More switchmode power supply grief - Cisco IGS router

[Peter Coghlan]

I have a Cisco IGS router which hasn't worked for a long time.  When I was
last using it several years ago, it occasionally crashed and restarted.
This turned out to be due to a poor contact on a connection in the
cable going from the output of the power supply to the main board.  I
cleaned the contact more than once but it was difficult to make it good
enough to ensure reliability.

When I switched it on more recently, it was completely dead, no LEDs, no fan
noise, no anything.  I put it in the naughty pile and it sat there for a few
years before I got around to looking at it.

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 :-(

There are lots of data sheets available for this power supply on the web
but they concentrate on the specifications for the unit and don't say
anything about the components :-(

There are also lots of people offering to sell power supplies like this
for way more than I am interested in spending on this project :-(

I could replace the power supply with a different one, however, I don't
have anything to hand that will fit in the approx 5-6cm headroom :-(

Anyone have any suggestions?

Regards,
Peter Coghlan.