"Tom Amundsen" wrote in message
...
I'm trying to repair a Bose amplifier from a '92 Audi. One MOSFET
is cracked and I want to replace it but Google has not been my
friend on identifying this. They are a TO-220 package size. Three
of them are marked ST 99103 137110 one is ST 99112 137110. No
numbers on the ST website are close to this. I'd like to get
something from Digi-Key since parts stores are rare here (except for
Radio Shack if they have something that would work). I also assume
I have to replace all four if I can't get an exact replacement. Any
help is greatly appreciated.

Thanks

Seems like the 99 whatever is the date code. The 137110 is probably the
part number, which is an in-house number? The manufacturer is obviously
ST, SGS Thomson.

As for replacing all four, it depends on how the FETs are used in the
amp. If they are used in pairs, one pair for each channel, then you
should be able to replace just a pair. But then nowadays I've seen car
amps with four output devices, in an H bridge configuration in each
channel, to get more power from the 12V. So you have to check to see
how they're used. And it's possible that some devices might be used to
convert the 12VDC up to a higher supply voltage, so the bad FET might be
in that circuit. If you can see audio across them, then that would
eliminate that possibility. That's the nice thing about stereo amps: if
one channel is still working, you can use it to compare the voltages in
the bad channel.

Tom Amundsen. E-mail: