PDP-11/70 debugging advice

Josh Dersch derschjo at gmail.com
Thu Feb 4 15:51:20 CST 2021

On Thu, Feb 4, 2021 at 10:19 AM Fritz Mueller via cctalk <
cctalk at classiccmp.org> wrote:

> > On Feb 3, 2021, at 8:07 PM, Josh Dersch <derschjo at gmail.com> wrote:
> > Sure enough, TIGB XTAL H was a flat line.  Nothing happening at the
> crystal itself either.  The crystal's casing was fairly corroded (which is
> interesting, since nothing else on the board is) and after a tiny bit of
> prodding one of the legs fell off, so I'm hoping that's the culprit.
> Ah.  One of the switches on the KM11 should enable the machine to run off
> the separate RC maintenance clock on the TIG, if you want to keep going
> before your new crystal shows up.

Yeah, you'd think... but it doesn't work :).  I mentioned earlier in this
thread that it's stuck in single-step mode.  From the schematics it looks
like the crystal clock needs to be running to clock some of the flip flops
used in the "Source Synchronizer" to select the proper clock source.  My
guess is that since the clock isn't running, the flip flops are left in a
weird state.

Or there's another problem here unrelated to the crystal clock.  I guess
I'll see in a day or so.

- Josh

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