> > Hi folks, > > I've begun repairing my PDP 11/40 and have tracked down the first major issue > to the H745 (-15v) regulator.
Before you dive into the brick (sounds painful!) check that the +15V DC input is present and correct. Unlike the +5V units (H744, etc) the H745 needs both the 20V AC from the transformer and a 15V supply which comes from either the PCB on top of the transformer (in an H742 supply used with the BA11-F) or the PCB under the transformer in the supply used with the BA11-K If that's OK, then it's the usual suspects in the brick. The capacitors can dry up. There is a fuse, but it never fails for no good reason, so if it is blown you need to find out why. Power semiconductors on the heatsink bracket. Whatever you do do not disable the overcurrent trip (e.g. by desoldering the collector of the sense transistor). If you do, and the crowbar fires then you will be cleaning bits of transistor off the ceiling. Do not ask how I found that out! -tony
