H786 power supply help wanted

[Charles]

I have a PDP-11/23+ and the power supply (H786) "last ran when parked" a 
year or so ago. But there's no DC output at all today, and the fans are 
running so there is AC power...
I also have the original H7861 that came with it, which had a blown chopper 
transistor. I couldn't find anything else bad, so I replaced the transistor 
and within a few seconds of running, it blew again. :(

So I need some help - I've never been good at fixing switching supplies, not 
to mention the high-side hazards.
The simplest solution would be just to replace it with a working unit. 
Anyone got one to sell, hopefully cheap? :)
If not, can anyone fix one or both of mine?

thanks!
Charles