The shop did not fix the preamp although they claimed that they did so... forget them. I'll try it myself (even though I have no idea what I'm doing). I took it apart at home and there were two pieces of bare aluminum wire connected (soldered) across the top of the pots - one on the top row and one on the bottom row. There was also two pieces of green wire soldered to the negative terminal of the VU meter and attached to the nearest pot (connecting all the potentiometers in series to ground via the VU meter negative). These components did not look factory so I removed them (they were present before I took it to the service shop too). Am I correct and okay to do this? The pots are grounded to the chassis via their mounting nuts anyway and by removing the additional grounding some of the noise the amp was making has been eliminated (although it still gets noisy with the gain turned up high). The buzz is less when the EQ stage is engaged.
Should I replace all the caps and if I do, is the rated operation temperature of the caps critical? What about the type of cap (aluminum electrolytic, film, copper, poly, etc.)? I hear Panasonic are good, but they have so many different "series" of caps. Which ones should I pick? I really don't know anything about them, but I can operate a soldering iron. It can't hurt to change them although I've read changing them may change the sound (color) of the pre-amp.
These are the radial caps that I found in the preamp:
Main circuit board
2200 microF @ 16V x1
100 microF @ 50V(RE) x2
4.7 microF @ 63V x2
10 microF @ 50V(LL) x2
22 microF @ 35V x1
47 microF @ 35V x2
Power supply board
220 microF @ 35V x2
2200 micro-M @ 25V x2 **What is micro-M?
100 micro-M @ 63V x4
220 microF @ 100V(RE) x1
