Grundig AM/FM portable "Transistor 305" troubleshooting

[klem kedidelhopper]

I would like to ask for help once again with the repair of my own
personal old radio. I started this project almost a year ago, and it's
been on the back burner since then. But I had a little free time and
so I put it back on the bench. I would really like to see this radio
working again.

This is a Grundig "transistor 305", circa 1970 I think. The radio is
intermittent. I have been working on this set on and off for almost
the past year. I recently took some voltage measurements and there are
some serious differences in base and emitter voltages in the last IF
stage and the detector stage when this radio fails. I have tried many
things, heat and cold, including substituting all the transistors in
the RF and IF sections one at a time and have studied the schematic
until I felt a migraine coming on. l think that by now I could almost
draw it from memory, and I'm still coming up empty.

I considered trying to inject a signal and/or signal tracing, however
with the circuit voltages so far out of whack when it fails I think
that approach would be futile. The base and emitter voltages in these
three stages increase substantially when the radio quits. Some
voltages are jumping from for example 1.2V up to 4.0 V. With
conditions like this you would think that the cause would be obvious,
and perhaps I've been staring at this this too long and it is. However
the remedy has stubbornly eluded me thus far. The intermittent nature
of the problem is what makes it so difficult.

This is typical of what is going on: If the radio has been off for a
long period of time it will typically work for several hours and then
quit. In the beginning of this Quitting sequence, just after it first
quits it will try to come back on intermittently for a short period of
time, crackling etc, (as though something was intermittently breaking
down). Eventually it will just remain silent. There was an
electrolytic in the audio driver section, C57 a 100uf/3.0 volt with
slightly high ESR. Replacing it improved the low frequency audio
response, however the AF amplifier is not the problem though. You can
still get a good audio signal from the volume control out when it
fails. So the AF section seems to be unaffected. The voltages to that
part of the circuit substantiate that as well. And the RF and
oscillator circuit voltages during dead time seem to be fine as well.
The problem when it occurs affects both AM and FM.

The strange thing is that when powering this radio up again after a
shut down, the time it remains on before it quits once again is
directly proportional to the time that it has been off. For instance
if you leave it off overnight it might remain on for a half hour or so
the next morning before it quits again. Recently after trying it again
after months of it sitting idle it played for about 3 hours before it
quit. Then five minutes later when trying it again it quit almost
immediately. The few other electrolytics in the affected areas check
good on ESR and bridging them during dead time yielded no improvement
either. I have the schematic and I have uploaded it to the site listed
below.

I know that there are technicians out there better at this than I am,
and I would really appreciate it if someone could please take a look
at the schematic along with the voltage readings I obtained during Go
and No Go conditions and give me your opinions. With three stages
affected I suspect that I'm looking for a common denominator but I'm
just not sure. The initial voltage readings (on turn on with the unit
working normally) will be listed in the left hand column. The voltage
readings during a failed condition are listed in the right hand
column.
The major differences are marked with an asterisk*.

I used to strap this radio to my bicycle when I was a kid and ride
around The Bronx with it. It has a great sound. I've owned it since I
was a teenager. I guess it's just a sentimental thing. Thanks for any
assistance. Lenny

http://dl.dropbox.com/u/65394789/Grundig%20large%20schematic.pdf

Voltage readings
Test point Radio working: Radio not working
------------------- --------------------
-------------------------
E. AF178 -1.10V -1.20V
B. AF178 -1.50V -1.50V
E. AF124 -1.10V -1.20V
B. AF124 -1.32V -1.44V
E. AF121 -0.85V -0.90V
B. AF121 -1.20V -1.30V
E. AF126 (1) -1.00V -3.70V *
B. AF126 (1) -1.20V -4.00V *
E. AF126 (II) -0.80V -3.70V *
B. AF126 (II) -1.10V -3.60V *
E. AC151 (I) - 0.90V -0.80V
C. AC151 (I) --3.05V -2.95V
E. AC151 (II) --0.66V -0.62V
C. AC151 (II) --3.20V -3.10V

Thanks once again for looking. Lenny

[spamtrap1888]

On Mar 4, 7:47 pm, klem kedidelhopper <captainvideo462...@gmail.com>
wrote:

> I would like to ask for help once again with the repair of my own
> personal old radio. I started this project almost a year ago, and it's
> been on the back burner since then. But I had a little free time and
> so I put it back on the bench. I would really like to see this radio
> working again.
>
> This is a Grundig "transistor 305", circa 1970 I think. The radio is
> intermittent. I have been working on this set on and off for almost
> the past year. I recently took some voltage measurements and there are
> some serious differences in base  and emitter voltages in the last  IF
> stage and the detector stage when this radio fails. I have tried many
> things, heat and cold, including substituting all the transistors in
> the RF and IF sections one at a time and have studied the schematic
> until I felt a migraine coming on. l think that by now I could almost
> draw it from memory, and I'm still coming up empty.
>

> The strange thing is that when powering this radio up again after a
> shut down, the time it remains on before it quits once again is
> directly proportional to the time that it has been off. For instance
> if you leave it off overnight it might remain on for a half hour or so
> the next morning before it quits again. Recently after trying it again
> after months of it sitting idle it played for about 3 hours before it
> quit. Then five minutes later when trying it again it quit almost
> immediately. The few other electrolytics in the affected areas check
> good on ESR and bridging them during dead time yielded no improvement
> either. I have the schematic and I have uploaded it to the site listed
> below.
>

>

> I used to strap this radio to my bicycle when I was a kid and ride
> around The Bronx with it. It has a great sound. I've owned it since I
> was a teenager. I guess it's just a sentimental thing. Thanks for any
> assistance. Lenny
>
> http://dl.dropbox.com/u/65394789/Grundig%20large%20schematic.pdf
>

"A drawing error occurred."

Try cutepdf.

[Winston]

klem kedidelhopper wrote:
> I would like to ask for help once again with the repair of my own
> personal old radio.

Hey Lenny,

It looks like a thermal intermittent.
Transistor AF126 is being told to 'cut off'
when the area around it heats sufficiently.
I suspect trim pot R22 (Just below AF126)
has a fractured solder joint which pops
open under thermal expansion.

Use your plastic spudger tool to gently
wiggle R22 and see if you can reproduce the
problem at will.

Next available moment, suggest you replace
the solder on R22 using plenty of liquid
RMA flux, then clean the area with naphtha
and an acid brush. Use lots of ventilation
and 'exam gloves' on your hands. Naphtha
is an excellent cleaner and will suck the
oil right out of your hands. DAMHIKT. :)

--Winston

[Franc Zabkar]

On Sun, 4 Mar 2012 19:47:09 -0800 (PST), klem kedidelhopper
<captainvi...@gmail.com> put finger to keyboard and composed:

>http://dl.dropbox.com/u/65394789/Grundig%20large%20schematic.pdf
>
> Voltage readings
> Test point Radio working: Radio not working
> ------------------- --------------------

> E. AF178 -1.10V -1.20V
> B. AF178 -1.50V -1.50V
> E. AF124 -1.10V -1.20V
> B. AF124 -1.32V -1.44V
> E. AF121 -0.85V -0.90V
> B. AF121 -1.20V -1.30V
> E. AF126 (1) -1.00V -3.70V *
> B. AF126 (1) -1.20V -4.00V *
> E. AF126 (II) -0.80V -3.70V *
> B. AF126 (II) -1.10V -3.60V *
> E. AC151 (I) - 0.90V -0.80V
> C. AC151 (I) --3.05V -2.95V
> E. AC151 (II) --0.66V -0.62V
> C. AC151 (II) --3.20V -3.10V

I suspect that C45 (near pin #8 of 7209-301) may be shorting.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

[klem kedidelhopper]

On Mar 5, 6:07 am, Franc Zabkar <fzab...@iinternode.on.net> wrote:
> On Sun, 4 Mar 2012 19:47:09 -0800 (PST), klem kedidelhopper

> <captainvideo462...@gmail.com> put finger to keyboard and composed:

The "whisker theory was also posed to me last time I took a crack at
this repair. I disconnected all the cans at that time but the problem
still persisted. I'm trying to understand though how C45 could affect
this? It seems like a somewhat removed part of the circuit but perhaps
I'm not seeing the whole picture. Could these two affected transistors
be turning on, and if so wouldn't the collectors be very close to the
same potential as the emitters? I never looked at that. Collector
voltages are not listed on the schematic for those stages. Still if
that isn't the case I have to try to determine how this voltage is so
drastically rising. R22 seems to set a bias point. I subjected R22 to
some stress. It's definitely not a cold solder joint on that pot.
Unless it's breaking down internally but I would have thought that my
poking and prodding would have helped that along. In fact I had hoped
that once things became "thermal" they might also become
"mechanically" intermittent as well, but that was not the case. Now
hypothetically speaking in the case of one of the 820 ohm emitter
resistors opening, would that affect both stages? So many
possibilities here. I also thought of putting the soldering iron onto
the leads of several components upon turn on to attempt to bring on
the problem ahead of the time it usually takes but I am leaving that
as a last resort. Here is another link to the schematic just in case
the first one doesn't work or fails:
http://db.tt/bbVeazAe
Lenny

[Winston]

klem kedidelhopper wrote:

> R22 seems to set a bias point. I subjected R22 to
> some stress. It's definitely not a cold solder joint on that pot.

When you re-soldered the connections to R22, did
the intermittent go away?

--Winston

[William Sommerwerck]

This is a good example of the dilemma anyone fixing an electronic product
faces -- do you want to find out exactly what's wrong, or do you just want
to get it working again?

My own bias is towards the former, but eventually one has to stop
experimenting and "fix the damn thing, already".

Given that it's battery-operated, a thermal problem seems unlikely. A bad
solder joint, or a cracked trace or solder pad seem likely. It might also be
a bad transistor.

I would unsolder all the components around the suspected-bad area, and
troubleshoot for a cracked trace/pad. If you can't find any, replace all the
unsoldered components with new ones.

[amdx]

>
> The strange thing is that when powering this radio up again after a
> shut down, the time it remains on before it quits once again is
> directly proportional to the time that it has been off. For instance
> if you leave it off overnight it might remain on for a half hour or so
> the next morning before it quits again. Recently after trying it again
> after months of it sitting idle it played for about 3 hours before it
> quit. Then five minutes later when trying it again it quit almost
> immediately. The few other electrolytics in the affected areas check
> good on ESR and bridging them during dead time yielded no improvement
> either. I have the schematic and I have uploaded it to the site listed
> below.

I have found a lot of intermittent problems with a can of freeze mist,
hair dryer and the tip of a soldering iron.
The first thing I would try is heating it with a hair dryer to see if
I could get it to go intermittent. If it does then go to your suspect
area and just barely dribble the freeze mist on, one part at a time.
It usually takes a fine touch on the freeze mist button to not
put out a big gush.
Another thing to try; touch transistors with the tip of your soldering
iron to heat it up. Sometimes you can find an intermittent transistor
this way.
Radio Shack has freeze mist.
Mikek

[spamtrap1888]

On Mar 5, 7:02 am, klem kedidelhopper <captainvideo462...@gmail.com>
wrote:

I was able to open the pdf after downloading it.

While I haven't done the math, I would suspect C44. First, it is
suspect merely by virtue of being a 40 year old electrolytic capacitor
that is connected to both failing stages. Further: if, when you turned
the radio on, C44's leakage current was initially low, but with
operation it increased substantially, then a bad C44 would affect the
bias point R22 was trying to set, as current began to flow through
R21. Moreover, a short through C44 to positive should have an effect
similar to the short through C45 to ground that Franc suspects. Thus,
I would try replacing C44.

[hrho...@att.net]

What he says is what I would do also>>>>>

[Franc Zabkar]

On Mon, 5 Mar 2012 07:02:27 -0800 (PST), klem kedidelhopper
<captainvi...@gmail.com> put finger to keyboard and composed:

>The "whisker theory was also posed to me last time I took a crack at
>this repair. I disconnected all the cans at that time but the problem
>still persisted. I'm trying to understand though how C45 could affect
>this?

Sorry, I'm not convinced that C45 is the culprit. I was confused by
the negative voltages and the upside down circuit diagram. :-(

I still think that some component is reducing the bias on the base of
AF126 (I). I was looking for a path to ground via a likely suspect,
and C45 and C46 looked like possible candidates.

As for R22, I don't understand how an open circuit could reduce the
voltage on the base of the transistor.

[Winston]

Franc Zabkar wrote:

(...)

> As for R22, I don't understand how an open circuit could reduce the
> voltage on the base of the transistor.

Emitter current through R24 is adjusted by the setting of
R22, per the note to the right of R24. As R22 is adjusted
higher in resistance, we can expect less current to flow
from the base to emitter, causing AF126 to tend towards
cutoff. (The base becomes less negative *in relation to
the emitter*).

What if we broke the connection to R22 by lifting it's rotor
or fracturing either of it's solder connections?
The base of AF126 will be biased more positive in relation
to it's emitter (towards cutoff) because R22 isn't there to
provide a parallel current path to ground.

See how the AGC rectifier (AA130) biases the base of AF126
more positive (via R21) as IF voltage increases? This
also tends to push AF126 towards cutoff. It's a negative
feedback loop that keeps IF voltage constant.


--Winston

[Dave M]

My $0.02 worth...
Since two stages are being upset, look for what's common to both circuits.
I don't know how the PCB traces are laid out, nut since the layout diagram
indicates that both stages are enclosed by (metal?) shields, it would be
possible that the PCB trace(s) that connect the shields together might be
intermittently broken fron the rest of the circuit. That would cause the
symptom of the measured B and E voltages being high negative, indicating
that the collector circuits of both stages are open. Look for a broken trace
or solder joint somewhere in the collector circuits.

I've seen broken shielding enclosure connections cause all sorts of weird
symptoms.
--
Dave M
A woman has the last word in any argument. Anything a man says after that is
the beginning of a new argument.

[Franc Zabkar]

On Mon, 05 Mar 2012 15:39:48 -0800, Winston <Win...@Bigbrother.net>

put finger to keyboard and composed:

>Franc Zabkar wrote:
>
>(...)
>
>> As for R22, I don't understand how an open circuit could reduce the
>> voltage on the base of the transistor.
>
>
>Emitter current through R24 is adjusted by the setting of
>R22, per the note to the right of R24. As R22 is adjusted
>higher in resistance, we can expect less current to flow
>from the base to emitter, causing AF126 to tend towards
>cutoff. (The base becomes less negative *in relation to
>the emitter*).

AISI, the voltage readings on the circuit diagram are using the
positive terminal of the 9V battery as the 0V reference. Therefore all
the voltage measurements are negative numbers, which means that the
transistor is being turned on harder during the fault condition. The
voltage on circuit ground would be -9V.

Or am I having a brain fart? (Quite likely)

[Sylvia Else]

> Voltage readingso

> Test point Radio working: Radio not working
> ------------------- --------------------
> -------------------------
> E. AF178 -1.10V -1.20V
> B. AF178 -1.50V -1.50V
> E. AF124 -1.10V -1.20V
> B. AF124 -1.32V -1.44V
> E. AF121 -0.85V -0.90V
> B. AF121 -1.20V -1.30V
> E. AF126 (1) -1.00V -3.70V *
> B. AF126 (1) -1.20V -4.00V *
> E. AF126 (II) -0.80V -3.70V *
> B. AF126 (II) -1.10V -3.60V *
> E. AC151 (I) - 0.90V -0.80V
> C. AC151 (I) --3.05V -2.95V
> E. AC151 (II) --0.66V -0.62V
> C. AC151 (II) --3.20V -3.10V
>
> Thanks once again for looking. Lenny

The bias of AF126 II is derived from the emitter of AF126 I (hereinafter
'the transistor'), so if the latter's bias arangements go awry, so will
the former's, which is thus of no interest.

If pin 10 of F IV became open circuit, the base of the transistor would
be pulled towards -9V through R5, R4, R26 and R21 in series, being a
total of 47.2K. For that to put the base at -4V requires a base current
of 0.1mA, there being no other source for the current.

For the emitter of the transistor to be at -3.7V requires a current of
4.5mA through R24 (the 820 ohm resistor). Given the calculated base
current, this would be the case if the beta of the transistor were 42,
which seems entirely plausible.

So if the transistor has a beta of around 40, the behaviour can be
explained by an intermittent open circuit at, or in the vicinity of, pin
10 of F IV.

Sylvia.

[Winston]

Franc Zabkar wrote:

(...)

> AISI, the voltage readings on the circuit diagram are using the
> positive terminal of the 9V battery as the 0V reference. Therefore all
> the voltage measurements are negative numbers, which means that the
> transistor is being turned on harder during the fault condition. The
> voltage on circuit ground would be -9V.
>
> Or am I having a brain fart? (Quite likely)

I had the fart. :)

You and Sylvia are much closer to the truth.
I now see that R5, R4, R28 and R21 would tend to turn on
the transistor (AF126 I) if the path from the positive
terminal of the battery, (through the diode "1.4 St1",
through pin 10 of F IV) were opened, because pin 10
of F IV is only one diode drop less than
the positive terminal of the battery normally.

So, I retract my diagnosis and now think that pin 10
of F IV and both pins of diode "1.4 Stl" should be
cleaned and re-soldered.

--Winston

[Winston]

Yes, I now see that R5, R4, R28 and R21 would tend to turn on the transistor if the
path to pin 10 of F IV were interrupted.

> being a total of 47.2K. For that to put the base at -4V requires a base current of 0.1mA, there being no
> other source for the current.
>
> For the emitter of the transistor to be at -3.7V requires a current of 4.5mA through R24 (the 820 ohm resistor). Given
> the calculated base current, this would be the case if the beta of the transistor were 42, which seems entirely plausible.
>
> So if the transistor has a beta of around 40, the behaviour can be explained by an intermittent open circuit at, or in
> the vicinity of, pin 10 of F IV.

I agree. Cleaning and re-soldering pin 10 of F IV as well as both pins of
the diode "1.4 St1" are good next steps.

--Winston

[Franc Zabkar]

On Tue, 06 Mar 2012 06:40:59 -0800, Winston <Win...@Bigbrother.net>

put finger to keyboard and composed:

>So, I retract my diagnosis and now think that pin 10
>of F IV and both pins of diode "1.4 Stl" should be
>cleaned and re-soldered.

AISI, if the diode were open, then that would disturb the bias on the
preceding stages (AF121 and AF124/125).

[Jon Elson]

klem kedidelhopper wrote:


> The strange thing is that when powering this radio up again after a
> shut down, the time it remains on before it quits once again is
> directly proportional to the time that it has been off.

OK, this HAS to be a bad electrolytic capacitor. That is the only component
that has that sort of memory. Replace electrolytics in the area where
the problem is suspected. They are often used in bias networks.

Jon

[Sylvia Else]

As Frank observes, if the 1.4 St1 connections are compromised, then the
bias for the AF124 would be affected, and on the OP's readings, it is not.

Now, we don't know the nature of the link between that diode and pin ten
of F IV, and I've seen Grundig do some rather questionable things, but
if it's just a circuit board track, the fault pretty much has to lie
either in the pin 10 soldering, or in the track itself.

Sylvia.

[Winston]

Sylvia Else wrote:
> On 7/03/2012 1:46 AM, Winston wrote:
>> Sylvia Else wrote:
>>> On 5/03/2012 2:47 PM, klem kedidelhopper wrote:

(...)

>>>> http://dl.dropbox.com/u/65394789/Grundig%20large%20schematic.pdf
>>>>
>>>> Voltage readingso
>>>> Test point Radio working: Radio not working
>>>> ------------------- --------------------
>>>> -------------------------
>>>> E. AF178 -1.10V -1.20V
>>>> B. AF178 -1.50V -1.50V
>>>> E. AF124 -1.10V -1.20V
>>>> B. AF124 -1.32V -1.44V
>>>> E. AF121 -0.85V -0.90V
>>>> B. AF121 -1.20V -1.30V
>>>> E. AF126 (1) -1.00V -3.70V *
>>>> B. AF126 (1) -1.20V -4.00V *
>>>> E. AF126 (II) -0.80V -3.70V *
>>>> B. AF126 (II) -1.10V -3.60V *
>>>> E. AC151 (I) - 0.90V -0.80V
>>>> C. AC151 (I) --3.05V -2.95V
>>>> E. AC151 (II) --0.66V -0.62V
>>>> C. AC151 (II) --3.20V -3.10V
>>>>
>>>> Thanks once again for looking. Lenny

(...)

> As Frank observes, if the 1.4 St1 connections are compromised, then the bias for the AF124 would be affected, and on the
> OP's readings, it is not.
>
> Now, we don't know the nature of the link between that diode and pin ten of F IV, and I've seen Grundig do some rather
> questionable things, but if it's just a circuit board track, the fault pretty much has to lie either in the pin 10
> soldering, or in the track itself.

Good point.

I look forward to what Lenny eventually discovers.

Given the history of the radio, a cracked trace
would not be out of the question.

It'll be amusing if it was C4 or C38 or R22 that was
intermittently shorting, instead. :)

--Winston

[Sylvia Else]

I don't think those could cause the observed effects - they'd all pull
the transistor base down to -9V, near enough.

Sylvia.

[Winston]

I hope Lenny will get back to us with his findings.

:)

--Winston

[klem kedidelhopper]

First of all let me say thank you to everyone who has become involved
in my problem. It really is so nice to be a part of this community of
kind people who are willing to help one another. I truly appreciate
all your opinions and all the advice you've sent my way.

I have been working on this radio off and on since I posted this. This
morning the alarm clock (bedroom radio) went off at 5:45 as it does
every morning with soft classical music. As we gently awoke I looked
over and saw that it was the Grundig on my bench! It was FIXED and it
was WORKING! Imagine my big let down upon actually waking up a few
minutes later and realizing that I really was in my bed, I wasn't in
the shop, and it WASN'T the Grundig, GAH! This thing isn't driving me
insane, I think it already has. Now it's haunting my nights as well as
my days....

I would have agreed that the direct relationship between the time the
radio is unpowered to the time it stays on the next time it is powered
up would definitely point to an electrolytic, but so far I have not
found it. There actually aren't that many in the signal circuit. I did
replace C 44, not because it checked bad, but because it was
suggested. However replacing it had no affect. I monitored the 1.4V
zener during intermittent periods of go/no go and the voltage remained
at 1,4V. Eventually the radio quit completely for a spell and I
bridged the following resistors: R4, R5, R29, R27, R24, R26, R25, and
then after measuring the resistance of R22, in circuit, (it was 13K),
I bridged it with a 100K (not a conclusive test I know) but just to
see if there were any affect There was none. I did resolder R22 but
that was not it either. The voltage across R22 does fluctuate quite a
bit during intermittent periods but it is a large resistor so I would
expect that. However I'm not sure if 13K is whats in parallel with R22
and R22 is really open. I thought of pulling it but first I think that
I have an idea.

Since the voltage never was exactly where it should have been, (1.18V)
upon powering the radio on the next time I think I' ll see if I can
set Vr124 to exactly 1.18V and wait and see if that might make a
difference. For one thing it will prove if R22 is working at all, and
also if the bias point is that critical to turning these transistors
on when they shouldn't be on.
I 'm also starting to wonder about the small capacitors among these
resistors that have these voltage changes about them. I really hate to
just start replacing things but I don't see any other way at this
point. I wish there were a way to isolate the offending stage, but
with the voltage changing as it is I don't see how I would do that. I
think I've ruled out the above resistors but I'll have to start
somewhere. It also frustrates me that I can't get on the collector of
AF126II because it's inside a can, (FIV) and the can is soldered onto
the board. There is another electrolytic, (C4) inside FIV but I don't
think that is part of this.

Other than that there are the small caps in and around these two
circuits and of course the ones in the last IF can (FIII) and the
detector, (FIV). I tried small spot cold spraying again around the
suspect area and even into the IF cans and detector assembly, and that
yielded nothing. I'm pretty sure I've ruled out a mechanical
intermittent also. This definitely appears to be something breaking
down electrically. I'm also wondering about one of the IF cans,
(coils) opening up intermittently. Does anyone remember how the old
five tube radios would crackle when the IF cans failed in them. I
never really knew how the cans were failing. We just replaced them and
that fixed the crackling. It occurred to me that if either coil in the
can in this radio opened up it would affect both AM and FM. I don't
recall if I mentioned it too but all the transistor can connections
have been lifted to rule out whiskers as well. .

I didn't get to work on the radio today and probably won't be able to
tomorrow either as work, (the kind you get paid for) has to take
precedence over my hobby. Although my "hobby" as of late has seemed to
be more like my nemesis to be exact. Thanks once again for all your
input. Lenny

[Winston]

klem kedidelhopper wrote:

(...)

> I didn't get to work on the radio today and probably won't be able to
> tomorrow either as work, (the kind you get paid for) has to take
> precedence over my hobby. Although my "hobby" as of late has seemed to
> be more like my nemesis to be exact. Thanks once again for all your
> input. Lenny

Did you happen to re-solder F IV pin 10 and
inspect the associated trace, Lenny?

I think Sylvia made a good point about it.

It would be hugely amusing to measure the voltage dropped
across R21 and R28 during functional / non-functional
circumstances. You could use them as current sense resistors
to point you in the direction of the open or short.

--Winston

[Franc Zabkar]

On Wed, 07 Mar 2012 20:35:40 -0800, Winston <Win...@Bigbrother.net>

put finger to keyboard and composed:

>Did you happen to re-solder F IV pin 10 and
>inspect the associated trace, Lenny?
>
>I think Sylvia made a good point about it.

I agree. I'm convinced she's pinpointed the culprit.

[klem kedidelhopper]

On Mar 7, 11:35 pm, Winston <Wins...@Bigbrother.net> wrote:
> klem kedidelhopper wrote:
>
> (...)
>
> > I didn't get to work on the radio today and probably won't be able to
> > tomorrow either as work, (the kind you get paid for) has to take
> > precedence over my hobby. Although my "hobby" as of late has seemed to
> > be more like my nemesis to be exact. Thanks once again for all your
> > input. Lenny

> T

> Did you happen to re-solder F IV pin 10 and
> inspect the associated trace, Lenny?
>
> I think Sylvia made a good point about it.
>
> It would be hugely amusing to measure the voltage dropped
> across R21 and R28 during functional / non-functional
> circumstances. You could use them as current sense resistors
> to point you in the direction of the open or short.
>
> --Winston

I know she was and it made perfect sense, but I was all over pin 10
and it's associated resistors. I had FIV out to replace AF126II in
fact and reinstalled it. I can't see anything wrong with the trace or
any traces for that matter. Tomorrow I'm going to take another look at
this. I'm going to check those two voltage drops, go and no go as you
suggested and I'll let you know. Lenny

[Winston]

Good.

I will Watch This Space. :)

--Winston

[spamtrap1888]

Sylvia must mean R28 in series; R26 goes from the emitter of AF 126 I
to ground.

A reference I found says that the minimum hFE for the AF 126 is 50, so
a beta of 42 here is kind of sad.

http://alltransistors.com/transistor.php?transistor=21733

Now I'm wondering if the supply voltage is really 9V.

[klem kedidelhopper]

Today I took the time to thoroughly clean all the old caked on flux
off the areas that I've been working on and others also in order to
get a better look at the board. I removed R22 and it tested OK. I put
it back and reset the bias on the emitter of AF126 I to exactly 1.18V
With this bias all the other voltages seem to be very close to what's
shown on the schematic as well. I also did reflow some other suspect
solder connections using Kester mildly activated liquid flux. I
measured the following voltages before it became very intermittent
again. Group 1 is with the radio working.. Group 2 is after the radio
became very intermittent.
group1:
Vr28 .078V
vr21 .012V
Vr29 .0067V
Vr22 5.80V
Vr26 5.41V
Vr25 .057V

group 2
Vr28 2.00V
Vr21 2.10V
Vr29 .0011V
Vr22 2.30V
Vr26 2.60V
Vr25 .105V

I don't know if this was a coincidence or what but I had taken the
above sets of voltages and had then decided to try to measure the E -
C voltage on AF126 I. As soon as I placed my probe on the collector I
must have detuned the circuit as the radio completely quit. I removed
the probe, it began working again briefly and then it started
crackling and soon after became constantly intermittent. Did I "shock"
something I wonder or was it just only a coincidence? Right now it's
in limbo between working and not, so intermittent that I can't really
look at anything.. Lenny

[amdx]

Have you tried heating the suspect transistors with the tip of your
soldering iron and dripping some freeze mist on them, and see what
changes. One at a time.
Also, you have several of the same model transistors in the circuit,
Swap them around!
Mikek

[klem kedidelhopper]

Well this may be a bit premature but in looking at the circuit I was
trying to determine what could possibly cause such a drastic change in
all these voltages, among the most drastic the voltage across R 22. So
on a whim I just replaced C38 and powered the radio up after a long
failure period. Normally under this condition it would quit almost
immediately. So far it has been working for about ten minutes. I hope
this doesn't end like my dream did the other morning....Lenny

[spamtrap1888]

On Mar 9, 2:18 pm, klem kedidelhopper <captainvideo462...@gmail.com>
wrote:

C38 was a foil cap, right? What kind did you replace it with?

[Winston]

It'd be great if C38 turned out to be our leaker, current-wise.

I'm still curious why the increased base current through
R21 (949 uA) is not completely apparent as an increased current in
the resistor that is in series with it, R28 (only 130 uA more,
not 949 uA more). Our increased current isn't going through R22
because during the failure, current through R22 *decreases*.

:)

Resistance Eworking Iworking Enotworking Inotworking Edifference Idifference
R28 15000 0.07800000 0.00000520 2.00000000 0.00013333 1.92200000 0.00012813
R21 2200 0.01200000 0.00000545 2.10000000 0.00095455 2.08800000 0.00094909
R29 330 0.00670000 0.00002030 0.00110000 0.00000333 -0.00560000 -0.00001697
R22 15000 5.80000000 0.00038667 2.30000000 0.00015333 -3.50000000 -0.00023333
R26 180000 5.41000000 0.00003006 2.60000000 0.00001444 -2.81000000 -0.00001561
R25 10000 0.05700000 0.00000570 0.10500000 0.00001050 0.04800000 0.00000480
R24 820 1.00000000 0.00121951 3.70000000 0.00451220 2.70000000 0.00329268

--Winston

[Sylvia Else]

You're right about the supply voltage. I just looked at the battery, but
in fact the radio takes its current from the battery through a resistor,
and the markings on the circuit indicate that this reduces the supply to
7.5V. Applying the correction gives a beta of 50.4, which is admittedly
still right at the low end of the spec you've found.

Offsetting that, the base is also being pulled down through R22, whose
actual value we don't know. I assumed it would be closer to 1M, on the
grounds that otherwise a smaller valued trimmer would have been used.

It's a bit moot, anyway, since the OP says that he's already resoldered
pin 10 of IF IV.

My next step would be to look at the voltage on what I think is pin 8 of
IF IV (i.e., the pin connected to R31 and R28.


Sylvia.

[klem kedidelhopper]

I used an epoxe cap.. The original was tubular and assuming foil with
a polarity stripe. It doesn't seem to matter though. I found R22 set
to about center when I pulled it. It measured about even on both sides
of the wiper. I probably turned it about 90 degrees after my first
adjustment for Vr24.(before replacing C38). But now I'm not so sure
that that all my readings are correct. If you look at the note on the
schematic it reads: "voltages measured with Grundig VTVM at battery
voltage 7.50V, "etc". This seems to suggest, and it was the
impression that I got that for whatever reason I was supposed to lower
the applied voltage to 7.50 V as measured at the battery terminals to
make my voltage measurements. Sylvia pointed out that (with the
positive ground arrangement) the applied voltage (negative) goes
through the 100 ohm resistor R46 to what we would consider as
"ground", the positive rail. This reverse polarity takes a bit of
getting used to...

There is a note near the battery connector which indicates what
appears to be a quiescent current between .020 and .022A. In fact when
I started this project I measured .025A on the bench power supply with
7.50V applied to the battery terminals. Therefore, given my initial
quiescent current reading, if all that current is indeed flowing
through R46 then I should have dropped 2.50V across R46. However I
never monitored that point so I didn't know. This morning the radio
was still working and I noted that Vr46 was .840V. Quiescent current
is still .025A. So now I'm really confused. Are you supposed to start
off with 9.0 Volts at the battery terminals for voltage measurement
purposes or is it 7.50 Volts? I can say with every certainty that with
7.50V applied the actual circuit voltages did almost mimic what the
schematic shows when the radio was operational. Or has my supply been
at least 1.50V - 2.50V too low throughout this experiment? Lenny

[klem kedidelhopper]

On Mar 10, 11:05 am, klem kedidelhopper <captainvideo462...@gmail.com>
wrote:

> ...
>
> read more »

[Winston]

klem kedidelhopper wrote:

(...)

> There is a note near the battery connector which indicates what
> appears to be a quiescent current between .020 and .022A. In fact when
> I started this project I measured .025A on the bench power supply with
> 7.50V applied to the battery terminals. Therefore, given my initial
> quiescent current reading, if all that current is indeed flowing
> through R46 then I should have dropped 2.50V across R46. However I
> never monitored that point so I didn't know. This morning the radio
> was still working and I noted that Vr46 was .840V. Quiescent current
> is still .025A. So now I'm really confused. Are you supposed to start
> off with 9.0 Volts at the battery terminals for voltage measurement
> purposes or is it 7.50 Volts? I can say with every certainty that with
> 7.50V applied the actual circuit voltages did almost mimic what the
> schematic shows when the radio was operational. Or has my supply been
> at least 1.50V - 2.50V too low throughout this experiment? Lenny

'Sounds like your 'rail voltage' ended up at 6.66 V considering
the 0.84 V drop in R46 or about 90 mV below the minimum indicated
on the schematic.

Were it me, I'd adjust the power supply until the rail voltage
measured, say 6.88 V.

It's an exercise anyway because you apparently found
and fixed the bug.

That's the important thing. :)

--Winston

[klem kedidelhopper]

Well I still have my fingers crossed but it does look hopeful. Lenny

[Sylvia Else]

On 11/03/2012 3:08 AM, klem kedidelhopper wrote:
> So now I'm really confused. Are you supposed to start
> off with 9.0 Volts at the battery terminals for voltage measurement
> purposes or is it 7.50 Volts? I can say with every certainty that with
> 7.50V applied the actual circuit voltages did almost mimic what the
> schematic shows when the radio was operational. Or has my supply been
> at least 1.50V - 2.50V too low throughout this experiment? Lenny

The situation mostly doesn't arise. With a few (possibly only one)
exceptions, the annotated voltages are between two specified points, not
a voltage relative to ground. Indeed, most are between two points
neither of which is anywhere near ground.

The base and emitter voltages are relative to the positive supply rail.
Given the way that the biases are obtained, they wouldn't have been
sensitive to the supply voltage, which is no doubt intentional given
that the supply voltage from a battery will change as the battery is
consumed.

On another note, while replacing C38 has apparently cured the problem,
I'm totally mystified as to why. It would imply that C38 had failed such
that it intermittently behaved as if it had a resistance of many
kilo-ohms in parallel with it. It seems an unlikely failure mode for a
capacitor.

Sylvia.

[Winston]

Sylvia Else wrote:

(...)

> On another note, while replacing C38 has apparently cured the problem, I'm totally mystified as to why. It would imply
> that C38 had failed such that it intermittently behaved as if it had a resistance of many kilo-ohms in parallel with it.
> It seems an unlikely failure mode for a capacitor.

C38 could be a total red herring.

Lenny said yesterday afternoon:

"I don't know if this was a coincidence or what but I had taken the
above sets of voltages and had then decided to try to measure the E -
C voltage on AF126 I. As soon as I placed my probe on the collector I
must have detuned the circuit as the radio completely quit."

It may just be that the base of AF 126 I is shorting out against
its grounded can, causing it to saturate intermittently.
If C38 is close to AF126 I, Lenny might have 'bumped' the short
open whilst replacing C38.

--Winston

[Sylvia Else]

If the base were shorted to the grounded can, then the base voltage
would be at ground level, but it's not. That's the puzzle with this
fault - finding a credible intermitten failure that will put the base at
the voltage level seen.

Sylvia.

[Sylvia Else]

On 6/03/2012 10:53 PM, Sylvia Else wrote:

> So if the transistor has a beta of around 40, the behaviour can be
> explained by an intermittent open circuit at, or in the vicinity of, pin
> 10 of F IV.

Belatedly, I realise that this cannot be correct. If pin 10 of F IV were
to become open circuit, there would be no sink for the current through
the diode 1.4 St1, and the bases of AF178 and AF124, and the latter
would rise to the positive rail.

I'm left wondering about the voltage on the collector of AF121. If it
turned out to be -4V (which seems a plausible enough operating point),
then there could be an intermittent short across the windings of FII,
thereby connecting the base of AF126 I more or less directly to the
collector of AF121.

Sylvia.

[klem kedidelhopper]

Given the intermittent nature of this job so far I have trouble
actually saying that it's repaired, However I now have two periods of
time wherein it has operated without a problem for at least 14 hours
continuously, with a few hours powered down in between. It's never
done that since this problem began. So I am starting to feel a bit
more certain about the validity of this repair.

I reset the bias to 1.18V yesterday and last night I noted that it had
drifted up to 1.23V. It's not a big excursion but I will keep an eye
on it though comparing initial turn on with after a few hours running
over the next couple of days or so.

There are a few things I still have to do. All the can grounds
are.currently unsoldered and disconnected from the circuit.
After I log some more time on this radio I'll need to restore those
and see if that makes any difference. I don't expect that it will but
I want to take this one step at a time.

The other thing I want to do is remove FIV one more time and put back
the transistor, (AF126 II) that was originally there. In actuality
that transistor is an AF124 which I purchased from Grundig service in
Manhattan about 35 years ago. The AF126 II was the problem with the
radio when I got it from a friend back around 1975 and not having a
126, Grundig substituted the 124 for me. It never seemed to affect the
alignment so I see no reason to not use it over again. The replacement
transistors that I have been using through out this repair came from a
friend in Sweden and are likely as old as my originals anyway.

So as it turns out I didn't need to replace any of them. Therefore the
alignment shouldn't have been affected, nor should the replacement of
C38 have affected the alignment much if at all either.

It occurred to me that if this were a customers radio, I'd likely own
their home at this point...

Lenny

[Winston]

Yup. You're right.

It almost must have been be an intermittently leaky C38.

--Winston

[Winston]

Were it me, I would move on to other things.

If the radio repeats the symptoms, then it wasn't an
intermittently leaky C38. At that point, I would
open the investigation once more.

Hey, it's working. Be happy. :)

>
> It occurred to me that if this were a customers radio, I'd likely own
> their home at this point...

More likely, they'd own your shop. :)

--Winston

[klem kedidelhopper]

So I've replaced all the original transistors, resoldered the
transistor cans, (grounds) and reset the bias with R22 to -1.18V with
7.50V applied to the battery connector. That bias voltage however
rises to -1.33V when the supply is boosted up to 9.0V. So as I
expected, it seems that the supply voltage does make a small
difference in bias. Does anyone else have any theories as to what
Grundig may have had in mind when they specified that bias as well as
the other circuit voltages? Was it with 7.50V applied or 9.0V? Lenny

[Winston]

klem kedidelhopper wrote:
> On Mar 11, 3:56 pm, Winston<Wins...@Bigbrother.net> wrote:

(...)

>> Were it me, I would move on to other things.
>>
>> If the radio repeats the symptoms, then it wasn't an
>> intermittently leaky C38. At that point, I would
>> open the investigation once more.
>>
>> Hey, it's working. Be happy. :)

(...)

> So I've replaced all the original transistors, resoldered the
> transistor cans, (grounds) and reset the bias with R22 to -1.18V with
> 7.50V applied to the battery connector. That bias voltage however
> rises to -1.33V when the supply is boosted up to 9.0V. So as I
> expected, it seems that the supply voltage does make a small
> difference in bias. Does anyone else have any theories as to what
> Grundig may have had in mind when they specified that bias as well as
> the other circuit voltages? Was it with 7.50V applied or 9.0V? Lenny

The way I read Grundig's schematic notes, they want us to set the
lab supply so that 7.0 V is seen on the power rail if in 'Medium Wave'
mode or 6.75 V on the rail if in 'FM' mode.

If that requires 7.8 V on the actual battery connector or 12.7 V
on the actual battery connector, it does not matter as long as the
rail voltage is set correctly for the function chosen.

They want the radio to function well with brand new batteries or
almost dead batteries.

I would not sweat over bias drift when a real battery is connected.
The documentation is pretty clear on their requirement.

--Winston

[josephkk]

After reading this thread through to this post i have a question. Can you
find the traces where R24 and R27 meet? I suspect a crack between there
and the + rail.

?-)

[Sylvia Else]

That wouldn't have the observed effect on the base and emitter voltages.

Sylvia.

[Sylvia Else]

There's a note on the schematic that they're measured with a battery
voltage of 7.5V. Using a vaccum tube volt-meter, which you might have
some difficulty obtaining now ;)

I'm surprised at the variation in bias with supply voltage. I would have
expected it to be quite insensitive.

Sylvia.

[Winston]

Sylvia Else wrote:
> On 12/03/2012 12:05 PM, klem kedidelhopper wrote:

(...)

>> Was it with 7.50V applied or 9.0V? Lenny
>
> There's a note on the schematic that they're measured with a battery voltage of 7.5V.

That looks like a typo.

R46 will drop 100 mV for every milliampere of battery current.

The only way to get the specified rail voltage of
7.0 V at 20 mA (Medium Wave operation) is with a
battery voltage of 9.0. Similarly, it takes 8.95 V
of battery voltage to get 6.75 V at 22 mA on
the rail, specified for FM operation.

> Using a vaccum tube volt-meter,
> which you might have some difficulty obtaining now ;)

I'm willing to believe that a modern multimeter is more
than sufficient for these measurements. My Fluke 189
has an input impedance of 10 M. I'm not too concerned
about the additional 82 nA it costs to use, for a 9 V measurement.

:)


--Winston

[William Sommerwerck]

I'm guessing that the 7.5V specs are for the lowest voltage the designers
felt gave acceptable performance.

Regardless, the important thing is the /relative/ voltages on a device's
terminals.

The base-emitter junction is forward-biased, about 0.3V for Ge devices, 0.6V
for Si. The base-collector junction is reverse-biased.

[Winston]

William Sommerwerck wrote:
> I'm guessing that the 7.5V specs are for the lowest voltage the designers
> felt gave acceptable performance.

I feel that Grundig assumed the service person would connect
their bench supply between rail ground and 'battery +',
*not between 'battery -' and 'battery +'*.

Unfortunately, they call 'power rail voltage' and 'battery
voltage' the same thing. They are different by 2 V in MW mode!



--Winston

[William Sommerwerck]

"Winston" <Win...@Bigbrother.net> wrote in message
news:jjku9...@news6.newsguy.com...

> William Sommerwerck wrote:

>> I'm guessing that the 7.5V specs are for the lowest voltage
>> the designers felt gave acceptable performance.

> I feel that Grundig assumed the service person would connect
> their bench supply between rail ground and "battery +",

> not between "battery -" and "battery +".

> Unfortunately, they call "power rail voltage" and "battery voltage"

> aren't the same thing. They are different by 2V in the MW model.

While we're at it... It's perfectly normal for amplifier stages -- tube or
transistor, in any kind of device -- to be fed through a small resistor,
with a largish capacitor to ground. This "decouples" the stage from the
power supply, to prevent feedback. The resistor /is not/ present to reduce
the power-supply voltage.

[Winston]

William Sommerwerck wrote:
> "Winston"<Win...@Bigbrother.net> wrote in message
> news:jjku9...@news6.newsguy.com...
>> William Sommerwerck wrote:
>
>>> I'm guessing that the 7.5V specs are for the lowest voltage
>>> the designers felt gave acceptable performance.
>
>> I feel that Grundig assumed the service person would connect
>> their bench supply between rail ground and "battery +",
>> not between "battery -" and "battery +".
>
>> Unfortunately, they call "power rail voltage" and "battery voltage"

[the same thing. They are different by 2 V in MW mode! ]

>> aren't the same thing. They are different by 2V in the MW model.

Thanks for fixing that William, but that's not what I
said or meant.

The MW and FM models are the same radio model.

When testing in Medium Wave *mode* the radio
requires 7.5 V between system ground and the power rail and is
specified to draw ca 20 mA. In FM *mode*, the radio is specified
to draw ca 22 mA from that same 7.5 V rail.

This is *not* the same as a 'battery voltage' of 7.5 V.
Our friends at Grundig have the same phrase to describe
'rail voltage' and 'battery voltage', which are normally
ca ~2 V different on the 'return' side.

I now understand that it makes perfect sense to attach our service
supply between 'system ground' and 'power rail' so that the
'system ground' can be bonded to earth ground via the power
supply, for safety. This is not the same as attaching the
supply across the battery, however.

> While we're at it... It's perfectly normal for amplifier stages -- tube or
> transistor, in any kind of device -- to be fed through a small resistor,
> with a largish capacitor to ground.

Yup. In this case, they are decoupling the final audio
stage from the rest of the radio.

> This "decouples" the stage from the
> power supply, to prevent feedback. The resistor /is not/ present to reduce
> the power-supply voltage.

Yet it does, by about 2 V from the battery to power rail.

--Winston

[Winston]

Winston wrote:

(...)

> 'Sounds like your 'rail voltage' ended up at 6.66 V considering
> the 0.84 V drop in R46 or about 90 mV below the minimum indicated
> on the schematic.
>
> Were it me, I'd adjust the power supply until the rail voltage
> measured, say 6.88 V.

Mia Culpa! The specification on the schematic is not
a *range* of acceptable rail voltages, it is a declaration
that the rail voltage must be +7 V in MW mode or +6.75 V
in FM mode, (An inch to the right, they re-declare both
at 7.5 V on the rail!)

I'd go with 7.5 V between ground and the power rail.
I'd leave 'battery minus' floating.


--Winston

[klem kedidelhopper]

On Mar 12, 10:29 am, Winston <Wins...@Bigbrother.net> wrote:
> William Sommerwerck wrote:
> > "Winston"<Wins...@Bigbrother.net>  wrote in message

I was using my RCA Senior Voltohmyst in the beginning. It has either a
10 or 11M impedance, however I built it from a kit I think in 1964. So
being almost 50 years old it's calibration could have been suspect. I
then switched to my Fluke digital. In any case I found that the
readings on both were very close anyway. (I don't use the VTVM much
anymore unless I get an old tube set in here to work on).

My initial reading on R24 before I made any adjustments, with 7.50V
applied to the battery terminals was 1.00V. That voltage rose to
3.60V when C38 would fail. Remember, (after replacing C38) that I
noted an approximate .015 V rise in VR24 when I increased the supply
from 7.50V to 9.0V. Assuming the engineers meant for this voltage to
be set with 9.0V applied, then perhaps I was reading what would be a
perfect bias point (with 7.50V applied), as measured on VR24
initially. It would be nice to know for certain after such an
exercise, but at this point I doubt very much that even someone at
Grundig would be able to shed any further light on this. But then what
you're saying makes perfect sense too Winston. I'm just really
surprised at the ambiguity of the statement on the schematic. In any
event there seems to be an amount of latitude available here, and
given (and I'm assuming) that the radio appears to have been working
that way for many years, perhaps it's a waste of time to fret over .
015V. Maybe I'll set it somewhere in between, enjoy my radio once
again and step back into reality....That would make my wife, who has
failed to see the sense in fixing a 40 year old radio very happy
indeed. Lenny

[Winston]

They were great tools in their day.
I had a PACO and lusted after a Voltohmyst. :)
http://www.glowbug.nl/valve/Paco-V70.html

> My initial reading on R24 before I made any adjustments, with 7.50V
> applied to the battery terminals was 1.00V.

Yup. Grundig said "Battery Voltage" but they meant
"Rail Voltage". The two are different. By 2 V!

> That voltage rose to
> 3.60V when C38 would fail. Remember, (after replacing C38) that I
> noted an approximate .015 V rise in VR24 when I increased the supply
> from 7.50V to 9.0V. Assuming the engineers meant for this voltage to
> be set with 9.0V applied, then perhaps I was reading what would be a
> perfect bias point (with 7.50V applied), as measured on VR24
> initially. It would be nice to know for certain after such an
> exercise, but at this point I doubt very much that even someone at
> Grundig would be able to shed any further light on this.

I think we have the straight info. I bet the bias when
set with 7.5 V *on the rail* would not drift very much
at all when the radio is powered from a 9 V battery.

> But then what
> you're saying makes perfect sense too Winston. I'm just really
> surprised at the ambiguity of the statement on the schematic.

Someone should write a Grundig Schematic Decoder!

They do present a lot of information but it does take time
to digest the hieroglyphics in order to translate.

> In any
> event there seems to be an amount of latitude available here, and
> given (and I'm assuming) that the radio appears to have been working
> that way for many years, perhaps it's a waste of time to fret over .
> 015V.

I agree. It is probably as close as it needs to be.

> Maybe I'll set it somewhere in between, enjoy my radio once
> again and step back into reality....That would make my wife, who has
> failed to see the sense in fixing a 40 year old radio very happy
> indeed.

I agree. There are plenty of 40 year old electronics
to repair everywhere. You should be very pleased to
have your nifty radio back! :)

--Winston

[klem kedidelhopper]

On Mar 12, 11:59 am, klem kedidelhopper <captainvideo462...@gmail.com>
wrote:

Well I couldn't resist, so to take this a bit further I checked the
power supply supplied with the radio. It is rated at 9.00V .200A. The
no load voltage is 9.50V. With it connected to the radio and with the
radio playing softly its output drops to 9.25V. In looking at the
schematic again and rereading the statement a few more times I now do
believe that in spite of the ambiguity, the original intention was to
supply 7.50 V to the battery terminals, however reference all
adjustments and voltages to the positive side of C59, (system ground).
So I did that and set the bias on FM to -1.18V. (AF126 I E) I then
recorded the following voltages:

Voltage readings
Test point Radio working:
------------------- --------------------

E. AF178 -1.15V
B. AF178 -1.48V
E. AF124 -1.14V
B. AF124 -1.37V
E. AF121 -0.90V
B. AF121 -1.24V
E. AF126 (1) -1.18V
B. AF126 (1) -1.47V
E. AF126 (II) -1.14V
B. AF126 (II) -1.34V

The voltage across C59 is 6.65V
So now although the radio has been working fine on both AM and FM, I
notice that the first two stages are reading a bit high. I wonder if I
may have another leaky cap. I was looking at possibly C12, C19 and
C32. Assuming I haven't driven everyone nuts with this project yet I
wonder what is the general consensus with this new revelation is?
Lenny

[Winston]

klem kedidelhopper wrote:
> On Mar 12, 11:59 am, klem kedidelhopper<captainvideo462...@gmail.com>

(...)

> Well I couldn't resist, so to take this a bit further I checked the
> power supply supplied with the radio. It is rated at 9.00V .200A. The
> no load voltage is 9.50V. With it connected to the radio and with the
> radio playing softly its output drops to 9.25V. In looking at the
> schematic again and rereading the statement a few more times I now do
> believe that in spite of the ambiguity, the original intention was to
> supply 7.50 V to the battery terminals, however reference all
> adjustments and voltages to the positive side of C59, (system ground).
> So I did that and set the bias on FM to -1.18V. (AF126 I E) I then
> recorded the following voltages:

Here, I added a Vnom column.

> Voltage readings
> Test point Radio working: Nominal V
> ------------------- ---------- -----------
>
> E. AF178 -1.15V -0.85
> B. AF178 -1.48V -1.15
> E. AF124 -1.14V -0.94
> B. AF124 -1.37V -1.12
> E. AF121 -0.90V -0.85 (MW) -0.60 (FM)
> B. AF121 -1.24V -1.05 (MW) -0.95 (FM)
> E. AF126 (1) -1.18V -1.18 (MW) -1.15 (FM)
> B. AF126 (1) -1.47V -1.45 (MW) -1.4 (FM)
> E. AF126 (II) -1.14V -1.05 (MW) -1.0 (FM)
> B. AF126 (II) -1.34V -1.33 (MW) -1.0 (FM)

>
> The voltage across C59 is 6.65V

You are testing at Vrail = 6.65 V?

Grundig says "don't bother warming up the VTVM unless
Vrail ==7.5 V" ( I heard them. Really I did. :)

> So now although the radio has been working fine on both AM and FM, I
> notice that the first two stages are reading a bit high. I wonder if I
> may have another leaky cap. I was looking at possibly C12, C19 and
> C32.

The little 'K' symbol next to these three apparently
denotes a ceramic cap. These 500 V units could become
extremely leaky at < 2 V I suppose.

I wouldn't bet that way, however.


There are lots more things that need your attention more
than your beloved radio. Personally, I think that at this
rate, in another 30 days, you will become borderline
obsessive. :)

My advice: Button it up and listen to it while doing one or more:

Clean or replace the sacrificial anode in your water heater

Do an oil change on your car

Flush and fill your car radiator

Rotate your tires

Replace the transmission fluid in your car
(Clean your funnel and flush with clean ATF first!)

Grab a basket and fill it with stuff from the back seat
and trunk. Neatly put away, toss or donate the contents
of the basket.

Shampoo car carpets

Diagnose that rattle in your clothes dryer

Vacuum out your dryer exhaust vent

Clean your gutters

Replace clogged rafter end vents with new ones

Replace the nasty 'wiring' job in the garage with
real Romex or conduit as code permits.

Install a chimney - mount 'Over The Air' antenna and cancel
your cable TV subscription

Scavenge stuff out of one room or garage that you
honestly will never need and give it to your local
Freecycler

Buy a little microcontroller board and teach yourself
assembly language. Make a robot.

etc. etc. :)


--Winston

[klem kedidelhopper]

Wow! I'll never complain about my wife nagging me again. I think
you've covered everything. Lenny

[Winston]

klem kedidelhopper wrote:

(...)

> Wow! I'll never complain about my wife nagging me again. I think
> you've covered everything. Lenny

:)

--Winston<--Nag, whine, nag, nag, nag.

[klem kedidelhopper]

I never thought of myself as being obsessive compulsive. In fact I've
been contemplating that for months and have finally decided that I'm
not...

I put the radio together last night. I'm listening to it right now.
It's nice to be able to "see" my bench again, and be done with this
project. It seems to play fine on both bands, in spite of the slight
difference in readings on the front end. I'm not going to worry about
that or the exact bias point for that matter. I have all my notes and
that's a project for another day, (maybe). I'm grateful that it's
working, and so well, and for all the friends who've helped me along
the way.

You'll have to excuse me now though. I have to go build a garage, so
that I can clean it out. Thanks again to everyone.
Best regards, Lenny

PS. I'll let you know when the next Philco Predicta walks in here...

[Winston]

klem kedidelhopper wrote:
> On Mar 12, 8:19 pm, Winston<Wins...@Bigbrother.net> wrote:
>> klem kedidelhopper wrote:
>>
>> (...)
>>
>>> Wow! I'll never complain about my wife nagging me again. I think
>>> you've covered everything. Lenny
>>
>> :)
>>
>> --Winston<--Nag, whine, nag, nag, nag.
>
> I never thought of myself as being obsessive compulsive. In fact I've
> been contemplating that for months and have finally decided that I'm
> not...

Heh! Good one!

> I put the radio together last night. I'm listening to it right now.
> It's nice to be able to "see" my bench again, and be done with this
> project. It seems to play fine on both bands, in spite of the slight
> difference in readings on the front end. I'm not going to worry about
> that or the exact bias point for that matter. I have all my notes and
> that's a project for another day, (maybe). I'm grateful that it's
> working, and so well, and for all the friends who've helped me along
> the way.

Especially Sylvia and Franc that got you pointed in
the proper direction.

You are now the World Expert on the Grundig Transistor 305.
Congratulations!

> You'll have to excuse me now though. I have to go build a garage, so
> that I can clean it out. Thanks again to everyone.
> Best regards, Lenny
>
> PS. I'll let you know when the next Philco Predicta walks in here...

Hoo Boy. Cannot wait for that.

--Winston :)

[Michael A. Terrell]

Winston wrote:
>
> klem kedidelhopper wrote:
> ?
> ? PS. I'll let you know when the next Philco Predicta walks in here...

>
> Hoo Boy. Cannot wait for that.

They show up on news:rec.antiques.radio+phono from time to time.


--
You can't have a sense of humor, if you have no sense.

[josephkk]

On Mon, 12 Mar 2012 15:26:38 +1100, Sylvia Else <syl...@not.here.invalid>
wrote:

>
>>> There is a note near the battery connector which indicates what
>>> appears to be a quiescent current between .020 and .022A. In fact when
>>> I started this project I measured .025A on the bench power supply with
>>> 7.50V applied to the battery terminals. Therefore, given my initial
>>> quiescent current reading, if all that current is indeed flowing
>>> through R46 then I should have dropped 2.50V across R46. However I
>>> never monitored that point so I didn't know. This morning the radio
>>> was still working and I noted that Vr46 was .840V. Quiescent current
>>> is still .025A. So now I'm really confused. Are you supposed to start
>>> off with 9.0 Volts at the battery terminals for voltage measurement
>>> purposes or is it 7.50 Volts? I can say with every certainty that with
>>> 7.50V applied the actual circuit voltages did almost mimic what the
>>> schematic shows when the radio was operational. Or has my supply been
>>> at least 1.50V - 2.50V too low throughout this experiment? Lenny
>>
>> After reading this thread through to this post i have a question. Can you
>> find the traces where R24 and R27 meet? I suspect a crack between there
>> and the + rail.
>>
>> ?-)
>
>That wouldn't have the observed effect on the base and emitter voltages.
>
>Sylvia.

Please to explain just why. As i don't think any possible intermittent
failure of C38 will explain the voltages seen.

?-)

[Sylvia Else]

Such a crack would certainly stop the radio from working, but there
would be nothing left to pull the emitters positive. They'd go to
ground, pulled there through R26. That's not what the OP observed.

The loss of the emitter-base currents (those junctions now being reverse
biased) would cause the base voltages to drop somewhat, but not by
anything like the amounts seen.

I have my own doubts about C38, notwithstanding the OP's apparently
successful repair, but that's a separate issue.

Sylvia.

[Lloyd Carmel]

responding to
http://www.electrondepot.com/repair/grundig-am-fm-portable-transistor-305-troubleshooting-138324-.htm
, Lloyd Carmel wrote:
Lenny, you are my hero.

I recently had the same problem with my Grundig Transistor 305.

The same solution worked like a charm.

Lloyd

klem kedidelhopper wrote:

> I never thought of myself as being obsessive compulsive. In fact I've
> been contemplating that for months and have finally decided that I'm
> not...
>
> I put the radio together last night. I'm listening to it right now.
> It's nice to be able to "see" my bench again, and be done with this
> project. It seems to play fine on both bands, in spite of the slight
> difference in readings on the front end. I'm not going to worry about
> that or the exact bias point for that matter. I have all my notes and
> that's a project for another day, (maybe). I'm grateful that it's
> working, and so well, and for all the friends who've helped me along
> the way.
>
> You'll have to excuse me now though. I have to go build a garage, so
> that I can clean it out. Thanks again to everyone.
> Best regards, Lenny
>
> PS. I'll let you know when the next Philco Predicta walks in here...

--