Roland JC-120 buzz in left speaker only

[Sparrows78]

Hi all,

I have a Roland JC-120 fourth edition with a tiny high freq buzz in left speaker only. It's not loud but I'm trying to identify the source of the noise. I recorded both speakers so that maybe someone more experienced than me can tell if the noise is "typical" and pointing to a certain problem?
There is a low 60Hz hum in both speakers but the high freq buzz is only in the left.
Everything else is working on the amp. Left speaker is fed by second power amp on schematic. The noise is there even with bypassed preamps. The preamps sound fine by themself, when tapping their outputs before the power amps.
I attach both recordings and schematic.

All inputs are welcomed

[Jon Snell]

If you insert an empty jack plug into the main in socket, does the hum stop?

[x-pro]

It looks more like an open input of an amplifier without a shunt resistor.
Check: points on board 9 and 10 of Main in Left.Ch. connector, R61, R33, R83

[Sparrows78]

If you insert an empty jack plug into the main in socket, does the hum stop?

No, it’s still there, unaffected.

[Sparrows78]

It looks more like an open input of an amplifier without a shunt resistor.
Check: points on board 9 and 10 of Main in Left.Ch. connector, R61, R33, R83

I will check these points, thanks for your input.