Sony STR-6800SD help needed

[G7065]

Hoping for some help with this receiver.

I just picked it up and it's in generally good condition but has an annoying fault:

When running in FM Stereo, the right-hand speaker drops out (volume reduces but 90%) after 10 mins. This is at low-mid volume, so not pushing the unit hard. This only happens in FM Stereo (works fine in Aux and AM), and if I push the Mono button, both channels work fine. As soon as I switch back to Stereo, the right speaker drops.

There's no crackling at all, and it doesn't seem like a faulty switch as far as I can tell.

If I switch the unit off/on again the problem remains, but if I switch it off and unplug it for 10 mins, it will then run fine again for 10 mins.

I've read that it could be related to faulty 330k resistors in the FM Stereo Separation module (R257, R258), but I don't have enough experience to know if this would be the case given it's an intermittent fault. They don't show any obvious visual signs of overheating, and I don't want to pull them out for testing without first ruling out other possible causes.

Any 6800SD experts out there who can help?

 

[cademan]

Clean all pots and switches first with deox.

Clean the mono/stereo switch and the tape monitor switch/button.

When it drops out again, push or wiggle tape monitor and the mono/stereo.

Both channels work fine in mono so it's most likely a preamp problem and not a main amplifier problem.

 

[elvi]

if I remember correctly, mine did have dropouts on FM.
As a standard triage of all new to me gear, all contacts were well cleaned .

I did not have dropouts after.

Btw, a really nice powerful reciever.

 

[G7065]

No joy having cleaned the pots.

No difference when wiggling the mono button or other switches - no crackling or other sounds either.

I’ve read it could be down to FM trimmers needing cleaning and/or adjusting, and it could be those 330k resistors mentioned previously… any other suggestions out there?