Ah, right you are; I'm not familiar with the M9312 codes (you seem to have that all well in hand :-), I've only studied the M873 and M9301 codes. But the M9301 'console without testing' code does in fact look like it would run without any memory in the machine. (Which explains some odd features in the code - I'd always wondered about the 'unusual' subroutine caling sequence, but now I see it allows it to work without any memory.) Not that I am aware of - see the power circuitry in the drawings, MP-00742, pg. 25. Maybe you're thinking of the M7891 (MS11-L), which does have such a jumper? Actually, having looked at the prints, it also uses either -5V or -12V/-15V (there's a jumper). So you might want to figure out i) which your system has (in a BA11-K box, if you have an H745 'brick' you will have -15V, if an H754 -5V; if a BA11-L box, different versions of the H777 provide different voltages, but I'm too lazy to check :-), and ii) check to make sure the - voltage is good too. Although I doubt the - voltage is causing this problem; I'm pretty sure only the memory chips use it, so it's it's not right, probably the memory would return bad data, is all. Noel