On Jun 8 2006, 17:15, asbesto wrote: Is it missing or just not working? It's hard to imagine a BA11-N box like the one in your picture without the PSU, since the screws that hold the front panel onto the backplane go through the PSU cover. If it's simply not working, it's not usually hard to repair. You will need to ensure that the BDCOK H (Bus DC OK, active high) signal is held high, also the BPOK H (Bus Power OK, active high, from the AC input) signal or the CPU won't run -- the normal PSU does this. "High" means tied to no less than 3.5V DC. The PSU also provides a mains-frequency square-wave at about 3.5V-4V which drives the BEVENT L line for a real-time clock interrupt, which Unix needs. One of the switches on the front panel can be configured to control this (there are times when you might want to switch it off). Note that devices that turn off BEVENT, including the switch on the front panel, or the DIP switch on the CPU card, do it by shorting that line to ground! The same switch that can be configured to stop the BEVENT signal, is also often used to control the rack's power controller via a 3-wire cable with a 3-pin AMP Mate-N-Lok connector on each end. The front panel with the three switches also has a flip-flop controlled by one of the switches, connected to the BHALT L line, and another connected by a flip-flop to BINIT L. The first halts the CPU when enabled (active low), the other provides a pulse to start it. The RUN light on the panel is driven by the SRUN L signal on the first slot in the backplane. Most of the signals I've mentioned are carried between the backplane and the panel by a narrow ribbon cable. The backplane pinout is shown in a PostScript file called QBusConnsBig.ps on my web page at http://www.dunnington.u-net.com/public/PDP-11/ QBusConns.ps is the same file, but actual size, if you want to hold it up against the backplane. Nothing later than about 7th Edition, because BSD needs separate I&D space, which an 11/23 doesn't have (2.9 BSD might work, I can't remember). BSD (any version) is much too big for a single RL02 anyway. 7th Edition works; my original PDP-11 Unix system is my second 11/23, still in its original condition, which looks rather like yours, except it has two RL02s and a slightly earlier front panel. Be aware that the RL11/RLV11/RLV12 driver was not a standard feature of 7th Edition, though. You ought to do an inventory of the cards. 7th Edition wants at least 256K of memory. You might also want to see what version of the CPU you have. -- Pete Peter Turnbull Network Manager University of York