rockola 496 voltage regulator?

I have one working and one non-working 496 in the house at this time plus one extra power supply I picked up on Ebay. The non working unit appears to have an issue with the 26 volt supply. I've already ruled out the rectifier board and cleaned the connections. The extra PS I picked up seems to have the same issue, but it did arrive really beat up in shipping so I can't be sure anything in it works. I suspect the 26v regulator and I plan to remove the good power supply from the working 496 to compare them. I have the wiring diagram but I admit it doesn't mean much to me. So if I have them side by side how and where should I test to determine where the problem is?
Patrick