PDP-11/04 issues

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Thu Jul 29 19:14:12 2004

>
> I have a new-to-me 11/04 in the kitchen, and I'm having some very odd
> problems with it.
>
> Slot 1 - M7263 11/04 CPU
> Slot 2 - empty
> Slot 3, AB - M9301-YA
> Slot 3, c-F M7859 KY11-LB Console interface
> Slot 4, C-F M7856 SLU, switched for 9600bps, 8N1, 20mA C.L. console
> Slot 5-6 - G657/H228-B 64KW core assy.
> Slot 7-9, D - G727 grant continuity modules
> Slot 9, AB - M9302 Terminator
>
> In the "book" configuration, as above, it boots to zeroes on the
> console LEDs with the RUN light and SR DISP lit. I can CLR the SR DISP,
> but the only other response I get with the panel is by halting it
> (CNTRL-HALT), which lights the BUS ERR light.
>
> On the other hand, if I remove the M9302, the system powers up to
> 000002. I can load and examine addresses from the console, deposit

These are the clssic symptoms of an open-circuit grant chain (either BG
or NPG), or a fault in that area of the logic (maybe on one of the
cards). If a grant gets to the M9302, than that card asserts SACK to
unlock the bus. At which point the processor (or more precisely the
arbitor, but it's part of the processor board) attempts to remove the
grant and everything goes back to normal. The problem comes if the grant
didn't come from the arbitor in the first place (either due to a floating
signal to the terminator from an open-circuit grant chain, or from
defective logic on one of the boards) -- the arbitor can't remove the
grant, and the bus locks with SACK asserted.

I would start by checking the grant chain carefully, then seeing just
what the signasl at the terminator are doing, and then see what could be
causing whichever one to be asserted.

-tony
Received on Thu Jul 29 2004 - 19:14:12 BST