Quick update before heading to the office...

Finally decided to check out the PSU (after managing to extract the other end of its #*@& captive connector from somewhere deep in the control/video board cluster). Lo and behold, one of the green 100uF caps had gunked up and seriously corroded the -30V and one of the neighbouring 4VAC traces.

How the PSU still managed to output the correct voltages (at least unloaded) is beyond me. Kudos to those Mitsu engineers, I guess. The caps incidentally check out fine with an ESR meter.

I guess the lesson learned here is not to blindly trust your scope and other gear! :^\

Will replace the caps and bridge the traces, then see what happens.

See ya,

--Roland