Hello,

I have a C712 preamp from Mc Intosh. The right side stop working on stereo mode but will work on mono mode. All the pots (bass, volume, treble, balance...) look to be dirty because they make noise when I turn them. Don't know if it can be the problem. I am looking for help or a schematic... It was repaired few years ago by a "pro" for same problem.

thank you

My guess is that, if you have both channels working in Mono mode but not in Stereo mode, the problem is a dirty mode switch (mono/stereo selector). If the problem were "downstream" from the mode switch, the dead channel would stay inert regardless of the mode switch setting. Giving the mode switch a shot of Deoxit might cure the problem temporarily (while the cover is off, give each pot a dose of spray pot cleaner).

Is the preamp being used in a "challenging" environment (high ambient humidity, exposure to cooking vapors from kitchen, etc.)? If not the recurring problem could be just be poor-quality components. At one time McIntosh was a highly respected audio manufacturer, but I have lost track of them (we used their tube amps in avionics manufacturing test equipment eons ago) so am unfamiliar with their current reputation.

I have Deoxit at home. Will try to removed all switches and clean them. But I am still searching for schematic...

Thanks

:My guess is that, if you have both channels working in Mono mode but not in Stereo mode, the problem is a dirty mode switch (mono/stereo selector). If the problem were "downstream" from the mode switch, the dead channel would stay inert regardless of the mode switch setting. Giving the mode switch a shot of Deoxit might cure the problem temporarily (while the cover is off, give each pot a dose of spray pot cleaner).
:
:Is the preamp being used in a "challenging" environment (high ambient humidity, exposure to cooking vapors from kitchen, etc.)? If not the recurring problem could be just be poor-quality components. At one time McIntosh was a highly respected audio manufacturer, but I have lost track of them (we used their tube amps in avionics manufacturing test equipment eons ago) so am unfamiliar with their current reputation.
:

I don't know exactly how this preamp is put together, but you shouldn't have to actually remove the switches in order to treat them with cleaner. They are probably soldered directly to a printed circuit board, so removing them would be problematic. Just remove the outer case cover and squirt some Deoxit into the mechanism while working the switch.