NCR Tower PSU again

Hmm, getting somewhere; found a dead triac near the input which was supposed to bypass that 10 ohm resistor that was burning out once the PSU had started up. Presumably the intention was to allow the PSU to start a little more gracefully. Nice bodge story: I just found out why the system wasn't starting up at all. It had been semi-dismantled since it had died years ago; I'd reassembled it recently when trying to get it running again. After much wiring tracing I've just discovered although the cable between the control panel and the backplane is keyed at both ends, at one end the connector was on back to front. That hadn't stopped whoever assembled it at the factory from hammering the keyed connector backwards into its socket! I hadn't noticed how bent out of shape the socket was when I reassembled the machine; I'd simply lined up the key on the connector with the relevant slot on the socket, then spent ages trying to work out why the PSU wasn't even trying to start up when the switch was operated. Grrr! Now, I'm getting a good 5.1V output, but there's a nasty wheezing noise (not a whine!) from somewhere on the main PSU board. The +12V and -12V rails are seriously up the spout. With a light load (just a couple of fans), the fans spin up for a couple of seconds before everything shuts down for a couple more seconds, then the cycle repeats (the wheezing sounds like breathing at this point!). With no load the wheezing's constant and the PSU doesn't shut down, but -12V rail is at -4V and +12V rail is at +5.3V. I'm going to load the PSU up with an (unwanted) hard disk in a moment just in case it's not firing properly because of not enough load - not sure if I want to risk any boards in there at present though, but of course it's possible the PSU's not operating properly because there's some feedback from the absent CPU board not present... Any widsom appreciated. Sure don't like that wheezing noise - cap or wound component? Fault or just something not being driven at the right frequency? cheers Jules