"Circuit" wrote in message
...
I am repairing this amp which is using the Tripath TA0104 preamp chip. The
output transistors are STW38NB20's (W38NB20) . I have found a supplier with
the transistors in stock. At least one is shorted from what looks like a
liquid spill near the heatsink where they mount onto.
When powered up, and input signal applied, I can see the LED-VU levels
bounce on both the input and output monitoring. There is a green LED near
the tripath chip which is not lit, labeled 'run'. Does this mean the
Tripath chip is not running and ought to be replaced? I have read about
some replacements for this chip which are inconclusive. Ought I just
replace it, or is the run light a sign its bad? Nothing else seems burnt,
but there are 2 black color hi-watt resistors that dont seem to have any
resistance at all, and may be open, but I need to remove them from the
board to be sure. They are shown in the photo below each channels power
transistors. No schematics - Thanks for any input.
Image of amp's mainboard:
http://www.imagechicken.com/uploads/...5039779400.jpg
Without getting into a drawn-out ****ing contest about the definition of a
'digital' amplifier, be aware that Tripath devices are not analogue in the
conventional sense that you might be used to working with on high power band
equipment. They are a form of switch-mode or PWM driver or amplifier, which
they as a company define as "digital". From my experiences with them, they
are difficult to apply 'conventional' fault-finding techniques to, and are
notoriously fickle on whether they decide to work or not, whether they
decide to fail or not when the output switching FETs on the end of them go
short, and whether or not they decide to re-**** the output FETs after
you've replaced them (either immediately, or after just long enough a period
to make you think you've fixed the thing ... !! )
You might be lucky. Sometimes it all works out just as you hope and expect,
but other times it doesn't. I'll wish you good luck, 'coz you might just
need it ... :-\
Arfa