Purchased recently at garage sale ($60.00). Works fine until warm-up. Then randomly and intermittently changes Function. Sometimes can re-select desired function (Video for example); sometimes does not respond to function select. Stays locked in to some other function, Tape/MD for example. I have downloaded service manual. I suspect dirty/corroded contacts or contaminated circuit board conductors; will inspect.
Advice welcomed. (Audio enthusiast and repair since vacuum tube days). Aloha from Maui
