PDP 11/24 - A Step Backwards

Tony Duell ard.p850ug1 at gmail.com
Wed Mar 30 22:25:39 CDT 2022

On Thu, Mar 31, 2022 at 3:52 AM Noel Chiappa via cctalk
<cctalk at classiccmp.org> wrote:

> If the machine then runs, it's up to you as to whether you get the P/S
> repaired so that ACLO work properly - your call. (I wonder how the -15V got
> to ACLO - I suspect a solder bridge from the prior repair - but knowing the
> answer is not important to getting the machine running.)

A short in FET Q15 on the bias/interface board in the PSU could do it.
The gate of that FET is driven from an LM339 comparator the -ve supply
of which is -15V.

Of course _why_ Q15 failed, if it has, is another matter.


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