[sdiy] Amp / power transistor woes
stewpye at optusnet.com.au
Wed Jul 18 22:57:34 CEST 2012
On 7/18/2012 7:31 AM, DTK wrote:
> Each channel has 2 darlington pairs in a push-pull configuration. I
> can see how a failure in one channel would blow all the trannys in
> that channel, but the fact that I have issues in the other channel
> seems to point to some root cause common to both. As far as I can
> see, the only thing common to both channels is the power supply, so I
> suppose that's where I'll look next.
> Right after I pull and test all the other transistors, anyway.
The cause may be that there was a short on the output of the amp. (cable
or speaker). When the user didn't get any sound out of the first channel
they plugged it into the next and blew that one too.
Depending on how the transistors are soldered to the PCB sometimes it's
easiest to just desolder two leads (C, E) to test them. You'll also need
to check the driver transistors and resistor between the drivers and
output transistors. If in doubt replace the driver trannies. If the
driver trannies are blown keep going further down the line. Also check
all emitter resistors (with shorted transistors removed) and all small
value or fusible resistors and all diodes.
Make sure the transistors are insulated from the heatsink when you
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