Hello everyone, while searching for a solution for my low volume problem I googled apon this thread (https://music-electronics-forum.com/...t=45628&page=2) which could potentially be the same solution for my problem. Obviously the models where different, so most likely it isn't, but the idea alone of the IC4 circuit and the Q4.
Heres the quote from the user g1:
"In any case, like Jazz said, it looks like you are losing signal before the output IC, and you said it is weak even using the aux in.That narrows it down quite a bit, IC4 and Q4 areas.What is the gate voltage at Q4 ? "
"At this point, if it were me, I'd clip Q4 off as close to the board as possible and see if the sound comes back. Hopefully the legs are long enough that it can be re-used if it does not solve the problem. It could be something else in the Q4 circuit, but my experience has been that it's more often the fet than the circuit. Then if the sound comes back you can measure the spot on the board where the gate was. If the +.5VDC is still there, there is some other problem in the Q4 circuitry."
This worked for the user and the problem was fixed. Now I did finally find a schematic for the FM25 DSP and it was thanks to that thread. So in my search to see where this IC4 and the possible culprit Q4 is located on my board, and low and behold there is no Q4. So my symptoms are the same to the original FM25R thread. I would like to add that before this low volume issue arose, the amp would start to distort or fuzz ever so slightly with the signal to the output. Then a few more times later the amp started to fuzz out the signal to the point where it removed the amplitude of the sound as if it was being choked. Then it happened. "LOW VOLUME".
I look forward to all your advise or help that you can offer, because from what I have read so far your all talented buckets of knowledge and I really really really want to fix this amp.
Here is the link to the FM25 R schematic from the original thread, https://music-electronics-forum.com/...4&d=1514322135
Here is the link to my board, http://bee.mif.pg.gda.pl/ciasteczkow..._Schematic.pdf
Heres the quote from the user g1:
"In any case, like Jazz said, it looks like you are losing signal before the output IC, and you said it is weak even using the aux in.That narrows it down quite a bit, IC4 and Q4 areas.What is the gate voltage at Q4 ? "
"At this point, if it were me, I'd clip Q4 off as close to the board as possible and see if the sound comes back. Hopefully the legs are long enough that it can be re-used if it does not solve the problem. It could be something else in the Q4 circuit, but my experience has been that it's more often the fet than the circuit. Then if the sound comes back you can measure the spot on the board where the gate was. If the +.5VDC is still there, there is some other problem in the Q4 circuitry."
This worked for the user and the problem was fixed. Now I did finally find a schematic for the FM25 DSP and it was thanks to that thread. So in my search to see where this IC4 and the possible culprit Q4 is located on my board, and low and behold there is no Q4. So my symptoms are the same to the original FM25R thread. I would like to add that before this low volume issue arose, the amp would start to distort or fuzz ever so slightly with the signal to the output. Then a few more times later the amp started to fuzz out the signal to the point where it removed the amplitude of the sound as if it was being choked. Then it happened. "LOW VOLUME".
I look forward to all your advise or help that you can offer, because from what I have read so far your all talented buckets of knowledge and I really really really want to fix this amp.
Here is the link to the FM25 R schematic from the original thread, https://music-electronics-forum.com/...4&d=1514322135
Here is the link to my board, http://bee.mif.pg.gda.pl/ciasteczkow..._Schematic.pdf
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