MINC-11 boot problems

Hi all, I obtained a MINC-11 from Adrians DEC emporium(aka garage) in Cambridge last year (http://www.binarydinosaurs.co.uk/museum/digital/minc/index.php). I've finally got around to taking a look and it appears to be complete and original with a /03 CPU. Taken all the cards out and given it a good clean. Checked for any odd washers etc. in the backplane. Removed the power supply (H786), hooked up to a pair of hard drives as a dummy load and tested. Nothing. Normally at this point I'd scrap it and hook up a PC PSU but I've been reading this group too long and have been persuaded by Tonys component level repair arguments so I got stuck in :) Tracked it down to one of a pair of 1N4004s connected in series after the 7912 12V start-up regulator. So, I now have healthy 5V & 12V supplies and these seem to be stable for a long time with all the cards in place. But - it's not booting. The diag LEDs on the BDV11-YA constantly read 1001 from power on (I'm assuming that on=1). The only table of diag codes that I could find lists 1001 as "DECnet message received" which I believe to be bogus since I don't have any DECnet cards (I'm also wondering if the MINC has different diag codes?). So I started digging further and found that BDCOK H is ~1.7V and BPOK H is ~2V. Now, I believe that these signals are generated directly from the PSU, specifically the power monitor board that calls them DC L and AC L. My assumption is that these should both be at 5V in a healthy system since they are active high - correct? Unlike a regular LSI11 the MINC doesn't have any front panel buttons or LEDs (e.g. for BDCOK status) so I can't easily tell if what I have is good or not... I've not gone too much further yet but thought I'd try and get some knowledgeable input to make sure I'm not going down the wrong path. One thing I have found is the -12V supply that's only used inside the PSU (and feeds the power monitor board) is at ~-15V. Many thanks for any advice! James