the 763 is notoriously failure prone. It is the low voltage caps in the regulated low voltage rails, which is generally the culprit. It’s the thing known as ’the capacitor plague’. Many companies were bit by it, to the tune of billions of dollars of A/V gear tossed due to bad caps.
https://en.wikipedia.org/wiki/Capacitor_plague
https://en.wikipedia.org/wiki/Capacitor_plague