I've just ferreted out my list of people I knew when I was in the trade.
I knew I'd still got it somewhere.
This chap is of long experience, and should be able to help you if you get really stuck.
http://www.mikebarden.com/ He is a genuine, highly experienced engineer, not a dabbler.
I also tried searching for a service manual, and had no more success than Silvered Mica had.
Dry joints / poor connections are still the most likely bet (in my personal opinion). Tony.