Shugart 851 power problem

Don't know how to identify a switcher, but here are the specs: The whole box is Xerox product code F10, model 820. The PS has a sticker which reads: ASTEC AA11860 XEROX 105P80399. The sticker is all preprinted, that is, it does not give the impression that those are serial numbers. The PS is one board, with one transformer, about 1 1/2" across the windings and another, much smaller, about 3/4" across the windings. There are three cans about the size of AA batteries, five cans about the size of my thumb and three smaller cans. No signs of leaks. There is a fuse marked 2 1/2 Amp, 250 Volts which seems to be in good shape. There is a sticker which reads: "CAUTION Hazard of electric shock - heatsink is LIVE". There are transistors and diodes attached to the sinks and of course there are resistors and other components too numerous to list. Nothing looks burnt, charred or popped. Here ya go: (By the way, this is measured using the solder pads where the DC socket is connected to the 851 and is the same on both.) #1 IMSAI on and booted into Cromemco RDOS, drives off: 5 volt line reads 1.2 -5 volt line reads 0.0 24 volt line reads 0.6 #2 Next, turn drives on: Same as #1 #3 Turn IMSAI off: 5 volt line reads 4.9 -5 volt line reads -4.9 24 volt line reads 23.7 #4 Turn IMSAI back on: 5 volt line reads 5.0 -5 volt line reads -5.0 24 volt line reads 24.0