Sony STR-6800 SD - diagnosis needed

[jdelange]

Hi, I am trying to get a Sony STR-6800 SD receiver to work. Symptoms are:

1. Sometimes switching to FM engagages the protection relay (sound is interrupted), switching to another source resets the relay
2. Sometimes invoking the muting button on the tuner part (i.e. muting on) engages the protection relay
3. Without the muting button on, there is no stereo sound and the stereo light is off, engaging the muting button gives stereo sound with stereo light (if it does not invoke the protection relay)
4. Sometimes invoking the muting button results in distorted sound, switching muting off returns to distortion free mono sound
5. Most often, invoking the dolby switch engages the protection relay, though there are times that it works and the dolby light comes on

There are no sound / amp issues, when it plays, it plays fine.

It seems that the FM module influences the working of the protection relay (AM works fine). I noticed that the power supply winding used by meter lighting and Dolby circuit is shared with the mains switch off detection of the protection relay network (T11). My initial guess was therefore a power supply issue in this circuit, but I can't find any obvious clues. The schematic does not say what the AC voltage should be. I would not be surprised if some caps have died, but which ones to check?

Who can provide a diagnosis? Thanks, Jan

 

[Binkman]

Greetings;
Imo; diagnosis is just replace all the caps except the FM/am stage. However, I don't think this is a very good model w/o a decent SM. perhaps another model w/similar layout and transistors. but good to learn on. near complete work out as 1976-'78.. 40 years old.