Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old June 1st 16, 05:00 PM posted to sci.electronics.repair
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Default Scopes, Horizontal Deflection

In article ,
says...

Thanks. I actually just checked it real quick with the scope but did not pay alot of attention to the DC levels. I actually don't even know the pinout yet.

But I got square waves on one pin the the on/off time varies with the ten turn pot on the front panel for delay. That puts the problem right there, I should be able to smell it.

If the circuit works they way I think, which is they are feeding the emitter of Q4565, I do not like that. I mean I think it is bad because of the readings, but I think it went bad because of the way they used it.

But really, they probably had no other choice. I have seen it before, I have done failure mode analysis. And I have found that at times, they simply had no other choice and their circuit was going to beat on this certain part.

So anyway, what to put in there. I am not going to pay eBay $37 for a 11132-0002-1005 transistor, even if it is in original packaging. (I made the number up so don't bother)

It is pretty much a common base amp, but not really used linear, I THINK. No, I am pretty sure. You see the base hard biased by the two 1K resistors making the base voltage -4 volts. And it says right there that -3 volts starts B sweep.


They sometimes do that to isolate the voltage levels on the collector
side and keep the switching polarity the same.

Its a faster switching method if you have a HV side verses low voltage
side rather then adding a inverter stage.

CaseCode config..

I am only going by your description..

Jamie


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Old June 2nd 16, 11:56 AM posted to sci.electronics.repair
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Default Scopes, Horizontal Deflection

Good that you recognize that as cascode. I've ran into techs all over the place who have no clue what that is and think you are making a mistake and mean cascade. (as of now I can tell you my spellcheck does not now WTF cascode is)

Anyway I had to pull the Tek off the bench for a bit to do a Luxman R-117. Healthy receiver really. Thought maybe it was BFC but it's 160 a channel and built for it. But I am back on it next time I go down there.

But anyway, that is pretty much the word - cascode. Used to get the maximum voltage gain.

Usually it has a very high output impedance but they way they got it the transistor is just pulsed I think. It is like Q 4565 is used as a comparator. It would have to be because it appears to feed the R/C network created by the time/div switch.

The more I work on Teks, the more I am impressed with their designing skill.. I have never seen anything like it, it is almost scary. Like now, I am going to look into whatever specs I can get on Q 4565 before I just stick something in there.

I got a 561A that was built before I was born and the technology in it is amazing. I got the good plugins for it too, dual time base and dual trace. And almost all tube. In fact I think it may predate tunnel diode triggering. I mean, it may predate tunnel diodes :-)

And mine has a very strong CRT with no screen burn at all.

Anyhow, I think the main thing I need in this transistor is high gain. Voltage and current requirements are minimal. Frequency response should not be much of a problem these days. Since all it does is pulse, even if the ft of the replacement is up in the gigahertz there should be no problem.

I'll keep y'all posted.

And thanks.
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