PDP-11/10 PSU Repair/Warning

[Noel Chiappa]

    > From: Systems_Glitch

    > I believe the big difference was in the current-supplying capability on
    > the +15V rail -- 1A vs. 4A.

Ah, thanks for the tip.

I have an H742, so I was exable to examine it, and the 5409730 (difference
details on that below). The transformer may also be different (see below).
The other differences seem to be mechanical; a larger cooling fan on the 7420,
and the sheet-metal enclosure that holds the the power control board,
transformer and fan is in two parts, bolted together.

Interestingly, in light of your issue, the H7420's all have a fuse in the AC
supply line to the 5411086; it's mounted on the enclosure. Nothing in the
H742, though.

    > I believe it was mentioned as an upgrade thing in one of the technical
    > manuals I'd read some time ago.

If you happen to recall where that was, I'd be very interested to see it.

Upgrading from an H742 to an H7420 appears to be relatively simple; the pinout
on the Mate-N-Lok which carries the outputs from the power board (DEC's name
for it changes) is the same in both versions. (Have yet to look at the two
Mate-N-Lok's on either side of it; I guess those carry the ~30V AC to the
bricks.)

Upgrading an H742 _to_ an H7420 appears to be more problematic. To start with,
the power board is mounted vertically (on the inside face of the enclosure) in
the H7420, but horizontally (above the transformer) in the H742. Maybe they
changed the transformer too? Will have to check. It's also possible that was
caused by the switch to the larger fan. Anyway, the 5411086 might not fit
in the horizontal; plus the interface is different (see below).

    > It would be easy to make up a new harness to swap one in place of the
    > other, since the 5411086 goes to a Mate-n-Lok that plugs into the power
    > distribution board.

Yes and no!

The 5409730 and the 5411086 are significantly different, mechanically. The
former doesn't have the edge connector (the one that burned out on you),
rather it has a short 12-wire pigtail to a female Mate-N-Lok which plugs into
a hole in the enclosure. That's for the _outputs_ - the AC input is in a
separate 4-pin Mate-n-Lok (physically exactly like the one on older disk
drives on PC's) which is mounted onto the board. (4 pins since there are two
differnet AC inputs - one pair is filtered through what seem to be hefty coils
in the input wiring.)

The harness used in the BA11-K is also significantly different from the one in
the H7420; the former has a male Mate-n-Lok, the latter is a female. The
pinout appears to be a subset on the BA11-K, only 9 of the 12 pins are wired;
assuming standard colour coding, the +8V DC is missing, as is the second 
ACLO and DCLO.

Although, as you say, one could make a new harness. Speaking of which, do you
know of a source for the connector that goes onto the edge connector? (Some of
my BA11-K's are missing the harness.)


I'm slowly adding all this info to the CHWiki.

    Noel