R85 loud hum

[ven]

I recently acquired an R85 that I am cleaning up. I have replaced the needle, belt and optical sensor. Whenever it is not playing a record there is a VERY loud hum that goes away as soon as the needle touches a record(then it sounds great) There is a light indicating Left Channel overload in the amplifier lit. Is this a bad transistor? Any way to test? It even hums when the power switch is turned off (though not as loud) requiring me to unplug it.

Update: I tested all transistors and they are functioning. One thing I did notice is if I pull the volume control connection hum goes away but so does the sound. I pulled the preamp circuit board and drivers all resistors and caps look fine. Waiting for a service manual for specs to test those. Any help would be greatly appreciated.

[wdln]

You said the left channel shows an overload. Is that when it's humming or when it's playing? Do both channels have good sound when it's playing a record?

Seems like an issue with the muting circuit, like it's not muting the amp when a record isn't playing. Once you get the manual/schematic, that's where I'd start. You could also test to see if the amp isn't muting... with it just sitting there, gently rub the needle with your finger. If you hear it through the hum, the amp isn't muted. I think I'd also look for any ground wires between the mechanism chassis, power supply and amp that have been removed, disconnected, or cut.