp designed to run off of a
single-ended supply. All of this is likely a thankless task, unless others
start frying up their 741 when installing a non-1979 chip.
Considering that I can remove U9 from the circuit with absolutely no effect,
I cannot figure out how it cannot be the chip, unless I missed something
(senility is creeping in). Given that I just checked for the 4th time
continuity from the IC pins to another component lead, I cannot figure out
what that might be.
But if I find I messed up, I will post it, then never again be this
username.
GPE_NoSp...@cox.net wrote on 6/12/13 6:31 PM:
up, the resistance from the wiper to the top is zero.
When I turn RT2 all the way up, I get something like 2.3 volts applied to
pin 3 U8 which is what we would expect with that resistor network. There is
a sustained tone at that point, that is equal in loudness as those during
soundboard test, but insufficiently loud.
In studying the 741, it was never designed to be run off a single ended
supply but should have a +12 & -12 supply. Running it with a single ended
supply puts it under stress that it was not designed for and violates the
operations specs (as I understand them). Bally should have at least
created a resistor network so that pin 2 is biased at midpoint (6 V).
I am trying to figure out a mod that would either supply -12 to this board
(not easy), bias pin 2 properly, or sub a op-amp designed to run off of a
single-ended supply. All of this is likely a thankless task, unless others
start frying up their 741 when installing a non-1979 chip.
Considering that I can remove U9 from the circuit with absolutely no effect,
I cannot figure out how it cannot be the chip, unless I missed something
(senility is creeping in). Given that I just checked for the 4th time
continuity from the IC pins to another component lead, I cannot figure out
what that might be.
But if I find I messed up, I will post it, then never again be this
username.
The Hammer
Jun 13, 2013, 12:25:21 AM6/13/13
to
in article 0KGdneS-wqM8vSTM...@giganews.com, GPE at
GPE_NoSp...@cox.net wrote on 6/12/13 6:30 PM:
Ed, you have the most reliable components, at the best price, the highest
in-stock rate, with the fastest shipping and the best technical support.
Your ability to get those hard-to-find components is unsurpassed.
GPE_NoSp...@cox.net wrote on 6/12/13 6:30 PM:
in-stock rate, with the fastest shipping and the best technical support.
Your ability to get those hard-to-find components is unsurpassed.
The Hammer
Jun 13, 2013, 7:09:09 PM6/13/13
to
in article CDDE969E.4266A%LHNew...@frontier.com, The Hammer at
LHNew...@frontier.com wrote on 6/12/13 9:20 PM:
2 x 1k resistors. One from gnd to pin 2 of U9. The other from pin 2 of U9
to +12 VDC. This will bias pin 2 to 6 VDC.
C8 will be the blocking cap.
1 uF electrolytic Cap inserted between U9 pin 6 and RT3, to keep the voltage
from flowing through the pot. + side towards U9. A 0.05 disk might work
just fine.
Two caps, 3.3 uF and 0.1 uF in parallel from U9 pin 2 to gnd, to remove
residual noise from the 12 V being introduced via the bias. The 3.3 could
be tantalum or electrolytic with + on the pin 2 side. The 0.1 can be a
ceramic disk.
I am not suggesting anyone do this mod. This would just change the existing
circuit so that the 741 would be running as per specs.
LHNew...@frontier.com wrote on 6/12/13 9:20 PM:
>
> I am trying to figure out a mod that would either supply -12 to this board
> (not easy), bias pin 2 properly, or sub a op-amp designed to run off of a
> single-ended supply. All of this is likely a thankless task, unless others
> start frying up their 741 when installing a non-1979 chip.
>
In the useless trivia dept, here is what I think the mod should be:
> I am trying to figure out a mod that would either supply -12 to this board
> (not easy), bias pin 2 properly, or sub a op-amp designed to run off of a
> single-ended supply. All of this is likely a thankless task, unless others
> start frying up their 741 when installing a non-1979 chip.
>
2 x 1k resistors. One from gnd to pin 2 of U9. The other from pin 2 of U9
to +12 VDC. This will bias pin 2 to 6 VDC.
C8 will be the blocking cap.
1 uF electrolytic Cap inserted between U9 pin 6 and RT3, to keep the voltage
from flowing through the pot. + side towards U9. A 0.05 disk might work
just fine.
Two caps, 3.3 uF and 0.1 uF in parallel from U9 pin 2 to gnd, to remove
residual noise from the 12 V being introduced via the bias. The 3.3 could
be tantalum or electrolytic with + on the pin 2 side. The 0.1 can be a
ceramic disk.
I am not suggesting anyone do this mod. This would just change the existing
circuit so that the 741 would be running as per specs.
Barry
Jun 14, 2013, 12:20:37 PM6/14/13
to
Perhaps a review and re-test using the information from the following
web site will help in the discovery of the root cause of your low level
sound problem.
http://www.pinball4you.ch/okaegi/rep_soundold.html
--
Barry
barakandl
Jun 16, 2013, 10:04:28 AM6/16/13
to
"If sound is heard, but you can't turn the volume up
replace u9 (LM741)
Someone called "drugi" in a german pinballforum found an interesting detail about the 741 and the AS-2518-32 board:
If you replace the lm741 with a 741 from a different manufacturer (for example st -> ua741), then you have to modify the as-2518-32 board first."
John Robertson
Jun 16, 2013, 10:43:46 AM6/16/13
to
another manufacturer doesn't work quite the same as the original. I do
recall service bulletins from various manufacturers saying that when
repairing certain circuit boards that you HAD to use parts from TI or
National (or whoever) as the design parameters of the circuit took that
makers part only for ti to run as expected.
This is usually in the analogue side of things - LM3900, LM741, etc.
however even the odd TTL part had to be from a specific manufacturer or
the circuit wouldn't work. Galaga for example required a particular TTL
version on the clock circuit or the game would give intermittent
problems (I know - it's not a pinball).
John :-#)#
--
(Please post followups or tech enquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."
barakandl
Jun 18, 2013, 9:59:35 PM6/18/13
to
I am repairing for someone a -32 board that has a 3rd trim pot (adjusting it makes the pitch change). Came in with a completely blown out 12v regulation section. Replaced many parts including a shorted 555 timer sinking a ton of current, Q1, C17, CR4, 4.7k 1w resistor, 75 ohm 5w resistor and i think more to get a good +12v line.
Once I had a good +12v i found at least the LM741 to be bad, but i replaced both amps at once while the iron was hot. After replacing both amps i get correct sound but it is quiet compared to other boards. The trim pot (which i replaced) adjusts the volume but not to a normal level. I do not get the excessive speaker crackles when a normal over adjusted volume pot gives.
I know the amps are good as i have swapped them into other known good boards. I am going to dig into it more.
barakandl
Jun 18, 2013, 10:32:51 PM6/18/13
to
When checking the LM741 U9, typically when touching a probe to pin 2 you get a speaker pop/noise on when working properly. Just noticed on this board, get no pop and the volume slowly and slightly rises when the probe lead touches it.
kbliznick
Jun 18, 2013, 11:18:23 PM6/18/13
to
You might be on to something with the LM741's.
I am currently trying to repair two -32 boards. one of them has severely distorted sound (the one with 3 trim pots), the other one was completely dead (no hum from the amps)
I replaced both amps to start on the dead one with no luck, Replaced them both on the distorted one and I got no sounds at all.
Put the old parts back in one at a time to discover that the new LM741 is not working with the board, try the one from the other board as well. Both new LM741's are not working.
Put the old amps back into both boards. Find an open R22 on the dead board and now it works but I have no sustain to the notes.
Both boards already have all new electrolytic caps. One has the 729-18 rom, the other one is different but don't recall right now which one.
I am currently trying to repair two -32 boards. one of them has severely distorted sound (the one with 3 trim pots), the other one was completely dead (no hum from the amps)
I replaced both amps to start on the dead one with no luck, Replaced them both on the distorted one and I got no sounds at all.
Put the old parts back in one at a time to discover that the new LM741 is not working with the board, try the one from the other board as well. Both new LM741's are not working.
Put the old amps back into both boards. Find an open R22 on the dead board and now it works but I have no sustain to the notes.
Both boards already have all new electrolytic caps. One has the 729-18 rom, the other one is different but don't recall right now which one.
barakandl
Jun 18, 2013, 11:31:48 PM6/18/13
to
Tomorrow i am going to go pin by pin on both amps and the weird 4048 compared to a known good board.
barakandl
Jun 18, 2013, 11:32:34 PM6/18/13
to
barakandl
Jun 19, 2013, 3:56:22 PM6/19/13
to
On Jun 18, 11:32 pm, barakandl <baraka...@gmail.com> wrote:
> On Tuesday, June 18, 2013 11:31:48 PM UTC-4, barakandl wrote:
> > On Tuesday, June 18, 2013 11:18:23 PM UTC-4, kbliznick wrote:
>
> > > You might be on to something with the LM741's.
>
> > > I am currently trying to repair two -32 boards. one of them has severely distortedsound(the one with 3 trim pots), the other one was completely dead (no hum from the amps)
> On Tuesday, June 18, 2013 11:31:48 PM UTC-4, barakandl wrote:
> > On Tuesday, June 18, 2013 11:18:23 PM UTC-4, kbliznick wrote:
>
> > > You might be on to something with the LM741's.
>
>
> > > I replaced both amps to start on the dead one with no luck, Replaced them both on the distorted one and I got no sounds at all.
>
> > > Put the old parts back in one at a time to discover that the new LM741 is not working with the board, try the one from the other board as well. Both new LM741's are not working.
>
> > > Put the old amps back into both boards. Find an open R22 on the dead board and now it works but I have no sustain to the notes.
>
> > > Both boards already have all new electrolytic caps. One has the 729-18 rom, the other one is different but don't recall right now which one.
>
> > I have five of these similarsoundboards in right now. I repaired four of them, and have swapped components between them. I am confident my LM741s are good and work with this board as i have used a few and swapped around. Something is going on in the amplification section i have not found yet.
> > > I replaced both amps to start on the dead one with no luck, Replaced them both on the distorted one and I got no sounds at all.
>
> > > Put the old parts back in one at a time to discover that the new LM741 is not working with the board, try the one from the other board as well. Both new LM741's are not working.
>
> > > Put the old amps back into both boards. Find an open R22 on the dead board and now it works but I have no sustain to the notes.
>
> > > Both boards already have all new electrolytic caps. One has the 729-18 rom, the other one is different but don't recall right now which one.
>
>
> > Tomorrow i am going to go pin by pin on both amps and the weird 4048 compared to a known good board.
>
> *****4049 typo- Hide quoted text -
> > Tomorrow i am going to go pin by pin on both amps and the weird 4048 compared to a known good board.
>
>
> - Show quoted text -
Being bored at work, i just checked schematics for -50 and the -32
boards and there is some differences around the 741 amp. The later
sound boards have on the 741 pin 3 two 10k resistors dividing 12v and
a 1uf electrolytic cap to ground. The earlier -32 sound boards have
just the amp pin 3 connected to ground.
Could this be why Hammer and I have trouble? New lm741 amps don't
like pin3 tied to ground?
barakandl
Jun 19, 2013, 3:58:56 PM6/19/13
to
On Jun 19, 3:56 pm, barakandl <baraka...@gmail.com> wrote:
> On Jun 18, 11:32 pm, barakandl <baraka...@gmail.com> wrote:
>
>
>
>
>
> > On Tuesday, June 18, 2013 11:31:48 PM UTC-4, barakandl wrote:
> > > On Tuesday, June 18, 2013 11:18:23 PM UTC-4, kbliznick wrote:
>
> > > > You might be on to something with the LM741's.
>
> > > > I am currently trying to repair two -32 boards. one of them has severely distortedsound(the one with 3 trim pots), the other one was completely dead (no hum from the amps)
>
> > > > I replaced both amps to start on the dead one with no luck, Replaced them both on the distorted one and I got no sounds at all.
>
> > > > Put the old parts back in one at a time to discover that the new LM741 is not working with the board, try the one from the other board as well. Both new LM741's are not working.
>
> > > > Put the old amps back into both boards. Find an open R22 on the dead board and now it works but I have no sustain to the notes.
>
> > > > Both boards already have all new electrolytic caps. One has the 729-18 rom, the other one is different but don't recall right now which one.
>
> > > I have five of these similarsoundboards in right now. I repaired four of them, and have swapped components between them. I am confident my LM741s are good and work with this board as i have used a few and swapped around. Something is going on in the amplification section i have not found yet.
>
> > > Tomorrow i am going to go pin by pin on both amps and the weird 4048 compared to a known good board.
>
> > *****4049 typo- Hide quoted text -
>
> > - Show quoted text -
>
> Being bored at work, i just checked schematics for -50 and the -32
> boards and there is some differences around the 741 amp. The latersoundboards have on the 741 pin 3 two 10k resistors dividing 12v and
> On Jun 18, 11:32 pm, barakandl <baraka...@gmail.com> wrote:
>
>
>
>
>
> > On Tuesday, June 18, 2013 11:31:48 PM UTC-4, barakandl wrote:
> > > On Tuesday, June 18, 2013 11:18:23 PM UTC-4, kbliznick wrote:
>
> > > > You might be on to something with the LM741's.
>
> > > > I am currently trying to repair two -32 boards. one of them has severely distortedsound(the one with 3 trim pots), the other one was completely dead (no hum from the amps)
>
> > > > I replaced both amps to start on the dead one with no luck, Replaced them both on the distorted one and I got no sounds at all.
>
> > > > Put the old parts back in one at a time to discover that the new LM741 is not working with the board, try the one from the other board as well. Both new LM741's are not working.
>
> > > > Put the old amps back into both boards. Find an open R22 on the dead board and now it works but I have no sustain to the notes.
>
> > > > Both boards already have all new electrolytic caps. One has the 729-18 rom, the other one is different but don't recall right now which one.
>
> > > I have five of these similarsoundboards in right now. I repaired four of them, and have swapped components between them. I am confident my LM741s are good and work with this board as i have used a few and swapped around. Something is going on in the amplification section i have not found yet.
>
> > > Tomorrow i am going to go pin by pin on both amps and the weird 4048 compared to a known good board.
>
> > *****4049 typo- Hide quoted text -
>
> > - Show quoted text -
>
> Being bored at work, i just checked schematics for -50 and the -32
> a 1uf electrolytic cap to ground. The earlier -32soundboards have
> just the amp pin 3 connected to ground.
>
> Could this be why Hammer and I have trouble? New lm741 amps don't
> like pin3 tied to ground?- Hide quoted text -
>
> Could this be why Hammer and I have trouble? New lm741 amps don't
>
> - Show quoted text -
Here is the schematic around the amp.
> - Show quoted text -
-50 with the extra components
http://imageshack.us/a/img837/7264/xk1.png
-32 missing the extra components
http://imageshack.us/a/img268/1474/1jnv.png
barakandl
Jun 19, 2013, 8:45:34 PM6/19/13
to
It is the brand of LM741 you use. Out of three varieties i checked, only one style would work properly on the -32 board. The -50 board works with any lm741 amp i have tried.
So if you need to replace the 741 on the -32 sound board you either mod the board adding the extra two resistors and electrolytic cap seen the in -50 schematic above or use the brand of amp shown in my picture below that is on the left. The middle and right brand does not work in a -32 board (but works in a -50).
http://img593.imageshack.us/img593/8500/xyf4.jpg
John Robertson
Jun 19, 2013, 9:44:50 PM6/19/13
to
didn't. Not surprising as NS was (I believe) the second source for
Fairchild's original UA741.
GPE
Jun 19, 2013, 9:51:16 PM6/19/13
to
"barakandl" wrote in message
news:6dd0c189-a000-4acc...@googlegroups.com...
Figured it out.
It is the brand of LM741 you use. Out of three varieties i checked, only
one style would work properly on the -32 board. The -50 board works with
any lm741 amp i have tried.
So if you need to replace the 741 on the -32 sound board you either mod the
board adding the extra two resistors and electrolytic cap seen the in -50
schematic above or use the brand of amp shown in my picture below that is on
the left. The middle and right brand does not work in a -32 board (but
works in a -50).
http://img593.imageshack.us/img593/8500/xyf4.jpg
----------------------------------------------------
It is the brand of LM741 you use. Out of three varieties i checked, only
one style would work properly on the -32 board. The -50 board works with
any lm741 amp i have tried.
So if you need to replace the 741 on the -32 sound board you either mod the
board adding the extra two resistors and electrolytic cap seen the in -50
schematic above or use the brand of amp shown in my picture below that is on
the left. The middle and right brand does not work in a -32 board (but
works in a -50).
http://img593.imageshack.us/img593/8500/xyf4.jpg
Been watching this...
So, the National Semiconductor part from 1978 works but the others do not -
including the much newer National Semi part pictured on the right. And now
that National Semiconductor no longer exists -- Hopefully TI made parts will
work (TI bought National Semi). Otherwise, I imagine a lot more people
will need to add the voltage divider inputs.
BTW - was it you that stated the values of the divider resistors were wrong
on the schematics? That it was a 15K & 10K instead of a 10K and 10K? Or
was that a different thread?
Ed
The Hammer
Jun 19, 2013, 11:15:45 PM6/19/13
to
in article 0cd1856a-a860-42ca...@googlegroups.com, kbliznick
at kbli...@aol.com wrote on 6/18/13 8:18 PM:
I have been away from this thread as I was waiting for the part. I had no
idea this discussion was going on.
I got the part today from another source, but have not done anything with it
yet.
I would have suspected that with R22 open, that would have messed up your 12
volt power supply?
at kbli...@aol.com wrote on 6/18/13 8:18 PM:
idea this discussion was going on.
I got the part today from another source, but have not done anything with it
yet.
I would have suspected that with R22 open, that would have messed up your 12
volt power supply?
The Hammer
Jun 19, 2013, 11:30:25 PM6/19/13
to
in article 22f437c6-017e-491b...@i1g2000yqo.googlegroups.com,
barakandl at bara...@gmail.com wrote on 6/19/13 12:56 PM:
In one of my earlier posts, a friend of mine pointed out to me that the 741
is designed to be run with a +/- power supply. By having pin 2 and pin 3 at
the same voltage, the 741 is running outside of the operational specs (not
certain how pin 2 ends up with +2VDC, but it is internally derived rather
than externally applied).
It could be that the modification made in the -50 board, as posted by
barakandl was Bally's attempt to run the 741 within specs, without creating
a -12V supply. That circuit puts pin 3 at +6 V, which is mid voltage,
creating the effect of a +/- supply.
That was in effect, what I was trying to do below. They just did it on pin
3 rather than pin 2. The advantage of their design vs. what I suggested is
that no blocking cap is needed at RT3 to keep the +6 applied to pin 2 from
flowing through R17 / RT3.
Here was the suggested mod below:
barakandl at bara...@gmail.com wrote on 6/19/13 12:56 PM:
is designed to be run with a +/- power supply. By having pin 2 and pin 3 at
the same voltage, the 741 is running outside of the operational specs (not
certain how pin 2 ends up with +2VDC, but it is internally derived rather
than externally applied).
It could be that the modification made in the -50 board, as posted by
barakandl was Bally's attempt to run the 741 within specs, without creating
a -12V supply. That circuit puts pin 3 at +6 V, which is mid voltage,
creating the effect of a +/- supply.
That was in effect, what I was trying to do below. They just did it on pin
3 rather than pin 2. The advantage of their design vs. what I suggested is
that no blocking cap is needed at RT3 to keep the +6 applied to pin 2 from
flowing through R17 / RT3.
Here was the suggested mod below:
barakandl
Jun 19, 2013, 11:36:53 PM6/19/13
to
Different voltage divide that is a misprint on the component list for the -32 board. The -32 component list says R28 is 4.7k resistor which is incorrect. R28 is actually a 15k resistor.
barakandl
Jun 19, 2013, 11:46:07 PM6/19/13
to
The 12v supply had major problems on this board. My guess is the 555 timer probably went when the tip29 shorted. Once the 555 timer shorted it started sucking down a ton of current burning the power resistors and taking out the zener diode.
Before i replaced the 555 timer, the 12v line was 5v and the power resistors started to burn again. I guessed 380n amplifier first and was incorrect. Next I cut the 12v line trace to try and find where the short was. This led to the timer.
The Hammer
Jun 19, 2013, 11:51:33 PM6/19/13
to
in article bOadnd-WG4mJ_V_M...@giganews.com, GPE at
GPE_NoSp...@cox.net wrote on 6/19/13 6:51 PM:
>
> Been watching this...
> So, the National Semiconductor part from 1978 works but the others do not -
> including the much newer National Semi part pictured on the right. And now
> that National Semiconductor no longer exists -- Hopefully TI made parts will
> work (TI bought National Semi). Otherwise, I imagine a lot more people
> will need to add the voltage divider inputs.
> BTW - was it you that stated the values of the divider resistors were wrong
> on the schematics? That it was a 15K & 10K instead of a 10K and 10K? Or
> was that a different thread?
>
> Ed
>
>
>
I am guessing that both should be 10K as the point is to drive the 741 with
a simulated +/- power supply. Ideally, Bally should have provided a -12
supply along with the +12. But the way around that operational spec is to
create a 0/+6/+12 supply using a divider network. By using a 10K / 10K
voltage divider, pin 3 would have +6 applied.
The 1 uF cap is a good idea to filter noise. A 3.3 uF in parallel with 0.1
uF would be better, but heck, this is a noisy circuit to begin with. No
issue with adding a little bit more.
http://www.ti.com/lit/ds/symlink/lm741.pdf
What I am not clear about, is how applying +6 to pin 3 allows it to run
within specs. Since -12 should be applied to pin 4, to simulate a +/-
supply, I would have run pin 4 at ground and pin 2 at +6. I guess having
the audio input at pin 2, and the +6 V at pin 3 accomplishing the same goal?
For those wanting to dig into the detail, check out Chapter 4:
http://focus.ti.com/lit/an/slod006b/slod006b.pdf
GPE_NoSp...@cox.net wrote on 6/19/13 6:51 PM:
>
> Been watching this...
> So, the National Semiconductor part from 1978 works but the others do not -
> including the much newer National Semi part pictured on the right. And now
> that National Semiconductor no longer exists -- Hopefully TI made parts will
> work (TI bought National Semi). Otherwise, I imagine a lot more people
> will need to add the voltage divider inputs.
> BTW - was it you that stated the values of the divider resistors were wrong
> on the schematics? That it was a 15K & 10K instead of a 10K and 10K? Or
> was that a different thread?
>
> Ed
>
>
>
a simulated +/- power supply. Ideally, Bally should have provided a -12
supply along with the +12. But the way around that operational spec is to
create a 0/+6/+12 supply using a divider network. By using a 10K / 10K
voltage divider, pin 3 would have +6 applied.
The 1 uF cap is a good idea to filter noise. A 3.3 uF in parallel with 0.1
uF would be better, but heck, this is a noisy circuit to begin with. No
issue with adding a little bit more.
http://www.ti.com/lit/ds/symlink/lm741.pdf
What I am not clear about, is how applying +6 to pin 3 allows it to run
within specs. Since -12 should be applied to pin 4, to simulate a +/-
supply, I would have run pin 4 at ground and pin 2 at +6. I guess having
the audio input at pin 2, and the +6 V at pin 3 accomplishing the same goal?
For those wanting to dig into the detail, check out Chapter 4:
http://focus.ti.com/lit/an/slod006b/slod006b.pdf
The Hammer
Jun 20, 2013, 12:10:57 AM6/20/13
to
in article 0bf1a66e-c97c-4348...@googlegroups.com, barakandl
at bara...@gmail.com wrote on 6/19/13 8:36 PM:
>> http://img593.imageshack.us/img593/8500/xyf4.jpg
>>
>>
Oh, and crap, mine looks like the one on the right.
Crap.
Dang.
Crap.
Kerry Imming
Jun 20, 2013, 7:45:03 AM6/20/13
to
On Jun 19, 10:51 pm, The Hammer <LHNewsgr...@frontier.com> wrote:
>
> What I am not clear about, is how applying +6 to pin 3 allows it to run
> within specs. Since -12 should be applied to pin 4, to simulate a +/-
> supply, I would have run pin 4 at ground and pin 2 at +6. I guess having
> the audio input at pin 2, and the +6 V at pin 3 accomplishing the same goal?
>
We mislead people by talking about "ground". In this case it's really
>
> What I am not clear about, is how applying +6 to pin 3 allows it to run
> within specs. Since -12 should be applied to pin 4, to simulate a +/-
> supply, I would have run pin 4 at ground and pin 2 at +6. I guess having
> the audio input at pin 2, and the +6 V at pin 3 accomplishing the same goal?
>
just
a reference voltage. We usually use 0 volts as reference and hence
ground
and reference are the usually the same.
The 741 doesn't know what ground is, it only knows the relative
voltage on
its pins. Usually a split supply (+/- 12V) is convenient because the
AC
input signal is usually centered around zero volts. The real
datasheet
limit is that you can't exceed the supply voltage on any input. If
you are
using 0 and +12 as the supply voltage, the input must limit its swing
between 0 and +12V. Centering the AC voltage at +6V gives you the
maximum
AC range in that case.
I'm sure others can explain this better than me, feel free to chime
in.
- Kerry
Gott Lieb?
Jun 20, 2013, 7:58:12 AM6/20/13
to
Jim
The Hammer
Jun 20, 2013, 1:03:52 PM6/20/13
to
in article 36432a00-1483-4fc7...@10g2000yqy.googlegroups.com,
Kerry Imming at kerry....@gmail.com wrote on 6/20/13 4:45 AM:
Thanks Kerry for the explanation. What I was referring to was bringing pin
3 up to +6 vs. doing the same thing to pin 2 (which was my earlier post on a
potential circuit mod).
After doing some additional research, I realized that a designer would
normally apply -DC to pin 4 and +DC to pin 7 and ground pin 3 with inverting
input to pin 2. By applying the voltage divider to pin 3 (rather than as I
suggested to pin 2), they are doing what you described (and I was trying to
do), creating the effect of a +/- DC supplied to pins 7 & 4. So my
suggested mod was fine, except that it should have been applied to pin 3 (or
the input to the IC that is not connected to the audio).
I guess if I want to get this board going with the ICs I have, I am going to
have to come up with a way to insert those 10K resistors. I will try it
without that cap first, just to see if it works and how noisy it is.
Kerry Imming at kerry....@gmail.com wrote on 6/20/13 4:45 AM:
3 up to +6 vs. doing the same thing to pin 2 (which was my earlier post on a
potential circuit mod).
After doing some additional research, I realized that a designer would
normally apply -DC to pin 4 and +DC to pin 7 and ground pin 3 with inverting
input to pin 2. By applying the voltage divider to pin 3 (rather than as I
suggested to pin 2), they are doing what you described (and I was trying to
do), creating the effect of a +/- DC supplied to pins 7 & 4. So my
suggested mod was fine, except that it should have been applied to pin 3 (or
the input to the IC that is not connected to the audio).
I guess if I want to get this board going with the ICs I have, I am going to
have to come up with a way to insert those 10K resistors. I will try it
without that cap first, just to see if it works and how noisy it is.
The Hammer
Jun 20, 2013, 5:57:25 PM6/20/13
to
in article CDE88408.43ABB%LHNew...@frontier.com, The Hammer at
LHNew...@frontier.com wrote on 6/20/13 10:03 AM:
I put in the 2 x 10K resistors with one of the original chips and it is much
louder now.
I did not put in the cap as I just wanted to prove feasibility.
Since this is my first exposure to this generation of Bally -32 sound
boards, I am not certain what proper operation is. When I turn the volume
all the way up, instead of getting louder, it gets distorted. I guess that
is a sign of overloading U10.
I did the mod (borderline hack) on the foil side. It is a challenge because
pins 4 & 3 are connected together, and the ground comes off of 4. I tried
using a knife to cut the trace but ended up using a dremel cutter. I then
soldered 1/4 W resistors directly to the pin from ground and +12.
http://img32.imageshack.us/img32/1558/xr01.jpg
LHNew...@frontier.com wrote on 6/20/13 10:03 AM:
I put in the 2 x 10K resistors with one of the original chips and it is much
louder now.
I did not put in the cap as I just wanted to prove feasibility.
Since this is my first exposure to this generation of Bally -32 sound
boards, I am not certain what proper operation is. When I turn the volume
all the way up, instead of getting louder, it gets distorted. I guess that
is a sign of overloading U10.
I did the mod (borderline hack) on the foil side. It is a challenge because
pins 4 & 3 are connected together, and the ground comes off of 4. I tried
using a knife to cut the trace but ended up using a dremel cutter. I then
soldered 1/4 W resistors directly to the pin from ground and +12.
http://img32.imageshack.us/img32/1558/xr01.jpg
The Hammer
Jun 20, 2013, 6:10:03 PM6/20/13
to
in article CDE8C8D5.43D79%LHNew...@frontier.com, The Hammer at
LHNew...@frontier.com wrote on 6/20/13 2:57 PM:
barakandl
Jun 20, 2013, 10:22:25 PM6/20/13
to
The Hammer
Jun 21, 2013, 12:18:09 AM6/21/13
to
in article 3763fcbf-63b3-419d...@googlegroups.com, barakandl
at bara...@gmail.com wrote on 6/20/13 7:22 PM:
>
> Normal operation max volume will damn near blow out your speaker and tons of
> static. Typically i adjust this pot about 30%.
That's just it. It does not sound loud in the speaker. It just distorts,
like I am overloading the input of the amp. When I back it off, to about
50%, the distortion goes away.
It did not sound like the speaker is overloaded.
I am good with its current volume, which is much louder than before the mod,
although if all my pins get played at the same time, this will get drowned
out. I need to pull out another speaker and try it.
I replaced U10, so, in theory, that is not the problem. Will check the
board again...
at bara...@gmail.com wrote on 6/20/13 7:22 PM:
>
> Normal operation max volume will damn near blow out your speaker and tons of
> static. Typically i adjust this pot about 30%.
like I am overloading the input of the amp. When I back it off, to about
50%, the distortion goes away.
It did not sound like the speaker is overloaded.
I am good with its current volume, which is much louder than before the mod,
although if all my pins get played at the same time, this will get drowned
out. I need to pull out another speaker and try it.
I replaced U10, so, in theory, that is not the problem. Will check the
board again...
The Hammer
Jun 23, 2013, 7:39:47 PM6/23/13
to
in article CDE92211.44309%LHNew...@frontier.com, The Hammer at
LHNew...@frontier.com wrote on 6/20/13 9:18 PM:
I put in a 1 uF cap on pin 3 of the 741, negative to ground, as shown in the
-50 schematic. It made a huge difference - now 10x louder.
All fixed now.
Thanks everyone for your help.
So to summarize:
If replacing the 741 on a -32 sound board, if the replacement does not work,
you will need to make the mod on pin 3 of U9 as shown on the -50 schematic.
http://imageshack.us/a/img837/7264/xk1.png
LHNew...@frontier.com wrote on 6/20/13 9:18 PM:
-50 schematic. It made a huge difference - now 10x louder.
All fixed now.
Thanks everyone for your help.
So to summarize:
If replacing the 741 on a -32 sound board, if the replacement does not work,
you will need to make the mod on pin 3 of U9 as shown on the -50 schematic.
http://imageshack.us/a/img837/7264/xk1.png
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