29 Jul
2004
29 Jul
'04
12:14 p.m.
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