Yep, I've already checked out the rest of the voltages thru the machine. The AC inputs are correct, +15 is good, +5 is a little high at 5.5v but workable and I'll tweak it later, -5 is good, etc.
Just the darn 745 module. Fuse and connector are okay as well, no obvious signs of catastrophic failure. Sent from my iPhone On Nov 27, 2015, at 05:01, tony duell <a...@p850ug1.demon.co.uk> wrote: >> >> 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
