Ok, back home, and thanks to all suggestions, I found the following. Barely visible is the writing H9270, so that clears up what backplane is installed in the card cage. The power supply is indeed an H780. I have a copy of "microcomputer handbook" 1976-77, and on page 2-4 at the bottom is figure 2-2 which shows (literally, table and text): A B C D ------------------+------------------ 1 | position 1 | position 2 | <--- positions 1 & 2 are ------------------+------------------ normally used for 2 | position 4 | position 3 | the processor module ------------------+------------------ in single backplane 3 | position 5 | position 6 | systems and the first ------------------+------------------ backplane in multiple 4 | position 8 | position 7 | backplane systems ------------------+------------------ Anyway, I was enough assured to apply power. Double joy, because the fans do not make an awful high pitched sound, just "normal" blowing, and I got on the terminal the output 173002 @ So, that looks like one more system in my collection :-) Lucky for me it is a small system. I need something more to make it usable. The RXV11 from Pete Collum crossed my mind ... thanks for all good info! - Henk, PA8PDP.