M7264 Troubleshooting

Glen Slick glen.slick at gmail.com
Mon May 20 02:11:31 CDT 2019

On Sun, May 19, 2019 at 11:48 PM Brent Hilpert via cctalk
<cctalk at classiccmp.org> wrote:
> Except the SRUN (K8 SRUN L) action is not latched, so it probably appears as an
> active-low heartbeat pulse with some periodicity when the processor is in run mode.
> A low-going pulse during PH 3 every instruction cycle perhaps.


Page 171 of the PDF, Lights & Switches Board schematic

The SRUN L signal (routed from the backplane through the power supply)
is fed through a 74123  retriggerable monostable multivibrator
one-shot before driving the RUN LED. If the SRUN signal is a pulsing,
the LED might effectively be driven constantly on.

I don't have the H11 schematic. It's front panel might have similar
logic driving the RUN LED.

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