First, note where the boards went then pull them out (carefully, those pins can be stubborn and can loosed from the backplane). Next check the power supplies. I have seen an old OSI supply put out 7V where it should have been 5V: that would be a disaster. The fact that someone put voltmeters in the case probably shows some paranoia in this respect! Next, try re-installing boards and if you get lucky, it might just display "D/C/W/M" or rather "H/D/M" on the screen when it boots. The 505 CPU has only one ROM (not BASIC in ROM like many OSI systems did) and so is strictly disk-based (hence the prompt H/D/M). If the video works, try to boot a disk. If it fails to show video, or the video looks completely scrambled with random characters, a likely culprit is memory: in many old OSI systems you see bad RAM that just seems to appear from nowhere. The 527 uses 2114's which are common at least. If you get video, but not much else, you can try using the machine-code monitor (M) to diagnose the memory ... bitsavers probably has a doc on the OS65V monitor which will help (they were all about the same on OSI machines). Professor Mark Csele, P.Eng. Niagara College, Canada 300 Woodlawn Rd., L-23 Welland, ON, L3C 7L3 (905) 735-2211 x.7629 E-Mail: mcsele at niagarac.on.ca URL: http://technology.niagarac.on.ca/people/mcsele Author of "Fundamentals of Light Sources and Lasers", Wiley, 2004