Power supply debugging advice (Interact Model One)

I am goign to assume that the service manual on that site applies to your amchine, nd that the schematics in said manual are therefore helpful. The poser supply is quite simple. The wallwart is, as you suggest, almost certainly jsut a transformer 9Well, maybe fuses too, we can always hope...). The outp[uts are bridge rectifierd, smoothed and fed to 3 terminal regulators to get the regualted votlages for the rest of the machine. When you say the 5V soems up fro a few seconds if the machine has been off for some time, does that mena if you then power cycle it the 5V lien comes up and stays up? Or waht? I would start by checkign the input to the 5V regualtor (probably a 7805). Yoiu need abotu 8V there to get the 5V output. Does that come up and stay up? Then try lifitng the output lead of the 7805 (look at a data sheet to see whic hthat is, and whatever you do make sure the common lead -- the one in the middle -- si correctly ocnencted . If not the machien will get the unregualted inptu votlage -- OUCH!), and connect an ammeter in sereis with it -- +ve side of the ammeter to the 7805 output lead and -ve side ot the track on the PCB. Power up, What sort of current do you see? Is it excessive (more than 1A)? If so, you have a short somwehre. Otherwise the 7805 iteslfe is a liekly suspect. They are cheap and easy to find. But those 3 terminal regulators ahve an interesting property that cuaught me once. If at switch-on the output pin is -ve wrt the common pin (it can happen), the thign will shut down. Is it possible the -12V supply is coming up first and due to some problem the 5V rail is going momentarily -ve? -tony