Major RS2020L

Check the power supply voltages to see if all circuits are getting proper voltage.

Check that all switches and knobs perform properly.

Check the antenna is in good shape and connected.

See if you can find the oscillator and check if it is working.

Does it produce any sound at all? Static hiss? Does the volume knob increase the hiss?

Caps may look OK,  but electrolytics deserve special scrutiny. 

Supply voltages are fine.

Switches and knobs works ok. I found one pot that is a bit "jittery" but it works.

I've exluded antenna and oscillator stage up to now, as this radio has an aux input on the back. I'm using that input to inject signals with a waveform generator (AC coupled). L/R signals arrive to the amplier board but only one channel is working. Volume knob changes signal amplitude on the working channel, the other output is dead. At the moment I'm using a scope to probe output signals, I've not connected any speaker yet. 

I managed to probe the base of the output transistor (high side) for both channels. The working one is at Vcc/2, while the other one is stuck at Vcc. I'm trying to work backward from that.

Than you for your kind suggestions!

Ok, I'll have a closer look. What should I look for? I can easily measure capacitance with my multimeter, but I don't have a LCR to check ESR.

Thank you!

I checked radiomuseum (which very often has circuit diagrams) but they have zero from that manufacturer. No photos of the interior are on their site either : ( 

When you removed the output transistor was the base signal still stuck at VCC?

I did not measure that without the output transistor. I'll have a look. I expect to find it stuck at Vcc as well, but we will see.

Thank you for having a look!