Hi



I am currently attempting to repair my Creative Labs Desktop Theatre
amplifier, I am getting no output from the Subwoofer channel, if you run the
speaker test this again provides white noise in turn on each channel but no
output on the subwoofer. (Yes I have confirmed that the speaker is working
ok)



Unlike the other 5 channels the subwoofer does have a line out, if I connect
an amplifier and speaker to the subwoofer line output and run the speaker
test I do get output on all 6 channels therefore I believe the decoder card
is working correctly.



I have dismantled the unit and checked all connections they visually appear
to be ok, also the unit is on two PCB's a decoder pcb and the 6 channel
amplifier pcb, the subwoofer line out is also on the amplifier pcb therefore
the signal must be getting that far.



If I touch the input pin of the subwoofer power amp IC I get the expected
mains buzz, therefore I am fairly happy that the power amp chip is working.
Therefore it must be in the preamp stage someware.



I did try to obtain the circuit diagram from Creative but they said,
"Unfortunately I cannot give you a circuit diagram of the amplifier. We
don't supply this kind of information" which was polite but not very useful.



Before I sit down at attempt to trace the circuit out I was wondering if
anyone had already done this. Also each channel has an 8 pin IC marked 072D
and JRC, I dont recognise JRC but I am wondering if it is a dual opamp like
a TL072, from what I have traced of the circuit so far it does look
possible.



Has anyone had any experience repairing one of these, or recognise the chip.



Thanks

Dave