DEC H745 regulator common failure modes?

william degnan billdegnan at
Fri Nov 27 15:14:33 CST 2015

On Fri, Nov 27, 2015 at 1:09 PM, tony duell <ard at> wrote:

> > There is a pdp 11 troubleshooting guide on Bitsavers that covers the h742
> > powersupply and regulators 744. 745, 754.  Assuming that is what you
> have.
> >
> > They're all tough to work on especially the regulators but I agree with
> > Tony that you need to lock down the main suppl first.
> I am not sure what you mean by 'tough to work on'. If it's a physical
> access
> problem then what I did was to obtain a spare 8 pin mate-n-lock plug and
> socket and make up a pin-pin wired extension lead about 1m long. Then I
> can take the brick out of the PSU, connected it via the extension lead and
> be
> able to probe it. I normally sit it on top of the CPU box of my 11/45, you
> get
> easily enough air flow from the fans to run it for testing.
> If it's that the circuits are complicated, well, remember these are
> swtiching
> regulators (not linear) but are a lot more repairer-friendly than most
> in that nothing in the brick is directly connected to the mains.
> -tony

Tough-sh to physically work on/test.  These are not made for field service
IMHO, just swap out part.


More information about the cctech mailing list