More switchmode power supply grief - Cisco IGS router

[Peter Coghlan]

"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