PDP 11/24 - A Step Backwards

Rob Jarratt robert.jarratt at ntlworld.com
Wed Mar 30 16:29:32 CDT 2022

I found these two signals and ACLO is low (-15V) so I guess this must be the problem and whatever blew inside the PSU is probably the reason this signal is low. DCLO is high and the DC ON light is illuminated, but the CPU doesn't do anything presumably because ACLO is asserted.



> -----Original Message-----
> From: Tony Duell <ard.p850ug1 at gmail.com>
> Sent: 27 March 2022 10:15
> To: rob at jarratt.me.uk; Rob Jarratt <robert.jarratt at ntlworld.com>; General
> Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
> Subject: Re: PDP 11/24 - A Step Backwards
> On Sat, Mar 26, 2022 at 9:20 PM Rob Jarratt via cctalk <cctalk at classiccmp.org>
> wrote:
> > Can anyone suggest what else the CPU might need? Or is it LTC?
> >
> I would check the ACLO and DCLO signals. These are both high (pulled up by
> the bus terminator) for normal running, a PSU can pull them low if it detects
> loss of mains or whatever. Normally that will halt the CPU
> -tony

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