PDP-11/23 Debugging

[Glen Slick]

On Sun, Nov 16, 2014 at 7:44 PM, Ben Sinclair <bensinc at gmail.com> wrote:
> Well, I just discovered something interesting... What exactly does the aux
> switch on the front panel control? I assumed it was power to the AC plug on
> the back of the machine, but it must do something else. With aux in the
> down position, it again boots to XXDP! If I flip it up and restart, it
> drops back to ODT after trying to boot XXDP from the TU58.
>
> From the documentation, I don't see that it does anything other than
> control that AC plug.
>

Take a look at the 11/03-L Front Panel schematic on page 19 of this
scan of the BA11-S Field Maintenance Print Set:

http://www.bitsavers.org/pdf/dec/qbus/MP01233_BA11-S_schem_Mar81.pdf

If jumpers W1 and W2 are installed on the front panel PCB then the
BEVENT line will be pulled down to ground when the AUX switch is in
the OFF position and I believe that will disable the CPU from
receiving LTC interrupts.

Maybe your system is having issues handling LTC interrupts.

I have one BA11-S with jumpers W1 and W2 installed on the front panel
PCB and another one with those two jumpers removed, so check your
front panel PCB to be sure whether or not they are installed, but it
sounds like they must be in your case if the position of the AUX
switch causes a behavior change.

-Glen