Here's a link from the Vintage Knob.
  This is my third attempt to check out a vintage quadraphonic receiver, after the Marantz 4400 (Vladimir wasn't enthusiastic about trying to fix it), and more recently, the Harman Kardon 900+ (way too problematic and expensive to fix). I knew it powered up, but bought this beauty as is, and so far there's only weak sound in one channel. It's next for repair. I'll keep you posted.   It did clean up nicely, though.