DCinDC - DIY Component Tester using an Oscope

This device tests components IN CIRCUIT, un-powered.

No desoldering.

Put your probes on the DUT (device under test) and look at the waveform. Compare to the other channel's similar component. DONE.

Waveforms will differ, but comparison to the other channel in stereo gear will usually lead you to where you need to be. . . .

So if I test two transistors at the same spot in each channel, and the curves differ, one of the two is bad, but I still need to figure out which one? Correct?
 
I'm pretty sure you had a good idea which channel was bad before you started troubleshooting it.
 
I find that a "good" transister has a "typical" diode curve across a pair of legs. A bad transister reads shorted or open.

Supporting curcuit can make the curve look a bit wonky but if side to side is about the same weird, that's not the droid you're looking for.

It's a simple easy quick tool to hunt bad parts. You may get circuit interference that makes the test fail but removing a few like that for out if circuit testing is easier that trying to find bad places chasing voltage readings on a live circuit. Failed parts in a live circuit can throw the vales off all over the place. A bad ground can screw up the voltages in the whole circuit.

It's not a magic tool, just another great tool to locate bad parts.
 
Well, that may have been my dumbest post ever. :rolleyes:

The only thing that sort of NOT makes it dumb is that it's hard to tell what channel is what on many items.

Side to side comparison IS a good trouble shooting technique!
 
The only thing that sort of NOT makes it dumb is that it's hard to tell what channel is what on many items.

Side to side comparison IS a good trouble shooting technique!

Yeah, that must be it. I was distracted by a baseball game and a few beers when I wrote that. That's my story and I'm sticking to it.

This is timely, since I currently have a receiver with one channel working perfectly and one that is flaky. I think I'll throw one of these together.
 
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Being semi-facetious here (both as a rebuke to the octopus.pdf file and as a thought experiment that would teach people how to use the tool), feed a capacitor versus an inductor (that doesn't saturate at the frequencies and currents presented by the test equipment) to a curve tracer... what's the difference on the oscilloscope display? :D
 
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