Hello and thank you for your answer.

The resistance looking into the secondary outputs are as follows (with
unit unpowered of course);

+3,3V Output; 0,3 ohms (no change when reversing measuring probes)
+5V Output; 8 ohms (no change when reversing measuring probes)
+12V Output; 604 ohms (when reversing probes I get 100 ohms that rises
slowly to a few kohms)

The voltage at pin 4 of the KA7500B is 3,38 V without the green wire
connected to ground and 4,2 V with the green wire connected to ground.
I guess this indicates there are some bad secondary rectifiers in the
circuit? Should i go ahead and order some new rectifiers or are there
other things to check first?

Thanks again,
marty