Odd Transistor Readings

[Cursitor Doom]

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.

http://www.richardsradios.co.uk/selectest.html

Not as old as I'd thought; 1972 vintage according to the advert.



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[Phil Allison]

Cursitor Doom wrote:

---------------------------

"** 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 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]

** 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.



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[Dave Platt]

In article <qp14d5$pv6$1@dont-email.me>,
Cursitor Doom <curd@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
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]

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

 

[Cursitor Doom]

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:


"** 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.
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?



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[Phil Allison]

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

 

[Cursitor Doom]

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
this circuit it's working well within its V&A ratings, as one would
expect with a design by Hewlett-Packard.





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[Phil Allison]

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

 

[Cursitor Doom]

** 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.

<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! >:-}



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[Phil Allison]

Cursitor Doom is an IDIOT wrote:

-----------------------------------

** 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.

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

 

[John-Del]

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.

Yet it never occurs to you that the problem might be *you*...