The electrolytic capacitors often fail Remember this system was built at the very end of the [https://en.wikipedia.org/wiki/Capacitor_plague|Capacitor Plague] I'm sure some bad parts lingered around a bit. See if any look puffy or leaky.
While a bit dangerous you might want to test the AC side of the supply to see if power is getting in and then check the voltage along the main rails to the DC side. Sometimes I find an oscilloscope can be helpful if one side of the AC to DC rectification is messed up.
Does the system respond in any way?