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How do I put this... You've been thrown in the deep end :-) Am I correct that your 11/24 is in the 10.5" (6U) box? Boards going in vertically from the top? If so, it is the PSU I am thinking of. I came across it in the 11/44, and it's one of the most complciatred PSUs you are likely to come across. It is a swtich mode unit. Or rather it's several switch-mode PSUs. The basic design is as follows : Incoming mains is rectified ans charges a pair of coke-can size capactiros at the left hand side. This provides about 350V DC which powers 3 SMSPUS sections : 1) A small one, to provide power for the PSU control electronics. 2) The 'logic' supply. This is an SMPSU which provides the main +5V rial and also +/-15V rails for the RS232 ports, etc 3) The 'memory' supply. This is another SMPSU,. giving 36V. This 36V rail can be battery-backed by an optional unit which you probbly don't have. The 36V is brought down to +5V, +12V and -12V for the memory boards by switchign regulators (non-isolting ones, of course). it's also chopped by a full-H circuit to provide power for the 35V 70Hz cooling fans. This is one of the few PDP11 supplies where the fans do nto run off the mains. A word of warning. If you remvoe the top cover from the PSU you will see barrier terminal blocks at the tops of some of the PCBs. In particualr there ar 2-way ones with red and black wires on 2 of the PCBs. These wires carry the 350V DC input, which is not isolated from the mains. Touch those with the mains connected and you won't feel anything. Ever again. Seriously, it could well be fatal. That said, it's a more friendly SMPSU than most, in that much of the control circuity is isolated from the mains (so you can connect a 'scope or whatever to it without problems) and scehamtics are avaialble. I am pretty sure this is the same supply... Actually, I don't think it does. I don't remember needing one when I repaired the PSU in my 11/44. Certianly I've never met a DEC-designed supply that is damaged by running on no load (the output votlages may be low or missing, bit it won't damage any parts), so it's safe to try it. But a dummmy load is not a bad idea, particularly on the main 5V rail (ffro mthe logic supply, rated at 125A or something similar). I don't know if the 11/24 is similar, but on the 11/44, this output is a pair of studs/nuts that flexiprint tails from the backplane go onto. I think i'd remove all the logic boards form the machine (keeping a note of their positions!), conenct, say, 30W or more of 6V bulbs across the logic supply 5V output and power up. Check all the voltages. If any are out of spec, try adding a load to them beforediving into the PSU internals. -tony