Date   
Diagnosing faulty Transistors with a Curve Tracer

 
Edited

This is an issue which has been cooking in my thoughts for a while.

On older discrete power amplifiers, which have suffered failure, the main power transistors test OK on all usual devices, when out-of-circuit. But when in-circuit, the amplifier fails, and replacement of those transistors solves the problem.

So normal testing is NOT able to identify the failed transistor.

Why does this bother me, if all I need to do is throw in a new transistor?

Because the overall majority of these transistors are now NLA, and the widely advertised replacements are almost guaranteed to be counterfeits.
So if there is a way to positively identify one failed transistor, then I do not need to replace all 4 of them, with dubious units.

Any ideas?

Menahem Yachad
CondorAudio

Re: 453 calibrator

 

On Wed, May 9, 2018 at 01:15 pm, Richard Knoppow wrote:


On my schematic BA and BB are shown right on the edge line of the board. They
look like they are connected together but are not.
You nailed it. you beat me to it. I did attribute it to a mistake but it is not. I am too aware of mistakes on prints, thy occur quite a bit in consumer. You see a wire that says 12 volts and then a inch or two away it says 0 volts. And it is no mistake like the one voltage is something else, I have seen them where it is simply not possible. And they don't really care.

Anyone who doesn't see it - observe the dot that indicates a connection there at BA and BB. Look at the other dots. This one is bigger. Well it is bigger because it is not a dot, it is a circle. The coax is grounded on that side but not on the other. This is not that uncommon.

I have to admit it fooled me up until very recently. I have shit eyesight, I thought I was used to it and I am to a point, but still I missed this.

That doesn't change the fact that I dismissed it as a mistake for troubleshooting purposes up to this point, and the resistors were the wrong value.

This is nothing. Poor eyesight contributed to me frying a 7603. I switched two of the plugs on the Z board and dumped 130 volts into the unobtanium horizontal IC. Luckily I had a parts donor handy. If not I would have been guilty of criminal involuntary scopicide. So this is nothing.

Re: 7T11 sampling timebase - how does it behave?

 

IIRC, the 7T11 has a Random Sampling mode; the dots on screen are not sequential.
Instead, the sampling window is intentionally jittered horizontally.
This allows you to see the trigger point without the need for a delay line, which would reduce the bandwidth.
Keep an eye out for a Tek Concepts book on sampling scopes.

HankC, Boston, WA1HOS

Re: 7T11 sampling timebase - how does it behave?

 

Dennis,

As an extensive user of the 7S11/7T11 (I own 6 7S11s 4 7T11s, and 2 7T11As) they are awful to use
I don't fully agree with you on this, Dennis. Whereas the 7S14 behaves almost exactly like an analog 'scope, as you describe, the 7S11/7T11 behaves very differently. Although it (actually, mostly the 7T11) does remain a bit finicky to use, the most important thing I guess before using the 7S11/7T11 is realising it's not a general purpose 'scope setup, taking a deep breath and letting go of the assumption that the time settings are some sort of equivalent to normal time base setting (s/div.) with an ordinary time-expanded window in it, like with a second (delayed) time base. I do agree that triggering effort, noise level etc. do remain less pleasant than when using a 7S14 or a 7104 equipped as you mention. OTOH, no amount of effort will show an 8 GHz waveform on the 7S14 or 7104 - or a 50 ps step with any fidelity. I get quite good results with a 7S11/S-4/7T11A in a 7854, using digital storage and filtering, though I haven't exactly tried things like your 10 ps/div or 2 mV/div. I might give that a try though, one of these days with the 7854.
Not only have I had fun playing with the 7S11/7T11 but I have had results as well; one does get used to them. As an example, I certainly prefer adjusting the fast edge of a PG-506 using a 7S11/7T11 over a 7104 or 7S14... Signal fidelity (shape and speed) cannot be matched by either of the two latter setups. And I cannot judge the performance of my home-made TD-pulser without the 7S11/S-4/7T11 setup.

Raymond

Re: 453 calibrator

Phillip Potter
 

Geeze... I am such a crazy guy... don't worry about the rar download link, lop pol.  The link is a scan of my manual, in color and 20000 and up.  Just what I needed.  Sorry for the silly confusion.

Phil

On 5/9/2018 3:58 PM, Phillip Potter wrote:
would appreciate that download or a link...

Re: 453 calibrator

Phillip Potter
 

I have a 20000+ 453 and would appreciate that download or a link...

Thanks,

Phil

On 5/9/2018 11:49 AM, lop pol via Groups.Io wrote:
BTW if anyone needs the 453 above SN 20,000 manual I can send it to you. I can't remember where I got it. It was a 6 part .rar download.

Re: 7T11 sampling timebase - how does it behave?

 

On Wed, May 9, 2018 at 02:47 pm, Dave Wise wrote:


I question one point, Raymond. The 7S14's delay line delays the signal long
enough for the rising edge to hit the sampling gate - not the CRT - after the
trigger. That's what you meant, right?
Yes, Dave, that is sort of what I meant. In my description, I meant to indicate the ultimate goal, which is to show the vertical signal on the crt long enough after the triggering event but maybe I didn't make things as clear as I should have. The delay line has to be positioned *before* the sampling gate i.e. in the analog part, because after the sampling gate the signal isn't an *analog* representation of the input signal anymore nor even a sequence of points of the same edge but a sequence of sampled points on (usually) subsequent edges. So, the analog signal is delayed by the delay lines (one for each channel, DL1 and DL2 in the Service Manual) before being "chopped into pieces". In the SM you can see the "trigger pickoff" (CH1 only) right after the compensation circuits. These serve to compensate for the adverse phase and amplitude effects of the delay line on the signal - and on the input impedance. The trigger signal is output to the horizontal (ramp) circuits on J50.

Raymond

Re: 7T11 sampling timebase - how does it behave?

 

Regarding the differences between the 7S14 and the 7S11/7T11:

As near as I can tell from using the 7S14 extensively, anyone familiar with any very common dual trace dual timebase Tek product would instantly be familiar with how to use the 7S14. It was extremely easy to use and it worked exactly as it appeared to suggest from looking at it. I looked forward to using 7S14s every opportunity I could before I got a 7104/7A29/7B10/7B15.

As an extensive user of the 7S11/7T11 (I own 6 7S11s 4 7T11s, and 2 7T11As) they are awful to use, they take at least a half hour to get working together, and you often have to confirm a setup first on a 7A29/7B10 to be sure you eliminate anything that can possibly be causing the sampling plugins to not work in spite of you doing everything right. Finally, the amplitude noise of the S4 (I have 3 of them) is more than 2mV and the time jitter of the 7T11s is so great that you can't use them on the most sensitive vertical setting or on the fastest two horizontal settings. These two plugins are a nightmare to use.

I don't believe you can get a clean trace at 2mV/Div and 10pSec/Div or even 20pSec/Div using these plugins. I would love to be proved wrong. If you have proof send me a photograph (@Dennis_Tillman_W7pF) and tell me how you did it. I would love to know how to do it.

Dennis Tillman W7PF

-----Original Message-----
Roger Evans Sent: Wednesday, May 09, 2018 12:08 PM

Chris, Dennis,
I wondered why the 7S14 had the delayed timebase and Vernier control of the
delta-delay markers but this was omitted on the 7T11. There could be
several possible reasons and Dennis may be able to point to the truth.

The 7S14 has a delay line so that you can see the trigger point and make
accurate time measurements from the trigger to other features on the
waveform. On the 7T11 in sequential scan you are looking 10s of nsec after
the trigger so you largely lose any time reference from the trigger event.

Another very good reason might be that the 7T11 is already very well filled
with multiple boards.

Roger


--
Dennis Tillman W7PF
TekScopes Moderator

Re: 7T11 sampling timebase - how does it behave?

Dave Wise
 

I question one point, Raymond. The 7S14's delay line delays the signal long enough for the rising edge to hit the sampling gate - not the CRT - after the trigger. That's what you meant, right?

Dave Wise
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Raymond Domp Frank <@Raymond>
Sent: Wednesday, May 09, 2018 2:29 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 7T11 sampling timebase - how does it behave?

On Wed, May 9, 2018 at 12:07 pm, Roger Evans wrote:


The 7S14 has a delay line so that you can see the trigger point and make
accurate time measurements from the trigger to other features on the waveform.
On the 7T11 in sequential scan you are looking 10s of nsec after the trigger
so you largely lose any time reference from the trigger event.
The 7S14 is specified to "only" 1 GHz. It's very much easier to make a low-distortion (amplitude, phase) delay line for frequencies up to 1 GHz than up to say 11 or 14 GHz, which is where the 7T11 is often used.
The delay line affects the signal in the vertical stage (that would have to be e.g. the 7S11), not in the time base (7T11), so available space in the 7T11 would not be a factor.
It's not in fact the delay line that is used for making accurate time measurements like the 7S14 can; it's the accuracy of the delayed-time-base circuits that do, by showing(/measuring) the delay from one event to another. The 7S14 has a fixed delay time for the signal in the vertical circuits to make it arrive on the plates long enough after the trace starts to make it visible, like in a normal analog 'scope with vertical delay line. The 7T11 in sequential trigger mode has its special way of delaying the display of the vertical signal: It shows parts of many trigger events that happen at least one period (or triggering edge) after the actual events (one event per dot). The setting applies the same (>1 period) delay for each dot.

Raymond

Re: 7T11 sampling timebase - how does it behave?

 

On Wed, May 9, 2018 at 12:07 pm, Roger Evans wrote:


The 7S14 has a delay line so that you can see the trigger point and make
accurate time measurements from the trigger to other features on the waveform.
On the 7T11 in sequential scan you are looking 10s of nsec after the trigger
so you largely lose any time reference from the trigger event.
The 7S14 is specified to "only" 1 GHz. It's very much easier to make a low-distortion (amplitude, phase) delay line for frequencies up to 1 GHz than up to say 11 or 14 GHz, which is where the 7T11 is often used.
The delay line affects the signal in the vertical stage (that would have to be e.g. the 7S11), not in the time base (7T11), so available space in the 7T11 would not be a factor.
It's not in fact the delay line that is used for making accurate time measurements like the 7S14 can; it's the accuracy of the delayed-time-base circuits that do, by showing(/measuring) the delay from one event to another. The 7S14 has a fixed delay time for the signal in the vertical circuits to make it arrive on the plates long enough after the trace starts to make it visible, like in a normal analog 'scope with vertical delay line. The 7T11 in sequential trigger mode has its special way of delaying the display of the vertical signal: It shows parts of many trigger events that happen at least one period (or triggering edge) after the actual events (one event per dot). The setting applies the same (>1 period) delay for each dot.

Raymond

Re: 453 calibrator

Richard Knoppow
 

On my schematic BA and BB are shown right on the edge line of the board. They look like they are connected together but are not. BB goes to ground and to the shield of the coax that goes from R1274 to R1275. BA goes to the center conductor of this coax from R1274. The ground at BB grounds one end of the shield. Its probably grounded that way to prevent a ground loop. No current can flow through the shield. The output from the collector of Q1274 goes through some resistors and the coax to more resistors, through the test loop and to ground. Different circuit than is grounded at BB. The BNC connector is fed from a dropping resistor in the line from Q1274. It is not grounded at the BNC, however, the shield of the BNC goes to ground. Again, this ground is separate from both the coax shield and the loop ground.
The whole line from the collector of Q1274 should show some voltage and some resistance to ground up to the test loop, which will measure ground (or a very low resistance at the R1278-R1277 end. The center conductor of the BNC should read about 200 ohms with the calibrate voltage switch in the 1.0 V position and about 20 ohms in the 0.1 V position. Again, the coax feeding the BNC is grounded at one end only.
If you are measuring a short to ground at the emitter of Q1274 I would be suspicious of C1251. I think that would also pull down the +12V line or pop the 4.7 ohm resistor at R1251.
The PDF I have is from BAMA and is numbered 070-00478-00
I am not editing this so as to allow some context.

On 5/9/2018 12:24 PM, Mike Merigliano wrote:
Why would either BA or BB be a dead short (at ground) to Q1274's emitter? There is a 2.19K resister between the emitter and either BB or BA.  I guess what I'm missing is how someone could see a short on the schematic, even if they mis-interpreted the line representing the board's boundary as a wire or trace. I am not an expert, so when someone sees something on a schematic that I don't, I want to know why.
Connection BB is probably not needed when everything else is connected anyway, as there are two other ground returns -- the one for the 1 volt BNC output looks redundant to BB, and another 180 ohms kicks-in for 0.1 output. The other involves the current-test loop, and there is another 220 ohms involved.
On 5/9/2018 12:29 PM, Chuck Harris wrote:
No, you aren't missing anything.  What Jeff was saying
is if BA is truly at ground, then you cannot have a signal
out your calibrator.  It may appear to be grounded if you
use an ohmmeter that is on too high a scale... due to the
160, or so ohms that the circuit inherently has to ground.

-Chuck Harris

Mike Merigliano wrote:
The signal is not shorted to ground -- it goes through a 2.19K resistor in series
first, so there is no short. My Tek 453 has a calibrator signal, at specification. My
ohmeter and voltmeter check measurements between/around Q1274, point BA, R1274, and
point BB  match what is on the schematic.

Maybe I am missing something.

--
Richard Knoppow
dickburk@...
WB6KBL

Re: 453 calibrator

toby@...
 

On 2018-05-09 2:49 PM, lop pol via Groups.Io wrote:
BTW if anyone needs the 453 above SN 20,000 manual I can send it to you. I can't remember where I got it. It was a 6 part .rar download.
Has also been recently scanned here:

http://chiclassiccomp.org/docs/index.php?dir=%2Ftesteq/Tektronix



Re: 453 calibrator

Chuck Harris
 

People misinterpret things all of the time.

And people use their test equipment wrongly quite a lot.
I am not saying that is happening here, but it feels like
it might be.

If BA is truly at ground, then his scope is wired incorrectly.

Maybe someone measured BA to ground, found it wasn't, then
misinterpreting the schematic, added a jumper between BA and BB.

Maybe the coax has been subject to the soldering iron too many
times, and the center insulation is now shorted to the ground
braid.

The only reason BB is at ground is to ground the shield on the
coax. Purely a noise reduction issue.

-Chuck Harris

Mike Merigliano wrote:

Why would either BA or BB be a dead short (at ground) to Q1274's emitter? There is a
2.19K resister between the emitter and either BB or BA. I guess what I'm missing is
how someone could see a short on the schematic, even if they mis-interpreted the line
representing the board's boundary as a wire or trace. I am not an expert, so when
someone sees something on a schematic that I don't, I want to know why.

Connection BB is probably not needed when everything else is connected anyway, as
there are two other ground returns -- the one for the 1 volt BNC output looks
redundant to BB, and another 180 ohms kicks-in for 0.1 output. The other involves the
current-test loop, and there is another 220 ohms involved.

Re: 453 calibrator

Mike Merigliano
 

Why would either BA or BB be a dead short (at ground) to Q1274's emitter? There is a 2.19K resister between the emitter and either BB or BA.  I guess what I'm missing is how someone could see a short on the schematic, even if they mis-interpreted the line representing the board's boundary as a wire or trace. I am not an expert, so when someone sees something on a schematic that I don't, I want to know why.

Connection BB is probably not needed when everything else is connected anyway, as there are two other ground returns -- the one for the 1 volt BNC output looks redundant to BB, and another 180 ohms kicks-in for 0.1 output. The other involves the current-test loop, and there is another 220 ohms involved.

On 5/9/2018 12:29 PM, Chuck Harris wrote:
No, you aren't missing anything. What Jeff was saying
is if BA is truly at ground, then you cannot have a signal
out your calibrator. It may appear to be grounded if you
use an ohmmeter that is on too high a scale... due to the
160, or so ohms that the circuit inherently has to ground.

-Chuck Harris

Mike Merigliano wrote:
The signal is not shorted to ground -- it goes through a 2.19K resistor in series
first, so there is no short. My Tek 453 has a calibrator signal, at specification. My
ohmeter and voltmeter check measurements between/around Q1274, point BA, R1274, and
point BB match what is on the schematic.

Maybe I am missing something.

Re: 7T11 sampling timebase - how does it behave?

Roger Evans
 

Chris, Dennis,
I wondered why the 7S14 had the delayed timebase and Vernier control of the delta-delay markers but this was omitted on the 7T11. There could be several possible reasons and Dennis may be able to point to the truth.

The 7S14 has a delay line so that you can see the trigger point and make accurate time measurements from the trigger to other features on the waveform. On the 7T11 in sequential scan you are looking 10s of nsec after the trigger so you largely lose any time reference from the trigger event.

Another very good reason might be that the 7T11 is already very well filled with multiple boards.

Roger

Re: 453 calibrator

Brendan
 

BTW if anyone needs the 453 above SN 20,000 manual I can send it to you. I can't remember where I got it. It was a 6 part .rar download.

Re: 453 calibrator

Chuck Harris
 

No, you aren't missing anything. What Jeff was saying
is if BA is truly at ground, then you cannot have a signal
out your calibrator. It may appear to be grounded if you
use an ohmmeter that is on too high a scale... due to the
160, or so ohms that the circuit inherently has to ground.

-Chuck Harris

Mike Merigliano wrote:

The signal is not shorted to ground -- it goes through a 2.19K resistor in series
first, so there is no short. My Tek 453 has a calibrator signal, at specification. My
ohmeter and voltmeter check measurements between/around Q1274, point BA, R1274, and
point BB match what is on the schematic.

Maybe I am missing something.

On 5/9/2018 10:19 AM, Jeff Urban wrote:
On Wed, May 9, 2018 at 08:13 am, Mike Merigliano wrote:

There is no error here; BB is a ground point, and the emitter of Q1274 goes to
it via R1274 in series.
Then there can be no output at the calibrator terminal unless the whole thing
floats and has a separately isolated power supply. The signal would forever be
shorted to ground.

Re: 453 calibrator

Mike Merigliano
 

The signal is not shorted to ground -- it goes through a 2.19K resistor in series first, so there is no short. My Tek 453 has a calibrator signal, at specification. My ohmeter and voltmeter check measurements between/around Q1274, point BA, R1274, and point BB  match what is on the schematic.

Maybe I am missing something.

On 5/9/2018 10:19 AM, Jeff Urban wrote:
On Wed, May 9, 2018 at 08:13 am, Mike Merigliano wrote:

There is no error here; BB is a ground point, and the emitter of Q1274 goes to
it via R1274 in series.
Then there can be no output at the calibrator terminal unless the whole thing floats and has a separately isolated power supply. The signal would forever be shorted to ground.



Re: Way OT, but maybe interesting: Li-ion battery observations and questions

stefan_trethan
 

They make plenty of mistakes too.
Maybe worst was the DHR243 hammer (XRH01 in the US).
I could tell something wasn't right just by turning the chuck by hand,
it sounded awful as if something was binding. After some tinkering I
noticed the problem went away if I loosened the gearbox screws ever so
slightly. Power draw from the battery with the drill turning idle also
dropped to about half. They just mashed the gears together way too
tight, causing the binding. Some shims fixed that but this it not OK
for a premium product, clearly a design error not accounting for the
length tolerance of an injection molded plastic housing.

The grips are way too skinny even for small hands and the rubber
overmolding is very rough. On some of the tools there is sharp
injection molding flash right underneath the trigger button, where you
feel it every time you pick the thing up. Generally the fit of the
housings is poor, the Bosch tools fit together so well you barely
notice any seam but the Makita tools all have huge gap designed in so
the mismatch isn't so obvious. The Bosch tools feel nice and smooth in
the hand, you want to hold them. Not so with Makita, you almost want
to wear gloves so the rubber off-road-tire tread doesn't hurt your
hand.

There are too many safety catches on some of the tools. I only have
two hands and accordingly reduced the number of safety catches to
match the number of hands. I consider it sufficient if both hands are
required to activate a tool, I don't need a safety button for each
foot and the tongue too.

Don't get me wrong, I know this is criticism at a somewhat elevated
level. But these are expensive premium tools and I had to take most of
them apart immediately to fix them in some way (including the
chainsaw).

If it wasn't for the one thing - the battery platform, I would have
sent the first items back and switched to Bosch while I still could
(no hope now). Bosch just pissed me off with making the batteries for
their power tool and garden tool range intentionally incompatible,
just to spite me.

ST

On Wed, May 9, 2018 at 6:11 PM, Pete Lancashire <xyzzypdx@...> wrote:
I know this thread is getting pretty long here but I'll also toss in my
vote for Makita. They're one of the few independent companies that still
make design and manufacture their own tools and the one time I had problems
with a model that had a brushless motor Makita of America sent me a
replacement with an RMA tag and told me to return the defective one one at
my leisure.

Re: 453 calibrator

 

On Wed, May 9, 2018 at 08:13 am, Mike Merigliano wrote:


There is no error here; BB is a ground point, and the emitter of Q1274 goes to
it via R1274 in series.
Then there can be no output at the calibrator terminal unless the whole thing floats and has a separately isolated power supply. The signal would forever be shorted to ground.