But the HPIB connecotr and the expansion slot connecotrs are present? What does the power switch on the front feel like? Any 'click'? Ihe Inbtegral PSU is a single PCB that mounts in the bottom chassis. The power switch is soldered on this PCB, the IEC mains input plug is part of a filter unit that's fixed ot the back panel of the lower chassis and is conencted ot the PCB by a couple of wires and faston terminals. But I think you wouild see the PCB and components through the hole. Sounds like the entire PSU is missing. YEs, the are a bit of a fiddle. The service manual is on bitsavers, but I find it's easier to take it apart in the following way : Open the top, repmveo keyboard, anything stored next to the printer (mouse, etc), ink cartrridge (naughty -- do not leave that in the machine). Remove the expansion PCBs or slot covers. Remove the rear panel, take out the ROM module, take off the rear screening plate Disconnect the 2 cables form the floppy drive. Take out the 3 screws (2 in the well next to the printer, on at the bottom, going into the bottom chassis) that hold the drive in place and slide it out. Recover the eject button and spring Remove the screws hodling the logic chassis in place (2 of them are hex spacers). Easy it up and unplug the cable form the back of the display. Unplug the cables at the bottom edge of the PCBs. Ease it out further, remove the screen from the Logic B (front logic) PCB, then disconenct all the cables to the THinkjet mechanism. Tale out the logic assembly. The rear PCB (Logic A) contains the CPU, memory management, ROM socket, RAM and HP-HIL circuits. The front PCB (Logic B) contains the rest of the I/O -- HPIB, floppy controlelr, display controller, HPIL/Thinkjet interface, sound generator, real time clock. Undo the nut visible through the expansion conenctor PCB. This is a right pain to get back, but it has to come off. Take out the 4 screws and slide out the bottom chassis. Undo all the nuts and screws holding the cover on the bottom chassis (notice the empty screwhole, it takes a scre that holds the floppy drive bracket in place). Ease off the cover, it helps to remove the jackposts fro mthe HPIN copnenctor and recover the bracket and connector parts from inside the chassis. You can now see the PSU. -tony