"Maciej W. Rozycki" wrote: > On Thu, 3 Feb 2022, Peter Coghlan via cctalk wrote: > >> Today I finally managed to check it out. The ceramic F4A mains input fuse >> beside the power switch on the back panel had blown. When I opened it up, >> I found a POWER-ONE MAP80-4000 power supply. The main chopper transistor >> labelled Q1 on the PCB is almost a dead short. It is a large plastic >> packaged FET mounted on a piece of aluminium which is in turn screwed to >> the case for heatsinking. Unfortunately, there are no markings on it so >> I have no idea what to replace it with :-( >> >> As Q1 is shorted across all three terminals, whatever drives it may be >> damaged too :-( >> >> After finding screw heads hidden under the label, I managed to extract >> the PCB from the case and found some corrosion underneath, possibly from >> leaking electrolytic capacitors :-( > > This PSU seems to have been used across various Cisco devices and I had > one fail several years ago in a WS-C1202 Ethernet/FDDI switch, also having > suffered from leaking caps. Back then RS still had it in stock at a hefty > price of £489.60: <https://uk.rs-online.com/web/p/products/8338173/>, so I > chose to recap the failed one and thanfully it has continued working ever > since. You may try to enquire with the manufacturer. > > Good luck with bringing yours back to life! >
Thanks Maciej. I'll be surprised if the manufacturer has records of what they used for the chopper in power supplies 30 years ago - who knows if their design has changed between then and now. I'll be even more suprised if they will talk to me about it but I guess it's worth a try. Regards, Peter. > > FWIW, > > Maciej
