On Monday 25 November 2002 04:06, Jeffrey Madore wrote:
> Vic,
>
> I recently had problems working on a solid state final. The transistors
> idled fine but the minute I applied drive the collector current went way up
> and the output was low. I too, let the smoke out of some expensive
> transistors.
>
> What I found, through careful inspection, was a bad chip capacitor in the
> collector circuit. This final was also subjected to a mismatched load
> which, I believe, caused the cap to fail.
>
> It had me scratching my head though, as I knew where the problem was but
> couldn't see the problem until I started pocking around with a bright
> light, magnifying glass, and a dental tool.
Sounds like the sort of thing that might easily cause Vic's problem. Another
area to check is any r/l/c feedback round the transistors, and also the
supply decoupling. Faults in either could cause destructive oscillation under
drive.
A goos way to check chip caps is to reflow the joints, one end at a time.
This usually shows up a broken component or detached metallisation.
Steve
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