Hi Tony Duell. Could you remember this thread below ? I have the same system and need some help to reassemble an HP tape drive. After disassembling and ultrasonic cleaning of a HP-Tape-Drive for this HP9915B two parts remaining unassembled. Two parts, small thin chromium-plated metal stripes, are droped down out of the device during dismantling. I could not find out where these have to be mounted again. Here you could see few pictures of these parts. http://www.nadhh.hanse.de/CMuseum/HP/HPTapeHilfe.htm I would be really happily if someone could help me to get out where these parts has to be placed back into that tape-drive. Could you help me ? With regrads j?rgen I guess I should respond :-). I don't know anything about the 9915B, but I have a reverse-engineered schematic of the 9915A, and from what yuo say below the PSUs are very similar. (Incidentally, the 9915A schematic is on the HPCC scheamtics CD-ROM, should you want it) 85B Ouch! I am going to assume it _is_ the same PSU as the 9915A. From what you say there, it's clear that the crowbar (Q4) hasn't fired, since this shorts the 32V (Vin, on my diagram) line to ground. My diagram shows U30 as an SG3524, but that may be because it had a custom HP number on it, and I found it was pinout- and functionally- identical to the 3524... Should be a potted-down version of the 12V line, If that's missing, then pin 1 will be olow. Potted sown from the Vref ouput (pin 16 This is called 'comp' on the 3524 datasheet. It's the output of the error amplifier and what's worth knowing at this point is that it can be pulled low exernally to shut the outputs down. OK, so the oscillator is running (that's the timing capacitor pin). And the reference output is also present. U30 may well be good. Outputs to the chopper (collectors of the output transistors, the emitters (pins 11 and 14) are grounded). It's clear the chopper is not being driven. R23 That's the first compoent reference difference (or I've made a mistake). On my diagram, C20 is the dcoupling cap on the V+ (pin 15) supply input to U30. There is a compenstation network, 0.1uF in series with 8.25k between pin 0 and pin 1, though. goes Ah.... Q2 is the overcurrent protection transsitor. It's turned on by U31 (LM311 comparator), which is driven from T1 (9100-0456 transformer) which measures the current through the chopper. If that current is too high, then U31 triggers, turns on Q2, and shuts the supply down. Whatever you do, don't disable this circuit. If there is a short, the results will be spectacular and expensive. Watch out!. Q5 is not a simple transsitor (at least not in the 9915A). It's a PIC645, which seems to be some kind of darlington with the flyback diode, etc, in the package. It's roughly a PNP transistor, emitter to Vin via T1 primary (current sense), collector to pin 3 of T2 (12V supply transformer primary tap), base to the output of U30 via that 820R resistor. No, Q5 is more than one transsitor. OK, what I'd do next is look at U31 (assumeing it's a 311 comaparator). The -ve input should be at about 2V (potted down from Vref again), the _ve input should be 0 (it comes from the sense transformer, but with no AC current flowing through the chopper, it can't be doing much). Then see if Q2 really is turned on, or shorted, or what. controller, Hope that helps -tony