PDP-11/34 PSU Yet Again

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Thu Mar 6 13:51:01 2003

> Ok, problem found: me. I got confused by the print set on the representation
> of front vs back views, and thus I had my regulator positions backwards. We

Wait until you sart populating a large backplane of flip-chips like an
RK11-C or worse a DX11. The printsets show the backplanes from the wiring
side you seen. Took me a bit of time to figure that one out (as in 'Hey,
why are all the PCBs in the wrong slots??').

> were both also confusing the H745 and H754. Everything (except one thing)
> looks fine now. Here's what I have:
>
> Under Xformer +15V
> Brick 1: H745 -15V
> Brick 2: H7441 +5V
> Brick 3: H7441 +5V
> Brick 4: H785 +5VB, +15VB, -15VB
>
> The H785 doesn't produce -5V or +20, so it is certainly OK that I'm not
> finding those voltages on the backplane power connectors!

Yep.

>
> My current understanding (no pun intended) of the H785 is that when it is
> not running off the battery, it produces +5VB, +15VB, and -15VB with current
> from the mains transformer. Am I correct?

I believe so. I've never had an 11/34 with the battery backup option though.

>
> My testing shows that I have the correct voltages on all the right pins,
> including -15V. However, the LED on the H745 (-15V) does not light. What
> does this mean?

The 'LED' runs straight off the output rail, so there's little that can
go wrong if the output is somewhere near -15V. Most likely you have one
of the older H745s with a light bulb not an LED, and the bulb has failed
(they do this from time to time ;-)). Or I suppose if you have an LED
that, or the series resistor, could be defective.

-tony
Received on Thu Mar 06 2003 - 13:51:01 GMT