M7264 Troubleshooting

Mister PDP vintagecomputersmn at gmail.com
Sun May 26 13:37:41 CDT 2019

On Sun, May 26, 2019 at 1:03 PM Brent Hilpert via cctalk <
cctalk at classiccmp.org> wrote:

> Didn't this start out with the RUN LED not lighting up?
> I don't recall it being mentioned that that was repaired.

I spent a good amount of time with the RUN LED issue, but eventually hit a
brick wall. I traced the signal from the halt switch all the way into the
"Control Chip" on the MCP-1600 chipset (All OK), but since the CPU directly
controls if the LED is on or not I was not able to determine why the CPU
was not telling the light to go on. Since other signals on the board were
looking good (as in it was trying to communicate with other cards on the
board), I am assuming that is a secondary issue.

On Sun, May 26, 2019 at 11:23 AM Jon Elson via cctalk <cctalk at classiccmp.org>

> > Well, if just ONE address line driver on the CPU has gone
> > bad (or a short in the backplane) it could prevent the DLV
> > from recognizing the address.  If there are any other
> > boards in the system, take them out.  Maybe even the
> > memory boards, and try to read/write the DLV addrsss from
> > the console.  (Oh, maybe that's the problem, you don't
> > have the full programmer's console on this machine.)
> >
> Oh, DLV means Q-bus, so there isn't much choice EXCEPT
> serial console, is there?
> Yeah, when the serial console doesn't work, you've got a
> problem. You could check each addr/data line to see that it
> wiggles.  If it doesn't wiggle, then you can see if the
> state it is in makes sense. Obviously, somewhere in the
> serial console routine, it should be addressing the serial
> console, so every line should at some point be in the state
> to select the console CSR.
> A logic analyzer set up to read out the bus would be a good
> tool at this point.
> Jon

 The only cards I have in my system right now is the M7264 CPU board, and
my M8043 DLV11-J (or M8017-AA, which I also have onhand) serial board in
the slot closest to the CPU. The M7264 has 4KW of memory onboard, but I
don't think the ODT prompt even needs any memory. I haven't gone and
checked if any of the lines are shorted when they are not suppose to be,
but a number of the pins are shorted with solder bridges on the back side
of the H11A backplane. They look like they have been there since this
machine was new, I am am assuming that they are intentional. When I get
home I will go and check to see if any of the data/addr lines are stuck
using my logic analyzer, as well as making sure those solder bridges are
where they are suppose to be.

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