11/45 lower regulator board

[Jay West]

Tony wrote....
> It's a right pain, isn't it!
...snip...
> Getting the H742 supplies out is a pain too, due to the fan wiring.
...snip...
> I seem to remeber unscrewing the _top_ H742 supply from the rack and
> moving it out of the way without disconnecting the fan wires (I think I
> had to unplug some of the mate-n-lock connectors). Then I could get to
> the screws in the lower supply.

I found a way without removing all the fans...

a 2x4 from side to side in the bottom of the rack, under the back half of 
the bottom H742. Then a few wood shims directly under the regulator tray. 
Then put a small 2x4 in front (and a wood shim or two) between the H742 and 
the 861. Disconnect all the plugs on the supply and unscrew all the fastners 
on the cables and the supply. Then you can slide it gently on the wood to 
the middle of the cabinet and you can easily get to the guts of the power 
control board. The power harness stays attached to the fans but can move 
with it if you undid all those fasteners too. A heavy screwdriver under the 
front, twisted slightly, to align the holes for rebolting it into the rack.

Phew. Now that I have the entire regulator board out, I can visually see the 
fuse F1 is clearly blown (and of course it tests open). I could just replace 
it, but something obviously caused it to blow. Once I put a new fuse in if 
it doesn't blow, what should I be looking for in that circuit? Also, 
couldn't I just plug 20-30vac from a bench supply into this linear supply 
and then check test points in the circuit? Given it's hard to reach 
location, that would make it easier to work on if it could be powered up on 
the bench.

Jay