Good news! It looks like I have managed to get this working again. I realised I had not checked the electrolytic capacitors on the main logic board, ones situated far from the main power output boards. I found one which had a higher ESR than two other identical ones, although the ESR was still theoretically OK according to the table on my meter it was at the limit, so I replaced it and the PSU now appears to work. It really goes to show, *all* electrolytic capacitors should be checked. Picture showing the one I replaced here: http://1drv.ms/1PlfKIV.
Interestingly, I had had a similar failure in another of these PSUs, which I handed to a friend along with a VAX 4000-300 I gave him, in the hope that he would be able to fix it. As that PSU was already partially dismantled from my previous investigations, I asked to borrow it back for the purposes of doing the reverse engineering. I noticed that the same capacitor on that PSU also has a higher ESR, but again within range of what should be OK. So, looks like I might try this as a fix for the second bad PSU too, if he is OK with me trying that. Regards Rob
