super jumbo

I was originally going after a Promax for 120, but that offer ended. I found another one that is in poorer visual condition. Deck B cover, two EQ sliders and one aerial are missing. The salesman states that only the right channel works, but from the image it looks like both channels are getting...

In a local auction I found a nice looking one, a Super Jumbo with all it's parts. The seller states that it "sometimes works and sometimes it does not" and that the cassette deck belts have crumbled from age. The second one I can fix no problem, but I would need to know why it refuses to work...