I'm attempting to fix a Royal Orca 3500 5-sheet crosscut paper
shredder that's eating fuses within half a second in either forward or
reverse directions. I was unable to find a 125V 3.5A mini glass fuse
in this size, so I replaced hte original with a 125V Littelfuse 3.5A
Picofuse.

I've testing various diodes on the board -- the 4 rectifier diodes
appear to be ok, but there are several others... many of which test at
a relatively low resistance in the reverse direction when tested
in-circuit. Without reverse engineering the schematic off this board,
or desoldering a bunch, I can't say for sure, but this appears to be a
Very Bad Thing telling me it's time to send this thing off to the
local landfill (though with the heft of that cutter, the tree hugger
in me would like to restore it to life if at all possible).

I have 3 questions:
Are these circuits likely to have diodes in parallel with a
resistive path (i.e. is it posible the diodes could be ok)?

Does anyone know if Royal actually stocks replacement boards
for these things?

Curiosity--anyone know the most likely root-cause failure
modes in these circuits?

The circuit in this one has one dual op amp, big diodes, little
diodes, electrolytic caps, 2 high power resistors, bunch a little
ones, 5 transistors, and a blue, square RW-SS-124D--apparently a
relay--likely for the overload protection circuitry is claims to have.

TIA for any info or shared experience!

Best Regards,
--
Todd H.
http://www.toddh.net/