help needed: problem with UNIBUS access on my PDP-11/70

From: Gooijen H <GOOI_at_oce.nl>
Date: Wed Jul 17 02:08:00 2002

The results of the last tests.
I measured the contacts on the G7273: all ok.
Next test.
Conditions: console in slot 40, G7273 in slot 41, M9302 in last slot.
            slots 42 till last also have G7273's.
Result: hung.

I swapped (sorry Tony) the G7273 of slot 42 and slot 41. Again: hung.
Last test.
Moved G7273 from slot 41 back into slot 42 and put the RX211 in #41.
The machine runs fine. PROMs on M9312, console, CPU regs, all are
accessed without PAUSE going on.

> OK, it appears there are 3 possibilities to check out :
>
> 1) The G7273 card is faulty and/or not making proper contact,
> and is thus not actually completing the NPG chain.
>
> 2) The device _before_ this slot (possibly the arbiter
> itself) can drive the input of the RX211 card, but can't drive the
> terminator. I have no idea if the latter is a significantly heavier
> load, but it might be!.
>
> 3) There is a problem before this slot (fault on the arbiter),
> which is genuinely asserting a grant signal, but the RX211 is
> getting into a state where it doesn't pass on grants, so said
> errant grant never gets to the M8302 to cause problems.
>
> Yet again I have to ask you to stop swapping cards around
> essentially at random, and to get out the test gear and make some
> measurements. With the G7273 card in, look at the grant lines at
> the teminator. Is one high? which one? Is it genuinely high, or
> marginal? What are the grant lines doing at the arbiter? All low
> as they should be? Can you get continuity along the grant chain
> with just G7273 cards in the machine? If not, why not? And so on.
> Actually get some evidence before trying to cure the fault.
>
> -tony

Well, I am not swapping at random, but at this point the simple tests
are exhausted. With the tests/swapping I established good starting
points where to look. I agree it is time to pull out the "heavier"
tools. This means more than just a quick glance at the schematics.
I will post those results, but that might take a while ...

tnx all,

- Henk.
Received on Wed Jul 17 2002 - 02:08:00 BST