Sony Receiver STR-4800SD L/R Balance

[sretchko]

Hey fellow solder fume lovers, I have a Vintage Sony Receiver STR-4800 SD that has me stumped.
The Balance Pot has to be set at about 30 degrees (11 o'clock) to the left for the output to be balanced (see photo). I'm using an oscope, sig gen 1kHz sine, 8 ohm dummy load).

When output is balanced (11 o'clock left) both channels clip at about 19 vac / 45 watts RMS, Amp is rated at 35 watts so I know the amp modules are good. Square wave also looks good when turning bass & treble pots and is in phase.

I pulled the balance pot, (Dual 10K MN Taper) cleaned with Deoxit and resistance is balanced at center position and equal resistance full L/R. Problem remains…

I also pulled the speaker relay and cleaned it since I had the unit apart.

I checked every cap, resistor & Flat amp Q's in the balance and tone circuits and all are in spec.

Some amps I have worked on that have a balance control have to be tweaked a little L or R to balance on the scope, but 30 degrees makes me think something up or down stream is causing this?

Any thoughts, ideas, or specific knowledge would be greatly appreciated 😊
Thanks, Steve

PS. I have attached the service manual (p 23-24 for the tone board).

[CapLeaker]

Feed both L and R input at the same time with the signal genie, then poke around with the oscilloscope from the input through all the stages and compare L and R channels. Figure out on which stage of the amp the injected signal starts to differ in amplitude between the channels.
Btw same thing happening if you got headphones plugged in?

[sretchko]

CapLeaker, will do, thanks! It does the same with all inputs, phono, tape & aux. I haven't checked balance on headphone out but will do that when I get it back on the bench. Waiting on some LED lamps to be delivered