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Odd Transistor Readings
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Cursitor Doom
Oct 25, 2019, 11:56:35 AM10/25/19
to
So I've had to pull 6 transistors one by one out of this amplifier board,
in the strong suspicion at least one of them was faulty. They all tested
fine - until the last one (typical!). Anyway, these are small signal PNP
BJTs in TO-8 tin cans. The last one checks out fine for base-emitter and
base-collector junctions giving about 650mV in one direction only on the
diode test setting - I very nearly didn't bother testing further at this
point, given it was looking increasingly futile. Anyway, for the sake of
completeness one last check across the C-E terminals and I got 295mV both
ways! Double checking on the resistance range confirmed 600 ohms between
C and E both ways. I've never known a BJT fail in *this* way. Has anyone
else?
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in the strong suspicion at least one of them was faulty. They all tested
fine - until the last one (typical!). Anyway, these are small signal PNP
BJTs in TO-8 tin cans. The last one checks out fine for base-emitter and
base-collector junctions giving about 650mV in one direction only on the
diode test setting - I very nearly didn't bother testing further at this
point, given it was looking increasingly futile. Anyway, for the sake of
completeness one last check across the C-E terminals and I got 295mV both
ways! Double checking on the resistance range confirmed 600 ohms between
C and E both ways. I've never known a BJT fail in *this* way. Has anyone
else?
--
This message may be freely reproduced without limit or charge only via
the Usenet protocol. Reproduction in whole or part through other
protocols, whether for profit or not, is conditional upon a charge of
GBP10.00 per reproduction. Publication in this manner via non-Usenet
protocols constitutes acceptance of this condition.
Phil Allison
Oct 25, 2019, 4:26:20 PM10/25/19
to
Cursitor Doom wrote:
-------------------
Checking C-E is a standard practice, cos it's a common failure when a transistor is over voltaged or over heated under load.
Commonly known as " punch through" or "second breakdown".
...... Phil
-------------------
>
> So I've had to pull 6 transistors one by one out of this amplifier board,
> in the strong suspicion at least one of them was faulty. They all tested
> fine - until the last one (typical!). Anyway, these are small signal PNP
> BJTs in TO-8 tin cans. The last one checks out fine for base-emitter and
> base-collector junctions giving about 650mV in one direction only on the
> diode test setting - I very nearly didn't bother testing further at this
> point, given it was looking increasingly futile. Anyway, for the sake of
> completeness one last check across the C-E terminals and I got 295mV both
> ways! Double checking on the resistance range confirmed 600 ohms between
> C and E both ways.
>
** See, all you need was a simple ohm meter test.
> So I've had to pull 6 transistors one by one out of this amplifier board,
> in the strong suspicion at least one of them was faulty. They all tested
> fine - until the last one (typical!). Anyway, these are small signal PNP
> BJTs in TO-8 tin cans. The last one checks out fine for base-emitter and
> base-collector junctions giving about 650mV in one direction only on the
> diode test setting - I very nearly didn't bother testing further at this
> point, given it was looking increasingly futile. Anyway, for the sake of
> completeness one last check across the C-E terminals and I got 295mV both
> ways! Double checking on the resistance range confirmed 600 ohms between
> C and E both ways.
>
Checking C-E is a standard practice, cos it's a common failure when a transistor is over voltaged or over heated under load.
Commonly known as " punch through" or "second breakdown".
...... Phil
Fred McKenzie
Oct 25, 2019, 4:35:38 PM10/25/19
to
In article <qov5uu$thh$1...@dont-email.me>,
That sounds like leakage to me. Did you measure C, B and E voltages
in-circuit?
I wonder if a coupling capacitor from the previous stage is leaking, and
it might have damaged that transistor?
Fred
Cursitor Doom <cu...@notformail.com> wrote:
> So I've had to pull 6 transistors one by one out of this amplifier board,
> in the strong suspicion at least one of them was faulty. They all tested
> fine - until the last one (typical!). Anyway, these are small signal PNP
> BJTs in TO-8 tin cans. The last one checks out fine for base-emitter and
> base-collector junctions giving about 650mV in one direction only on the
> diode test setting - I very nearly didn't bother testing further at this
> point, given it was looking increasingly futile. Anyway, for the sake of
> completeness one last check across the C-E terminals and I got 295mV both
> ways! Double checking on the resistance range confirmed 600 ohms between
> C and E both ways. I've never known a BJT fail in *this* way. Has anyone
> else?
CD-
> So I've had to pull 6 transistors one by one out of this amplifier board,
> in the strong suspicion at least one of them was faulty. They all tested
> fine - until the last one (typical!). Anyway, these are small signal PNP
> BJTs in TO-8 tin cans. The last one checks out fine for base-emitter and
> base-collector junctions giving about 650mV in one direction only on the
> diode test setting - I very nearly didn't bother testing further at this
> point, given it was looking increasingly futile. Anyway, for the sake of
> completeness one last check across the C-E terminals and I got 295mV both
> ways! Double checking on the resistance range confirmed 600 ohms between
> C and E both ways. I've never known a BJT fail in *this* way. Has anyone
> else?
That sounds like leakage to me. Did you measure C, B and E voltages
in-circuit?
I wonder if a coupling capacitor from the previous stage is leaking, and
it might have damaged that transistor?
Fred
Phil Allison
Oct 25, 2019, 4:56:28 PM10/25/19
to
Fred McKenzie wrote:
---------------------
It's direct coupled throughout.
Despite my advice, he failed to carry out basic ohm meter tests with the devices in circuit.
Folk pick their favourite replies here and pay the price for that.
.... Phil
---------------------
> >
> That sounds like leakage to me. Did you measure C, B and E voltages
> in-circuit?
>
> I wonder if a coupling capacitor from the previous stage is leaking, and
> it might have damaged that transistor?
>
** The OP is working on a scope horizontal sweep amplifier PCB.
> That sounds like leakage to me. Did you measure C, B and E voltages
> in-circuit?
>
> I wonder if a coupling capacitor from the previous stage is leaking, and
> it might have damaged that transistor?
>
It's direct coupled throughout.
Despite my advice, he failed to carry out basic ohm meter tests with the devices in circuit.
Folk pick their favourite replies here and pay the price for that.
.... Phil
Cursitor Doom
Oct 25, 2019, 5:36:59 PM10/25/19
to
On Fri, 25 Oct 2019 16:35:34 -0400, Fred McKenzie wrote:
> CD-
>
> That sounds like leakage to me. Did you measure C, B and E voltages
> in-circuit?
Yes, I did. They were all over place and not just for the transistor in
> CD-
>
> That sounds like leakage to me. Did you measure C, B and E voltages
> in-circuit?
question:
Q10: Vc +1.1v, Vb +0.5v, Ve +1.2v
Q9: Vc -3.2v, Vb +1.1v, Ve -1.34v(this is the faulty one)
Q8: Vc -3.8v, Vb -3.2v, Ve -3.9v
Q15: Vc -2v, Vb +0.11v, Ve +0.78v
Q14: Vc -7.74v, Vb -2v, Ve -1.34v
Q13: Vc +3.5v, Vb -7.74v, Ve -7v
I'm not sure if just Q9 alone being faulty could account for three other
transistors showing 'impossible' bias voltages: Q8 fully saturated; Q10
inverse Vbc; Q13 inverse Vbe - but with them all being inter-dependent as
a consequence of direct coupling, who knows?
> I wonder if a coupling capacitor from the previous stage is leaking, and
> it might have damaged that transistor?
down the fault. Here's the schematic:
https://yandex.com/collections/card/5db3651651aa90bd7e86a504/
Cursitor Doom
Oct 25, 2019, 5:40:52 PM10/25/19
to
On Fri, 25 Oct 2019 21:36:51 +0000, Cursitor Doom wrote:
Let's try and make that clearer:
Q10: Vc +1.1v, Vb +0.5v, Ve +1.2v
Q9: Vc -3.2v, Vb +1.1v, Ve -1.34v (this is the faulty one)
Let's try and make that clearer:
Q10: Vc +1.1v, Vb +0.5v, Ve +1.2v
Cursitor Doom
Oct 25, 2019, 9:12:44 PM10/25/19
to
On Fri, 25 Oct 2019 15:56:14 +0000, Cursitor Doom wrote:
Having checked for replies in google groups...
I did actually carry out in-circuit resistance checks with the board
unpowered using a meter capable of exceeding the 0.7v before removing
anything. It indicated discrepancies compared to an identical board in
the area around Q10, but not a specific enough area nor specific enough
discrepancies to be of use.
Having checked for replies in google groups...
I did actually carry out in-circuit resistance checks with the board
unpowered using a meter capable of exceeding the 0.7v before removing
anything. It indicated discrepancies compared to an identical board in
the area around Q10, but not a specific enough area nor specific enough
discrepancies to be of use.
Phil Allison
Oct 25, 2019, 9:25:05 PM10/25/19
to
Cursitor Doom wrote:
-------------------------
My post said to use an analogue ohm meter on the X1 range - nothing else works near as well, especially any DMM I know of.
The ohms reading found corresponds to millivolts and volts across the load - easily calibrated with a DVM and few resistors. I inked voltage numbers on the ohms scale of my meter 45 years ago.
Most importantly, such meters deliver up to 50mA into the load, making redundant any resistors that might be in parallel with device junctions.
Betcha you did nothing like that or else the near shorted C-E would have jumped up and bit you.
.... Phil
-------------------------
>
> Having checked for replies in google groups...
>
> I did actually carry out in-circuit resistance checks with the board
> unpowered using a meter capable of exceeding the 0.7v before removing
> anything.
>
** You are being very coy about what you REALLY did.
> Having checked for replies in google groups...
>
> I did actually carry out in-circuit resistance checks with the board
> unpowered using a meter capable of exceeding the 0.7v before removing
> anything.
>
My post said to use an analogue ohm meter on the X1 range - nothing else works near as well, especially any DMM I know of.
The ohms reading found corresponds to millivolts and volts across the load - easily calibrated with a DVM and few resistors. I inked voltage numbers on the ohms scale of my meter 45 years ago.
Most importantly, such meters deliver up to 50mA into the load, making redundant any resistors that might be in parallel with device junctions.
Betcha you did nothing like that or else the near shorted C-E would have jumped up and bit you.
.... Phil
Fred McKenzie
Oct 25, 2019, 9:53:02 PM10/25/19
to
In article <qovptj$thh$3...@dont-email.me>,
Diagram appears to have a mix of PNP and NPN transistors.
Fred
Cursitor Doom <cu...@notformail.com> wrote:
> It's all *direct* coupled, which is 9/10 of the problem in trying to pin
> down the fault. Here's the schematic:
>
> https://yandex.com/collections/card/5db3651651aa90bd7e86a504/
CD-
> It's all *direct* coupled, which is 9/10 of the problem in trying to pin
> down the fault. Here's the schematic:
>
> https://yandex.com/collections/card/5db3651651aa90bd7e86a504/
Diagram appears to have a mix of PNP and NPN transistors.
Fred
Phil Allison
Oct 25, 2019, 10:13:41 PM10/25/19
to
Fred McKenzie wrote:
---------------------
> >
> > https://yandex.com/collections/card/5db3651651aa90bd7e86a504/
>
> CD-
>
> Diagram appears to have a mix of PNP and NPN transistors.
>
>
** Hey - don't confuse the OP with facts !!
..... Phil
---------------------
> >
> > https://yandex.com/collections/card/5db3651651aa90bd7e86a504/
>
> CD-
>
> Diagram appears to have a mix of PNP and NPN transistors.
>
>
..... Phil
Trevor Wilson
Oct 25, 2019, 11:24:24 PM10/25/19
to
On 26/10/2019 2:56 am, Cursitor Doom wrote:
> So I've had to pull 6 transistors one by one out of this amplifier board,
> in the strong suspicion at least one of them was faulty. They all tested
> fine - until the last one (typical!). Anyway, these are small signal PNP
> BJTs in TO-8 tin cans. The last one checks out fine for base-emitter and
> base-collector junctions giving about 650mV in one direction only on the
> diode test setting - I very nearly didn't bother testing further at this
> point, given it was looking increasingly futile. Anyway, for the sake of
> completeness one last check across the C-E terminals and I got 295mV both
> ways! Double checking on the resistance range confirmed 600 ohms between
> C and E both ways. I've never known a BJT fail in *this* way. Has anyone
> else?
**Frequently. Invest in a PEAK transistor tester. It will save time and
> So I've had to pull 6 transistors one by one out of this amplifier board,
> in the strong suspicion at least one of them was faulty. They all tested
> fine - until the last one (typical!). Anyway, these are small signal PNP
> BJTs in TO-8 tin cans. The last one checks out fine for base-emitter and
> base-collector junctions giving about 650mV in one direction only on the
> diode test setting - I very nearly didn't bother testing further at this
> point, given it was looking increasingly futile. Anyway, for the sake of
> completeness one last check across the C-E terminals and I got 295mV both
> ways! Double checking on the resistance range confirmed 600 ohms between
> C and E both ways. I've never known a BJT fail in *this* way. Has anyone
> else?
heartache.
--
Trevor Wilson
www.rageaudio.com.au
--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
Ralph Mowery
Oct 25, 2019, 11:29:09 PM10/25/19
to
In article <h1hsj2...@mid.individual.net>, tre...@rageaudio.com.au
says...
component testers for about $ 15 to $ 25.
About the same as the Peak and one box tests solid state and passive
components where Peak sells 2 boxes to do the same thing.
says...
>
> **Frequently. Invest in a PEAK transistor tester. It will save time and
> heartache.
>
>
>
>
Instead of investing in the PEAK, go to ebay and get one of the
> **Frequently. Invest in a PEAK transistor tester. It will save time and
> heartache.
>
>
>
>
component testers for about $ 15 to $ 25.
About the same as the Peak and one box tests solid state and passive
components where Peak sells 2 boxes to do the same thing.
Phil Allison
Oct 25, 2019, 11:35:34 PM10/25/19
to
Trevor Wilson wrote:
-------------------
>
> ** Invest in a PEAK transistor tester.
---------------------------------------------
** Never used one - do they inject at least 25mA testing BJT junctions?
Useless in-circuit if they don't.
25mA will override even a 50ohm B-E resistor
... Phil
-------------------
>
> ** Invest in a PEAK transistor tester.
---------------------------------------------
** Never used one - do they inject at least 25mA testing BJT junctions?
Useless in-circuit if they don't.
25mA will override even a 50ohm B-E resistor
... Phil
Trevor Wilson
Oct 26, 2019, 2:11:03 AM10/26/19
to
On 26/10/2019 2:35 pm, Phil Allison wrote:
> Trevor Wilson wrote:
>
> -------------------
>
>>
>> ** Invest in a PEAK transistor tester.
>
> ---------------------------------------------
>
>
> ** Never used one - do they inject at least 25mA testing BJT junctions?
**Nope.
> Trevor Wilson wrote:
>
> -------------------
>
>>
>> ** Invest in a PEAK transistor tester.
>
> ---------------------------------------------
>
>
> ** Never used one - do they inject at least 25mA testing BJT junctions?
https://www.peakelec.co.uk/acatalog/dca75-dca-pro-semiconductor-analyser.html
12ma max.
>
> Useless in-circuit if they don't.
>
> 25mA will override even a 50ohm B-E resistor
DCA55 did let me down once). In fact, it has been able to show very
slight faults in some semiconductors, that multimeter tests did not reveal.
Trevor Wilson
Oct 26, 2019, 2:15:11 AM10/26/19
to
On 26/10/2019 2:29 pm, Ralph Mowery wrote:
> In article <h1hsj2...@mid.individual.net>, tre...@rageaudio.com.au
> says...
>>
>> **Frequently. Invest in a PEAK transistor tester. It will save time and
>> heartache.
>>
>>
>>
>>
>
> Instead of investing in the PEAK, go to ebay and get one of the
> component testers for about $ 15 to $ 25.
**I've used one. Impressive value for money.
> In article <h1hsj2...@mid.individual.net>, tre...@rageaudio.com.au
> says...
>>
>> **Frequently. Invest in a PEAK transistor tester. It will save time and
>> heartache.
>>
>>
>>
>>
>
> Instead of investing in the PEAK, go to ebay and get one of the
> component testers for about $ 15 to $ 25.
>
> About the same as the Peak and one box tests solid state and passive
> components where Peak sells 2 boxes to do the same thing.
https://www.peakelec.co.uk/acatalog/dca75-dca-pro-semiconductor-analyser.html
Note the ability to display curves on a computer.
Please point me to one that can do what the DCA75 does.
Phil Allison
Oct 26, 2019, 2:21:55 AM10/26/19
to
Trevor Wilson wrote:
--------------------
>
> > Useless in-circuit if they don't.
>
>
> **I don't trust in-circuit tests.
** Not even Bop Parker's magic ESR meter ?
Or if a junction shows open or short ?
Or a C-E test shows low ohms or near short ??
Shirley you jest ?
..... Phil
--------------------
> >
> >>
> >> ** Invest in a PEAK transistor tester.
> >
> > ---------------------------------------------
> >
> >
> > ** Never used one - do they inject at least 25mA testing BJT junctions?
>
> **Nope.
>
> https://www.peakelec.co.uk/acatalog/dca75-dca-pro-semiconductor-analyser.html
>
> 12ma max.
>
** Marginal then.
> >>
> >> ** Invest in a PEAK transistor tester.
> >
> > ---------------------------------------------
> >
> >
> > ** Never used one - do they inject at least 25mA testing BJT junctions?
>
> **Nope.
>
> https://www.peakelec.co.uk/acatalog/dca75-dca-pro-semiconductor-analyser.html
>
> 12ma max.
>
>
> > Useless in-circuit if they don't.
>
>
> **I don't trust in-circuit tests.
Or if a junction shows open or short ?
Or a C-E test shows low ohms or near short ??
Shirley you jest ?
..... Phil
Cursitor Doom
Oct 26, 2019, 5:42:07 AM10/26/19
to
On Sat, 26 Oct 2019 14:24:20 +1100, Trevor Wilson wrote:
> **Frequently.
Well I don't do repair work for a living so defer to your wider knowledge
of the subject. I just find it baffling how such a transistor can give
readings like those I described, with a Rc-e lower than each of its Rc-b
and Rb-e readings!
> Invest in a PEAK transistor tester. It will save time and
> heartache.
It wouldn't be worth if for the number of times a 'mass extraction' like
this has been necessary, which before this happened was zero.
It would be nice to have *all* the meters in the Peake range, but on an
occasional need basis I can't justify it.
> **Frequently.
Well I don't do repair work for a living so defer to your wider knowledge
of the subject. I just find it baffling how such a transistor can give
readings like those I described, with a Rc-e lower than each of its Rc-b
and Rb-e readings!
> Invest in a PEAK transistor tester. It will save time and
> heartache.
this has been necessary, which before this happened was zero.
It would be nice to have *all* the meters in the Peake range, but on an
occasional need basis I can't justify it.
Phil Allison
Oct 26, 2019, 6:16:28 AM10/26/19
to
Cursitor Doom wrote:
-------------------
Trevor Wilson wrote:
>
> > **Frequently.
>
>
> Well I don't do repair work for a living so defer to your wider knowledge
> of the subject. I just find it baffling how such a transistor can give
> readings like those I described, with a Rc-e lower than each of its Rc-b
> and Rb-e readings!
>
** Never seen a shorted power transistor ?
The two junctions test OK, but there is a near dead short from C to E.
If you open one, the chip usually has a black spot on it where the silicon has melted.
Your example involves a low resistance, likely the result of an over voltage or over current spike.
Mistreat a BJT and a short from C to E is the MOST likely outcome.
Same goes for mosfets, the short is then from D to S.
Seen many hundreds of both.
Diodes fail short too, plus zeners, triacs and SCRs.
Silicon dies are fragile things.
.... Phil
-------------------
Trevor Wilson wrote:
>
> > **Frequently.
>
>
> Well I don't do repair work for a living so defer to your wider knowledge
> of the subject. I just find it baffling how such a transistor can give
> readings like those I described, with a Rc-e lower than each of its Rc-b
> and Rb-e readings!
>
The two junctions test OK, but there is a near dead short from C to E.
If you open one, the chip usually has a black spot on it where the silicon has melted.
Your example involves a low resistance, likely the result of an over voltage or over current spike.
Mistreat a BJT and a short from C to E is the MOST likely outcome.
Same goes for mosfets, the short is then from D to S.
Seen many hundreds of both.
Diodes fail short too, plus zeners, triacs and SCRs.
Silicon dies are fragile things.
.... Phil
Cursitor Doom
Oct 26, 2019, 11:52:41 AM10/26/19
to
PITA having to cut and paste from Google Groups but anyway...
"** You are being very coy about what you REALLY did.
My post said to use an analogue ohm meter on the X1 range - nothing else
works near as well, especially any DMM I know of.
The ohms reading found corresponds to millivolts and volts across the
load - easily calibrated with a DVM and few resistors. I inked voltage
numbers on the ohms scale of my meter 45 years ago.
Most importantly, such meters deliver up to 50mA into the load, making
redundant any resistors that might be in parallel with device junctions.
Betcha you did nothing like that or else the near shorted C-E would have
jumped up and bit you. "
Nope. I actually used one of these:
https://www.ebay.co.uk/itm/Selectest-Testmeter-Dlll-Old-Multi-
Meter/333272931128?hash=item4d989d5b38:g:jD8AAOSwxGBdNGvF
Not the same exact model as couldn't find one on Ebay to show, but same
make made about 60 years ago. I also keep an AVO 8 but the batteries are
dead in that one. And yes, I *did* check it on the 1X range. YOU could
probably have made sense of the readings I was getting; they were
definitely lower on the damaged board in that region and *now* I know
why, but I'm no repair technician and never pretended to be so the
significance on me was a bit lost.
Are we clear now?
"** You are being very coy about what you REALLY did.
My post said to use an analogue ohm meter on the X1 range - nothing else
works near as well, especially any DMM I know of.
The ohms reading found corresponds to millivolts and volts across the
load - easily calibrated with a DVM and few resistors. I inked voltage
numbers on the ohms scale of my meter 45 years ago.
Most importantly, such meters deliver up to 50mA into the load, making
redundant any resistors that might be in parallel with device junctions.
Betcha you did nothing like that or else the near shorted C-E would have
jumped up and bit you. "
https://www.ebay.co.uk/itm/Selectest-Testmeter-Dlll-Old-Multi-
Meter/333272931128?hash=item4d989d5b38:g:jD8AAOSwxGBdNGvF
Not the same exact model as couldn't find one on Ebay to show, but same
make made about 60 years ago. I also keep an AVO 8 but the batteries are
dead in that one. And yes, I *did* check it on the 1X range. YOU could
probably have made sense of the readings I was getting; they were
definitely lower on the damaged board in that region and *now* I know
why, but I'm no repair technician and never pretended to be so the
significance on me was a bit lost.
Are we clear now?
Cursitor Doom
Oct 26, 2019, 11:55:41 AM10/26/19
to
On Sat, 26 Oct 2019 15:52:30 +0000, Cursitor Doom wrote:
> Not the same exact model as couldn't find one on Ebay to show, but same
> make made about 60 years ago.
Which is a lot more 'modern' than the one in the Ebay advert, plus mine
> Not the same exact model as couldn't find one on Ebay to show, but same
> make made about 60 years ago.
goes up to 2,500VDC.
Cursitor Doom
Oct 26, 2019, 4:56:10 PM10/26/19
to
On Sat, 26 Oct 2019 15:55:24 +0000, Cursitor Doom wrote:
> Which is a lot more 'modern' than the one in the Ebay advert, plus mine
> goes up to 2,500VDC.
Found it! Four hours of searching didn't go to waste after all.
> Which is a lot more 'modern' than the one in the Ebay advert, plus mine
> goes up to 2,500VDC.
http://www.richardsradios.co.uk/selectest.html
Not as old as I'd thought; 1972 vintage according to the advert.
Phil Allison
Oct 26, 2019, 6:52:07 PM10/26/19
to
Cursitor Doom wrote:
---------------------------
You did not post any.
Each junction should read about 10 to 20 ohms, on that meter.
B-C a bit lower than B-E, all the same for good devices that are the same.
FFS fess up and shame the Devil.
..... Phil
---------------------------
>
>
> "** You are being very coy about what you REALLY did.
>
> My post said to use an analogue ohm meter on the X1 range - nothing else
> works near as well, especially any DMM I know of.
>
> The ohms reading found corresponds to millivolts and volts across the
> load - easily calibrated with a DVM and few resistors. I inked voltage
> numbers on the ohms scale of my meter 45 years ago.
>
> Most importantly, such meters deliver up to 50mA into the load, making
> redundant any resistors that might be in parallel with device junctions.
>
> Betcha you did nothing like that or else the near shorted C-E would have
> jumped up and bit you. "
>
> Nope. I actually used one of these:
>
> https://www.ebay.co.uk/itm/Selectest-Testmeter-Dlll-Old-Multi-
> Meter/333272931128?hash=item4d989d5b38:g:jD8AAOSwxGBdNGvF
>
** So what happened to your ohm readings ??
>
> "** You are being very coy about what you REALLY did.
>
> My post said to use an analogue ohm meter on the X1 range - nothing else
> works near as well, especially any DMM I know of.
>
> The ohms reading found corresponds to millivolts and volts across the
> load - easily calibrated with a DVM and few resistors. I inked voltage
> numbers on the ohms scale of my meter 45 years ago.
>
> Most importantly, such meters deliver up to 50mA into the load, making
> redundant any resistors that might be in parallel with device junctions.
>
> Betcha you did nothing like that or else the near shorted C-E would have
> jumped up and bit you. "
>
> Nope. I actually used one of these:
>
> https://www.ebay.co.uk/itm/Selectest-Testmeter-Dlll-Old-Multi-
> Meter/333272931128?hash=item4d989d5b38:g:jD8AAOSwxGBdNGvF
>
You did not post any.
Each junction should read about 10 to 20 ohms, on that meter.
B-C a bit lower than B-E, all the same for good devices that are the same.
FFS fess up and shame the Devil.
..... Phil
Cursitor Doom
Oct 26, 2019, 8:31:20 PM10/26/19
to
** So what happened to your ohm readings ??
You did not post any.
Each junction should read about 10 to 20 ohms, on that meter.
B-C a bit lower than B-E, all the same for good devices that are the
same.
FFS fess up and shame the Devil.
There's no point now. I have checked all 6 of those transistors and found
one faulty one as described. The question in my mind now becomes, "can
that one transistor (Q9) being partly shorted cause the voltage readings
on the other transistors to be so far out of whack?" Now most people
would probably say "just stick a new transistor in there and see if it
works" but I'm going to Spice the voltage-to-current section just out of
curiosity. Since I'm not a repair tech and time is not a factor I can do
this.
I'm lucky to have an identical board, the Y-amplifier, which is identical
in every way except that it works so I've been able to get some useful
values from measuring it under power and getting meaningful and sane
voltage readings from it to compare to the faulty one's measurements
which are all over the place.
The simulation is almost ready to run but I have other things to do right
now so it'll have to wait until tomorrow.
Dave Platt
Oct 26, 2019, 9:53:29 PM10/26/19
to
In article <qp14d5$pv6$1...@dont-email.me>,
junction(s). Rather, it's acting as if something ohmic is _bypassing_
the junctions.
I wonder whether something inside the case (e.g. some form of
contamination, debris, etc.) has fallen onto the surface of the die
and is bridging the C and E wells (or the contacts or the bond wires).
Cursitor Doom <cu...@notformail.com> wrote:
>Well I don't do repair work for a living so defer to your wider knowledge
>of the subject. I just find it baffling how such a transistor can give
>readings like those I described, with a Rc-e lower than each of its Rc-b
>and Rb-e readings!
That sounds to me as if the fault isn't in the B/E or B/C
>Well I don't do repair work for a living so defer to your wider knowledge
>of the subject. I just find it baffling how such a transistor can give
>readings like those I described, with a Rc-e lower than each of its Rc-b
>and Rb-e readings!
junction(s). Rather, it's acting as if something ohmic is _bypassing_
the junctions.
I wonder whether something inside the case (e.g. some form of
contamination, debris, etc.) has fallen onto the surface of the die
and is bridging the C and E wells (or the contacts or the bond wires).
Phil Allison
Oct 26, 2019, 10:13:11 PM10/26/19
to
Dave Platt wrote:
------------------
>
> That sounds to me as if the fault isn't in the B/E or B/C
> junction(s). Rather, it's acting as if something ohmic is _bypassing_
> the junctions.
>
> I wonder whether something inside the case (e.g. some form of
> contamination, debris, etc.) has fallen onto the surface of the die
> and is bridging the C and E wells (or the contacts or the bond wires).
** Crikey - another one who has no clue about how transistors typically fail with second breakdown or gross leakage.
BJTs that merely hot for a long time often develop gross leakage and reduced C-E breakdown voltage.
Take any TO3 pak silicon power tranny, put it in an oven at 250C for ten minutes.
Then test it.
..... Phil
------------------
>
> That sounds to me as if the fault isn't in the B/E or B/C
> junction(s). Rather, it's acting as if something ohmic is _bypassing_
> the junctions.
>
> I wonder whether something inside the case (e.g. some form of
> contamination, debris, etc.) has fallen onto the surface of the die
> and is bridging the C and E wells (or the contacts or the bond wires).
BJTs that merely hot for a long time often develop gross leakage and reduced C-E breakdown voltage.
Take any TO3 pak silicon power tranny, put it in an oven at 250C for ten minutes.
Then test it.
..... Phil
Cursitor Doom
Oct 27, 2019, 6:06:22 AM10/27/19
to
On Sat, 26 Oct 2019 18:53:22 -0700, Dave Platt wrote:
> That sounds to me as if the fault isn't in the B/E or B/C junction(s).
> Rather, it's acting as if something ohmic is _bypassing_
> the junctions.
>
> I wonder whether something inside the case (e.g. some form of
> contamination, debris, etc.) has fallen onto the surface of the die and
> is bridging the C and E wells (or the contacts or the bond wires).
Phil Alison:
> That sounds to me as if the fault isn't in the B/E or B/C junction(s).
> Rather, it's acting as if something ohmic is _bypassing_
> the junctions.
>
> I wonder whether something inside the case (e.g. some form of
> contamination, debris, etc.) has fallen onto the surface of the die and
> is bridging the C and E wells (or the contacts or the bond wires).
"** Crikey - another one who has no clue about how transistors typically
fail with second breakdown or gross leakage.
BJTs that merely hot for a long time often develop gross leakage and
reduced C-E breakdown voltage.
Take any TO3 pak silicon power tranny, put it in an oven at 250C for ten
minutes.
Then test it. "
example of a test is a little on the extreme side to say the least.
Whilst secondary breakdown *can* happen with small signal devices, it's
much less common. I suspect your outlook is coloured by years of seeing
burned out TO-3s in audio amps, but it's nothing like as prevalent with
SSTs so let's give the guy a break, eh?
Phil Allison
Oct 27, 2019, 7:25:55 AM10/27/19
to
Cursitor Doom wrote:
--------------------
>
> Phil Alison:
>
>
> "** Crikey - another one who has no clue about how transistors typically
> fail with second breakdown or gross leakage.
>
> BJTs that merely hot for a long time often develop gross leakage and
> reduced C-E breakdown voltage.
>
> Take any TO3 pak silicon power tranny, put it in an oven at 250C for ten
> minutes.
>
> Then test it. "
>
> Yes, but we're talking about a small signal transistor here and your
> example of a test is a little on the extreme side to say the least.
>
** You have never revealed the transistor's number.
The OP describes it as being a "TO8 in a tin can" which makes no sense.
A CRO sweep amplifier is not a small signal circuit, it is large signal.
Maybe you meant a TO5 round metal pak like this ?
http://oldtube.com/2N5321-Fairchild(Philips-made)-DC335-1pc.jpg
Rated at 75V, 2A, 50MHz and 10 watts
The case would glow in the dark at 10 watts.
FYI:
I've seen hundreds like the above with shorted C-E - due to over current, over voltage or over temp.
Ones with low C-E resistance got lucky and were just cooked a bit.
Doped silicon is wacky stuff.
Few texts describe all or even any the failure modes.
..... Phil
--------------------
>
> Phil Alison:
>
>
> "** Crikey - another one who has no clue about how transistors typically
> fail with second breakdown or gross leakage.
>
> BJTs that merely hot for a long time often develop gross leakage and
> reduced C-E breakdown voltage.
>
> Take any TO3 pak silicon power tranny, put it in an oven at 250C for ten
> minutes.
>
> Then test it. "
>
> Yes, but we're talking about a small signal transistor here and your
> example of a test is a little on the extreme side to say the least.
>
The OP describes it as being a "TO8 in a tin can" which makes no sense.
A CRO sweep amplifier is not a small signal circuit, it is large signal.
Maybe you meant a TO5 round metal pak like this ?
http://oldtube.com/2N5321-Fairchild(Philips-made)-DC335-1pc.jpg
Rated at 75V, 2A, 50MHz and 10 watts
The case would glow in the dark at 10 watts.
FYI:
I've seen hundreds like the above with shorted C-E - due to over current, over voltage or over temp.
Ones with low C-E resistance got lucky and were just cooked a bit.
Doped silicon is wacky stuff.
Few texts describe all or even any the failure modes.
..... Phil
Cursitor Doom
Oct 27, 2019, 8:07:37 AM10/27/19
to
On Sun, 27 Oct 2019 10:06:19 +0000, Cursitor Doom wrote:
** You have never revealed the transistor's number.
The OP describes it as being a "TO8 in a tin can" which makes no sense.
A CRO sweep amplifier is not a small signal circuit, it is large signal.
Maybe you meant a TO5 round metal pak like this ?
http://oldtube.com/2N5321-Fairchild(Philips-made)-DC335-1pc.jpg
Rated at 75V, 2A, 50MHz and 10 watts
The case would glow in the dark at 10 watts.
Probably. Did I write TO-8? I meant to type TO-18. It's a 2N3251 and in
** You have never revealed the transistor's number.
The OP describes it as being a "TO8 in a tin can" which makes no sense.
A CRO sweep amplifier is not a small signal circuit, it is large signal.
Maybe you meant a TO5 round metal pak like this ?
http://oldtube.com/2N5321-Fairchild(Philips-made)-DC335-1pc.jpg
Rated at 75V, 2A, 50MHz and 10 watts
The case would glow in the dark at 10 watts.
this circuit it's working well within its V&A ratings, as one would
expect with a design by Hewlett-Packard.
Phil Allison
Oct 27, 2019, 8:16:26 AM10/27/19
to
Cursitor Doom wrote:
---------------------
>
> ** You have never revealed the transistor's number.
>
> The OP describes it as being a "TO8 in a tin can" which makes no sense.
>
> A CRO sweep amplifier is not a small signal circuit, it is large signal.
>
> Maybe you meant a TO5 round metal pak like this ?
>
> http://oldtube.com/2N5321-Fairchild(Philips-made)-DC335-1pc.jpg
>
> Rated at 75V, 2A, 50MHz and 10 watts
>
> The case would glow in the dark at 10 watts.
>
> Probably. Did I write TO-8? I meant to type TO-18. It's a 2N3251 and in
> this circuit it's working well within its V&A ratings, as one would
> expect with a design by Hewlett-Packard.
>
** Pathetic.
The max ratings of any BJT on a BJC can be massively exceeded by the simplest of accidents while servicing or even cleaning.
Dropping a toll or screw will do it.
FFS get real.
.... Phil
---------------------
>
> ** You have never revealed the transistor's number.
>
> The OP describes it as being a "TO8 in a tin can" which makes no sense.
>
> A CRO sweep amplifier is not a small signal circuit, it is large signal.
>
> Maybe you meant a TO5 round metal pak like this ?
>
> http://oldtube.com/2N5321-Fairchild(Philips-made)-DC335-1pc.jpg
>
> Rated at 75V, 2A, 50MHz and 10 watts
>
> The case would glow in the dark at 10 watts.
>
> Probably. Did I write TO-8? I meant to type TO-18. It's a 2N3251 and in
> this circuit it's working well within its V&A ratings, as one would
> expect with a design by Hewlett-Packard.
>
The max ratings of any BJT on a BJC can be massively exceeded by the simplest of accidents while servicing or even cleaning.
Dropping a toll or screw will do it.
FFS get real.
.... Phil
Cursitor Doom
Oct 27, 2019, 10:00:11 AM10/27/19
to
** Pathetic.
The max ratings of any BJT on a BJC can be massively exceeded by the
simplest of accidents while servicing or even cleaning.
Dropping a toll or screw will do it.
FFS get real.
sealed casing. THE FAULT AROSE *BEFORE* THE CASE WAS EVEN REMOVED.
<composing myself>
Anyway, I can see your old attitude problem resurfacing and you reverting
to being your usual snarky bastard self so this thread is over AFAIC. I
will not be looking for any more replies from you via GG as you're not
adding anything of value any more.
Have a nice life and enjoy the Rugby World Cup Final Hahaha! >:-}
Phil Allison
Oct 27, 2019, 4:48:43 PM10/27/19
to
Cursitor Doom is an IDIOT wrote:
-----------------------------------
The scope is decades old, anything could have happened in the past.
Metal case transistors are highly vulnerable cos the collector is exposed.
> <composing myself>
** Good idea - cos you are raving like a lunatic.
> Anyway, I can see your old attitude problem
** Listen you ASD fucked moron -
YOU have the bad attitude.
Big time.
..... Phil
-----------------------------------
>
> ** Pathetic.
>
> The max ratings of any BJT on a BJC can be massively exceeded by the
> simplest of accidents while servicing or even cleaning.
>
> Dropping a toll or screw will do it.
>
> FFS get real.
>
> I can't see HTH that's going to happen just out of the blue inside the
> sealed casing. THE FAULT AROSE *BEFORE* THE CASE WAS EVEN REMOVED.
>
** Insane.
> ** Pathetic.
>
> The max ratings of any BJT on a BJC can be massively exceeded by the
> simplest of accidents while servicing or even cleaning.
>
> Dropping a toll or screw will do it.
>
> FFS get real.
>
> I can't see HTH that's going to happen just out of the blue inside the
> sealed casing. THE FAULT AROSE *BEFORE* THE CASE WAS EVEN REMOVED.
>
The scope is decades old, anything could have happened in the past.
Metal case transistors are highly vulnerable cos the collector is exposed.
> <composing myself>
** Good idea - cos you are raving like a lunatic.
> Anyway, I can see your old attitude problem
YOU have the bad attitude.
Big time.
..... Phil
John-Del
Oct 28, 2019, 6:03:09 PM10/28/19
to
On Sunday, October 27, 2019 at 4:48:43 PM UTC-4, Mr. Charm and Warmth wrote:
>
> ** Listen you ASD fucked moron -
>
> YOU have the bad attitude.
>
> Big time.
>
>
> ..... Phil
Phil, you've been run out of every group you to which you've ever belonged anywhere in the civilized world.
>
> ** Listen you ASD fucked moron -
>
> YOU have the bad attitude.
>
> Big time.
>
>
> ..... Phil
Yet it never occurs to you that the problem might be *you*...
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