Re: Issue with Pioneer Quad 949A reciever
I also have one of those 949s - must be from aound 1979.
I doubt this will help much with your problem but... mine did the same thing after using it more than 20 years; I would get so frustrated, but it was worth the frustration and effort. Finally I disconnected and stored it for about two years, replacing it with an even-older Fisher 504 that I had that still works.
About two years later, I set up the Pioneer 949 again and it worked fine, and has continued to without that problem for at least the last four years. I am thinking humidity or dust had something to do with it. It has great sound even today and I still have the now-yellowed owner's manual!