how to troubleshoot?

[Dave Krooshof]

>So, how do I test for faulty op amps, capacitors,
>transistors with my little DMM?  the tip on the transistors being two diodes
>in a three legged race is a good start for me!

Let's make a Checklist for amptesting. As a oscillator is an amp that
feedbacks through a filter, in a way, so let's stick with the amp for
reasons of clarity.
Say we have a broken Amp, we'll call it Harry for the time being.

So Harry is broken. Pity. What shall we test first?

1. Fuse. No need to open the box yet.
asuming that's OK,
2. voltage of the powersupply. We'll need + and - mostly. (*)
If that's alive,
3. any signal true the pre amp? Check the headphones.
Let's say the we narrowed the problem down to the power amp.
Now. How can we tell which transistors are alive, and which are not, while
leaving them in the print?

What I do, mostly, is testing if there is a bias voltage on every transistor.

Doing the diode-behavoir-check gets corrupted due to other components in
the circuit. It does give some idea though.



One personal question: I have one amp, identical to another. They both
behave normally, in every way I can tell. But one of them kicks out the
secondairy fuses out (it has both primairy and secondairy fuses as in
before and after the powersupply)
after some time of use. Or quite fast, mostly. What can I check?

The problem with me is that I do know the mediumlevel electronics, but I
crash on the just-above-basics, mostly.


Dave


* (I'm into the word 'mostly', mostly due to South Park, where Eric Cartman
whatched Aliens, mostly. So actually I should spell mhöhstly.)

--------------------------------------------
Dave Krooshof http://www.xs4all.nl/~krooshof
geluidstechnicus @ http://www.ahk.nl/the/theatertechniek_ov.html
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