Power transistor question...
Dave
hold. MIL would like it repaired if possible, and kept in storage in case
of another hurricane knocking out power and services like the last one did.
Upon opening it up I see a power transistor (2SB834) with signs of
overheating. My meter tells me that the E/B and B/C pn junctions are
switching at .574 and .572 volts, respectively. Am I missing the mark, or
does this sound a little low to others as well, as if the pn junctions have
been damaged? Its a few more minutes until my candy store opens, and
several hours before I'll be able to get by there, but to me, this
transistor souinds like a good candidate for replacement. Would appreciate
hearing what others think, if anyone cares to comment. Otherwise I'll bide
my time until I can prove the part one way or another. Just hope I don't
have to order the damn thing and wait a week.
Thanks for any comments...
Dave
Phil Allison
"Dave"
<
> Have a very small (5" screen) black and white TV that has lost its
> verticle hold.
** Verticle ???
It is not a faulty power transistor in the vertical output - or their
would be no pix at all.
> MIL would like it repaired if possible,
** MIL ?
Is there a fourth letter missing .....
> and kept in storage in case of another hurricane knocking out power and
> services like the last one did. Upon opening it up I see a power
> transistor (2SB834) with signs of overheating. My meter tells me that the
> E/B and B/C pn junctions are switching at .574 and .572 volts,
> respectively. Am I missing the mark, or does this sound a little low to
> others as well, as if the pn junctions have been damaged?
** Sounds normal to me.
> Its a few more minutes until my candy store opens, and several hours
> before I'll be able to get by there, but to me, this transistor souinds
> like a good candidate for replacement. Would appreciate hearing what
> others think, if anyone cares to comment. Otherwise I'll bide my time
> until I can prove the part one way or another. Just hope I don't have to
> order the damn thing and wait a week.
** Loss of vertical HOLD is far more likely to be a fault in the small
signal circuitry OR the power supply.
Can you still adjust the vertical frequency to get the picture viewable -
but rolling ?
The first thing to check is all the filter and coupling electros in the
vertical and PSU for the vertical.
You need an ESR meter or lotsa luck.
.... Phil
Michael A. Terrell
Is the TV capable of receiving digital TV? If not, you'll need a
converter and a way to power it.
<http://www.geeks.com/details.asp?invtid=HLT71&cat=TVS&cpc=APM> is a
digital battery powered 7" handheld TV with a whip antenna and the
charger for $50 + shipping. This would be a better solution. Just
charge the battery once in a while and it'll be ready in an emergency.
--
It's easy to think outside the box, when you have a cutting torch.
Dave M
Phil is correct. The vertical output isn't likely to be the problem. Look
specifically in the sync separator and vertical oscillator areas for your
problem. The vertical oscillator isn't being locked to the vertical sync
pulses. That's why the picture is rolling.
Of course, the first thing to check is the power supply voltages and ripple
in those circuit areas. Clean power is essential to proper operation of any
circuit.
--
David
dgminala at mediacombb dot net
Dave
"Phil Allison" <phi...@tpg.com.au> wrote in message
news:94ceig...@mid.individual.net...
>
> "Dave"
> <
>> Have a very small (5" screen) black and white TV that has lost its
>> verticle hold.
>
> ** Verticle ???
Whatever...
> It is not a faulty power transistor in the vertical output - or their
> would be no pix at all.
Yeah, hadn't thought of it that way. See comments further down.
>> MIL would like it repaired if possible,
>
> ** MIL ?
>
> Is there a fourth letter missing .....
>
Mother-In-Law. No fourth letter.
>> and kept in storage in case of another hurricane knocking out power and
>> services like the last one did. Upon opening it up I see a power
>> transistor (2SB834) with signs of overheating. My meter tells me that
>> the E/B and B/C pn junctions are switching at .574 and .572 volts,
>> respectively. Am I missing the mark, or does this sound a little low to
>> others as well, as if the pn junctions have been damaged?
>
> ** Sounds normal to me.
>
>> Its a few more minutes until my candy store opens, and several hours
>> before I'll be able to get by there, but to me, this transistor souinds
>> like a good candidate for replacement. Would appreciate hearing what
>> others think, if anyone cares to comment. Otherwise I'll bide my time
>> until I can prove the part one way or another. Just hope I don't have to
>> order the damn thing and wait a week.
>
> ** Loss of vertical HOLD is far more likely to be a fault in the small
> signal circuitry OR the power supply.
>
> Can you still adjust the vertical frequency to get the picture viewable -
> but rolling ?
>
Yes, but the picture is only half the size of the screen at that point.
Attempts to adjust the vertical hold so as to enlarge the picture result if
more rolling. The 100K pot has to be maxed out to make it stop, and once it
is no longer totally maxed it starts rolling again. Thinking of stuffing
another 20K resistor in there to see if that changes anything...
> The first thing to check is all the filter and coupling electros in the
> vertical and PSU for the vertical.
>
> You need an ESR meter or lotsa luck.
>
Guess I'll need lotsa luck. What does an ESR meter actually measure,
pray tell?
Thanks again. Have been running all day and am just now coming to the end
of it all.
Dave
>
> .... Phil
>
>
>
>
Phil Allison
"Dave"
"Phil Allison"
>
>> The first thing to check is all the filter and coupling electros in the
>> vertical and PSU for the vertical.
>>
>> You need an ESR meter or lotsa luck.
>>
> Guess I'll need lotsa luck. What does an ESR meter actually measure,
> pray tell?
** It will tell you if an electro cap has or is about to die of old age.
Does this by measuring its internal resistance or ESR independent of actual
cap value in microfarads.
ESR = Equivalent Series Resistance.
http://en.wikipedia.org/wiki/Equivalent_series_resistance#Capacitors
.... Phil
Ken
Phil Allison
"Ken"
"Phil Allison"
> "Dave"
>> "Phil Allison"
>> >
>> >> The first thing to check is all the filter and coupling electros in
>> >> the
>> >> vertical and PSU for the vertical.
>> >>
>> >> You need an ESR meter or lotsa luck.
>> >>
>> > Guess I'll need lotsa luck. What does an ESR meter actually measure,
>> > pray tell?
>>
>> ** It will tell you if an electro cap has or is about to die of old age.
>>
>> Does this by measuring its internal resistance or ESR independent of
>> actual
>> cap value in microfarads.
>>
>> ESR = Equivalent Series Resistance.
>>
>> http://en.wikipedia.org/wiki/Equivalent_series_resistance#Capacitors
>>
>
> http://www.peakelec.co.uk/acatalog/jz_esr70.html
** Looks very nice.
Such ESR meters can also measure the ESR of cells, both rechargeable and
non-rechargeable types -the very low test current means they can check
Lithium button cells too.
The ESR of non-rechageables is good guide to remaining capacity - far
better than voltage is.
The ESR of a NiCd or NiMH cell is a good guide to its heath and ability to
deliver high currents.
Egs:
AA alkaline = 0.1 ohms new, rising to about 2 ohms at end of life.
AA carbon/zinc = 0.5 ohms new, rising to 5 ohms at end of life.
AA NiCd or NiMH = 0.03 ohms new, rising to 0.5 ohms at end of useful
life.
9V volt alkaline = 0.8 ohms new, rising to 10 ohms at end of life.
Lithium button cell ( ie CR2032 ) = 10 to 15 ohms new, rising to 50 ohms
at end of life.
.... Phil
Dave
Thank you Ken, and Phil. I had no idea. Definitely want one of those.
Much appreciated.
So anyway, if my voltages look good and there's no serious ripple anywhere,
I'm thinking more and more about the electro caps, but really don't fancy
pulling each and every one out to test without having some sort of strategy
as to which to test first. Any ideas on that? Larger ones first? What
would you guys do? I truly do appreciate the help and ideas.
Dave
Phil Allison
"Dave"
>
> Thank you Ken, and Phil. I had no idea. Definitely want one of those.
> Much appreciated.
>
> So anyway, if my voltages look good and there's no serious ripple
> anywhere, I'm thinking more and more about the electro caps, but really
> don't fancy pulling each and every one out to test without having some
> sort of strategy as to which to test first. Any ideas on that? Larger
> ones first? What would you guys do? I truly do appreciate the help and
> ideas.
>
** OK - the " old school " way of doing this tedious task was to briefly
parallel any suspect electo with a similar value and voltage cap while the
set is operating.
And see WTF happens.
TV service was never a game for the faint hearted..............
.... Phil
Dave
"Dave" <db5...@hotmail.com> wrote in message
news:N72dnaJJw6PhsH_Q...@posted.internetamerica...
Now believe I already have an ESR meter, though I didn't realize that was
one of its functions. What I have is an Extech 380193 LCR meter, which
tells me that a fairly new but run of the mill 1uF electrolytic cap out of
my junkbox has 12.5 Ohms of resistance. If I were to try to use this to
measure the caps in-circuit, how should I proceed? I am guessing that
discharging the cap before touching my test leads to the solder pads would
give me a reading, but I really hesitate to do this without some sort of
suggestion that such is a safe proceedure for my meter. Am guessing that
readings in the single digits indicate a defective device. Does this sound
reasonable? No power to the circuit under test, of course, and likely will
push in the power button a few minutes before beginning. Again, any advice
is appreciated.
Thanks,
Dave
Phil Allison
"Dave"
> Now believe I already have an ESR meter, though I didn't realize that was
> one of its functions. What I have is an Extech 380193 LCR meter, which
> tells me that a fairly new but run of the mill 1uF electrolytic cap out of
> my junkbox has 12.5 Ohms of resistance. If I were to try to use this to
> measure the caps in-circuit, how should I proceed? I am guessing that
> discharging the cap before touching my test leads to the solder pads would
> give me a reading, but I really hesitate to do this without some sort of
> suggestion that such is a safe proceedure for my meter. Am guessing that
> readings in the single digits indicate a defective device. Does this
> sound reasonable? No power to the circuit under test, of course, and
> likely will push in the power button a few minutes before beginning.
> Again, any advice is appreciated.
** Seen this ??
http://www.youtube.com/watch?v=zEA5MfllPdg
All you need to do is compare the ESR reading of a known good electro of
about the same ratings and size with the one under test. If the one under
test has say 5 times more ESR - it is useless or about to fail.
Often, with worn out electros, the ESR may be over 100 ohms.
.... Phil
Dave
No, I haven't seen that before. *Thank you.* Need to check and see if they
have any others I could use. Am continually amazed by what I find available
on youtube.
Is there anything special you know about testing a cap in-circuit with a
meter like this? Am still a little worried about maybe damaging my LCR
meter. It was a Christmas/Anniversary/Birthday gift from my loving wife
some 8 or 10 years ago, and would like to keep it in good working order.
Can't tell you how much I appreciate your help thus far with the subject at
hand...
Thanks again.
Dave
Phil Allison
"Dave"
> Is there anything special you know about testing a cap in-circuit with a
> meter like this? Am still a little worried about maybe damaging my LCR
> meter.
** Just make sure the electros are discharged - short them if in any doubt.
.... Phil
David
news:94h8ne...@mid.individual.net...
.... Phil
***
The meter being damaged is not a problem if things are
discharged. The other issue is will this meter give accurate
in-circuit readings? ESR meters use a very low AC voltage of
typically 100 mV, a frequency of 100 KHz or so, and a very low
source impedance to make the test. This minimizes the influence
of other circuitry in parallel with the capacitor on the
measurement. If your meter uses a higher voltage or places DC
bias across the capacitor, in-circuit test results may not be
accurate.
David
Jeff Liebermann
wrote:
>** Seen this ??
>http://www.youtube.com/watch?v=zEA5MfllPdg
Kills 9V batteries. Otherwise, good price and good unit with many
features that I'll never use.
>All you need to do is compare the ESR reading of a known good electro of
>about the same ratings and size with the one under test. If the one under
>test has say 5 times more ESR - it is useless or about to fail.
>
>Often, with worn out electros, the ESR may be over 100 ohms.
That will work, if you happen to have a known good and identical
capacitor handy. I have a fair collection of electroltyics but not
every value and voltage.
The problem with the Extech 380193 Handheld LCR meter is that it will
measure ESR at 120Hz and 1KHz. ESR is usually measured at about
100KHz. Dave Jones mentions this at about 12-13 minutes into his
video. This is because electrolytic cazapitors exhibit a minimum ESR
around 100Khz.
<http://www.amccaps.com/leaded-capacitors/switch-mode-ceramic-capacitors/esr-vs-frequency.html>
--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Meat Plow
Not a bad little meter for the $$$$. Anyone who does work on consumer
electronics ought to have one or something similar. Removes a lot of
guess work.
--
Live Fast Die Young, Leave A Pretty Corpse
Phil Allison
"Jeff Liebermann"
"Phil Allison"
>
> The problem with the Extech 380193 Handheld LCR meter is that it will
> measure ESR at 120Hz and 1KHz. ESR is usually measured at about
> 100KHz. Dave Jones mentions this at about 12-13 minutes into his
> video. This is because electrolytic cazapitors exhibit a minimum ESR
> around 100Khz.
> <http://www.amccaps.com/leaded-capacitors/switch-mode-ceramic-capacitors/esr-vs-frequency.html>
** Gotta pick you up on this one !!
That link shows ESR curves with frequency of a couple of * CERAMIC *
capacitors of unusually high values.
ESR meters intended for in circuit testing of electros by service techs
simply measure the cap's IMPEDANCE at around 100kHz. At this frequency -
all but the lowest value electros have their minimum impedances and the
values obtained are very close to ESR values at the same frequency. This
allows one to compare electros for (high frequency) ESR and pick out faulty
examples very easily.
OTOH, the Extech meter is designed to measure L and C values for a wide
range of inductors and capacitors and uses to standard test frequency of
1kHz as used in countless other instruments. This means it is NOT intended
to perform in-circuit testing of L and C value as other circuitry that may
be in parallel may spoil the readings.
However, in the case of electros with values from say 4.7 uF and upwards and
fitted to a TV set I would expect readings to be OK and the ESR values
obtained to be useable. It would be a good idea to re-test any electros
that are removed cos the ESR reading seemed high.
IMO - the 120 Hz frequency should only be used for out of circuit testing.
..... Phil
Phil Allison
"Meat Plow"
>> http://www.youtube.com/watch?v=zEA5MfllPdg
>
> Not a bad little meter for the $$$$. Anyone who does work on consumer
> electronics ought to have one or something similar. Removes a lot of
> guess work.
** I disagree.
An LCR meter is more useful for design and production than in servicing.
Many low cost DMMs include capacitance ranges that can measure from a few pF
up to 200 or 2000uF.
A dedicated ESR meter handles electros just fine while in circuit - and
lets you test all kinds of cells too, which an LCR meter often cannot.
Any DMM can read the resistance of an inductor or transformer winding.
The only function left is to measure inductors for value.
.... Phil
Jeff Liebermann
wrote:
>> The problem with the Extech 380193 Handheld LCR meter is that it will
>> measure ESR at 120Hz and 1KHz. ESR is usually measured at about
>> 100KHz. Dave Jones mentions this at about 12-13 minutes into his
>> video. This is because electrolytic cazapitors exhibit a minimum ESR
>> around 100Khz.
>> <http://www.amccaps.com/leaded-capacitors/switch-mode-ceramic-capacitors/esr-vs-frequency.html>
>That link shows ESR curves with frequency of a couple of * CERAMIC *
>capacitors of unusually high values.
Oops, y'er right. Sorry(tm).
Oddly, while the ESR of the ceramic caps are much lower than
electrolytics, the curve shapes seem to be similar.
Googling, I find:
<http://www.low-esr.com/esrfreqperfcurves.asp>
Note the dip in ESR and loss tangent at around 100KHz on various
graphs.
>ESR meters intended for in circuit testing of electros by service techs
>simply measure the cap's IMPEDANCE at around 100kHz. At this frequency -
>all but the lowest value electros have their minimum impedances and the
>values obtained are very close to ESR values at the same frequency. This
>allows one to compare electros for (high frequency) ESR and pick out faulty
>examples very easily.
>
>OTOH, the Extech meter is designed to measure L and C values for a wide
>range of inductors and capacitors and uses to standard test frequency of
>1kHz as used in countless other instruments. This means it is NOT intended
>to perform in-circuit testing of L and C value as other circuitry that may
>be in parallel may spoil the readings.
>
>However, in the case of electros with values from say 4.7 uF and upwards and
>fitted to a TV set I would expect readings to be OK and the ESR values
>obtained to be useable. It would be a good idea to re-test any electros
>that are removed cos the ESR reading seemed high.
>
>IMO - the 120 Hz frequency should only be used for out of circuit testing.
Yep. Agreed on all points.
>..... Phil
Phil Allison
"Jeff Liebermann"
"Phil Allison"
>
>>That link shows ESR curves with frequency of a couple of * CERAMIC *
>>capacitors of unusually high values.
>
> Oops, y'er right. Sorry(tm).
>
> Oddly, while the ESR of the ceramic caps are much lower than
> electrolytics, the curve shapes seem to be similar.
>
> Googling, I find:
> <http://www.low-esr.com/esrfreqperfcurves.asp>
> Note the dip in ESR and loss tangent at around 100KHz on various
> graphs.
** I see no such trend for the electros.
The ESR of most electros is almost constant down to about 500Hz, then rises
to a few times its high frequency value at 50Hz. I believe mobility of the
ions in the electrolyte is the cause.
Electros uniquely have very low Q factors - which means their impedance *
stays low * over a very wide frequency range.
A typical 470uF electro has an impedance under 0.1 ohms from 4kHz to 1MHz as
does the 330uF example in the graphs.
High Q capacitors ( film and ceramic) all have sharp impedance dips at self
resonance.
.... Phil
Dave
Wanted to thank *everyone* for the info and encouragement I have received in
this discussion. Bottom line for me, at least for now, is simply don't test
in-circuit (pop one lead and then test after discharging). Have also found
a ton of material on youtube and the net that convinces me to get a
dedicated ESR meter (or possibly build one.) Anyway, thanks all for a very
enlightening discussion.
Take it easy...
Dave
Phil Allison
"Dave"
>
> Wanted to thank *everyone* for the info and encouragement I have received
> in this discussion. Bottom line for me, at least for now, is simply don't
> test in-circuit (pop one lead and then test after discharging). Have also
> found a ton of material on youtube and the net that convinces me to get a
> dedicated ESR meter (or possibly build one.) Anyway, thanks all for a
> very enlightening discussion.
** This is the one I would buy - if I did not already have two of Bob's
earlier designs.
http://www.anatekcorp.com/blueesr.htm
BTW
Bob is an old mate of mine.
.... Phil
Jamie
I use a cheap B&K LCR, it does in circuit beautifully.
Jamie
Meat Plow
I'd like to see the meter described test at a higher frequency but other
than that I can't find much else wrong. I've been relying on an old Tenma
cap meter for years. It's gets you in the ball park. And there were
reliable repairs before LCR and ESR meters. I know, been at it from high
school back in 1970. These days I tend to shy away from anything I need
an ESR meter for. Plenty of vintage stuff out there that people like to
keep going.
Phil Allison
"Meat Plow"
>
> I'd like to see the meter described test at a higher frequency but other
> than that I can't find much else wrong. I've been relying on an old Tenma
> cap meter for years. It's gets you in the ball park. And there were
> reliable repairs before LCR and ESR meters. I know, been at it from high
> school back in 1970. These days I tend to shy away from anything I need
> an ESR meter for. Plenty of vintage stuff out there that people like to
> keep going.
** ESR meters are MOST useful with older equipment, particularly valve
amplifiers.
All those electros are old and have been running in a hot environment.
..... Phil
Dave
"Jamie" <jamie_ka1lpa_not_v...@charter.net> wrote in message
news:QVdFp.9148$rq2....@newsfe12.iad...
Hey Jamie, thanks for the note. So, how do you perform an in-circuit ESR
test on a suspect cap? Do you bother to discharge it, or do you just let
the circuitry around the cap do that? And how reliable are the numbers you
come up with? I tried to do an in-circuit test today on a cap and thought I
had gotten lucky with my first shot. A 10uF @ 100V cap gave me an ESR
reading of 42.15 in-circuit, but when I popped it out and tested it again it
dropped to 0.12. big difference! Still trying to figure out what I might
have been doing wrong...
Have since discovered a different cap that may actually be the problem. A
.22uF @ 50V cap with an ESR reading of 25+ ohms. Am thinking this component
may be where the vertical hold sync pulse gets lost, as it feeds an
oscillator/mixer transistor which feeds the output transistor of the
vertical hold circuitry. All of this two days after I discovered I had an
ESR meter and didn't know it. <shaking head>
Dave
Phil Allison
"Dave"
"Jamie
= Maynard A. Philbrook
= Lunatic, code scribbler & radio ham: KA1LPA
>
>> I use a cheap B&K LCR, it does in circuit beautifully.
>>
** Blatant lie.
> Hey Jamie, thanks for the note. So, how do you perform an in-circuit ESR
> test on a suspect cap?
** Jaime is a congenital bullshit artist.
Just IGNORE him.
> I tried to do an in-circuit test today on a cap and thought I had gotten
> lucky with my first shot. A 10uF @ 100V cap gave me an ESR reading of
> 42.15 in-circuit, but when I popped it out and tested it again it dropped
> to 0.12. big difference! Still trying to figure out what I might have
> been doing wrong...
** All that means is there is some resistance in parallel with the 10uF cap.
Any parallel resistance is computed to a misleading ESR number by an LCR
meter.
That's the problem.
With a dedicated ESR meter that measures the impedance of an electro at
100kHz, the effect of parallel resistors or diode junctions that may exist
is ignored.
.... Phil