PDP-11/34a hung bus problem.
ed at groenenberg.net
Sat May 14 13:23:59 CDT 2016
After being sitting dormant for 5 years in pieces, it was time
to reassemble my 11/34, but hit a problem (hung bus).
What has been done so far :
- removed all the cards from the backplane.
- vacuum the backplane.
- power up the BA11 and check the voltages.
-> LTC is ok.
-> ACLO & DCLO were 0V, replaced board in switch unit,
ACLO & DCLO now ok.
- measure voltage at back-plane with no cards, voltage reads 5.35 Volt,
trimmed them down to 5.15 Volt (no load).
- insert both CPU cards, KY11-LB card & bootstrap card, 5 full grant
cards, DL11-W and bus terminator card.
- power up the machine, voltages are 5.10 Volt, measured at the backplane.
- run light is off
- cntrl + boot shows register dump at printer.
- sending a character to the console via 777566 does print it.
All looks ok.
- power down machine, add memory (M7981, 128KW) in slot 4, replacing a
full grant card.
- power up machine -> run light is on, does not get cleared by
cntrl + halt.
- power down & replace memory with grand card -> run light is off.
- moving the memory card to slot 5 , 6, or 7 and fill the other slots
with full grant cards, -> run light does stay on.
- tried the same without the bus end termination card (as is suggested
in the processor manual), no effect :(
- tried a 2nd memory card (M8722, 128KW) in slot 4, 5, 6 or 7, no change.
- visual checking the backplane wiring did not reveal any oddity.
So what could be the problem here? The bus works without the memory,
but with it, it gets a hung bus, arghhh...
Any suggestion is welcome!
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