Technical question - Pioneer SX-727

[Aja097]

I need some help and advices for servicing a 1973 SX 727 : I'm not a specialist but i found preamp output voltage too high for right channel : 9 volts compare to 170 mv on left channel, no input. ( taken beetwen points Lo 13 and 14 and Ro 13 and 12 on the control board)
Furthermore, switching on either mute or low filter control activate the protection relais, cuting sound for only some seconds.
Last, maybe related to problem above, there is a constant "hum" on right channel even with volume at minimum.
Any ideas ?
Thanks, Jerome

 

[EchoWars]

I don't have service data for that one...but obviously something is badly amiss.

 

[Aja097]

Neither do i ...Trying to get a manual, not easy to find one in Europe. Will post a scan of the preamp board when (and if !) i can ...
Thanks for your help.
Jerome