Ok, I will check all voltage first and then check also connection on a back side of IO board- but there are so many cables connected.. it is not quick job.
For me also is not logical that this overheating cause the problem on processor board.. but anyway
this overheating is not good and need to find the reason for that.
It will be good to have a electic plan of IO board if somebody have it???
Cable 880 is 110VAC to the spindle head solenoids, page 113 in the 1993 manual. These solenoids operate the piston for the tool release.
160VDC is the nominal, there is a transistor on the servo power board that dumps the extra into the large power resistor mounted below the servo boards (on a '91). Bad place for it as it then heats up the servo boards. I relocated mine on top of the cabinet inside a duct with a fan. Later machines use cook top heating elements, much cheaper than the power resistor. They are mounted in a cage with a fan on top of the cabinet.
Check the transformer connections are right for your AC supply. There are several options of taps.