Switch mode power supply. Diode is dead, what else?

[fastline]

This is sort of a blind question but I am working on a complex PS in which the main board is the PS board and it's partner board is the regulated voltages board. I found an IN4004 diode out in the main PS board. Apparently this PS blew the main fuse and shut down. My brother installed a new fuse and said it did not do squat.

I honestly cannot be certain of the location of the diode in the circuit and cannot draw this out due to components being in the way of seeing traces and no layout. I am just curious from the experienced, if you find a dead small diode (not a big power diode), does replacement usually fix things up or does that short in the diode usually cause other systems to fail? Also, is it common to have a diode to just fail for no apparent reason or should I be looking for some reason for it's failure?

I just hate to power this board up and risk more damage if I have not found all of my problem.

 

[Nigel Goodwin]

You need to identify where in the circuit the diode is - as it's a low speed diode, then it 'may' be part of the mains bridge rectifier, in which case you should replace all four of them. Generally this wouldn't cause any further damage, except perhaps blowing a surge limiter feeding the bridge, particularly if he's been replacing fuses and blowing them.

But I'll repeat, you need to know where the diode is in circuit, and what it does.

 

[fastline]

Well I know it is not part of the bridge. That is a module on the board. This PS will move a lot of power. 15A at 240V broke down into 8 difference DC voltages. The diode feeds a one of the taps on a a 16 pin transformer after rectification. That seems the trend I see on switch mode PSs but I honestly do not know what they are used. Possibly to keep voltage high through the bridge for more power, then buck it down as DC.