VaxStation 3100 memory problem

[thephysicist]

Hello

I recently acquired a VaxStation 3100 and have some issues with the memory. On boot the systems goes into a reset when doing the "B" test. After removing the 16 MB MS42-CA and only using the 4MB expander boot into console succeeds. I have now 2 questions:

a) booting without a 4MB expansion board completely fails - is that normal?
b) the MS42-CA board has 3 jumpers. Can anyone help me with some infos on those jumpers? I searched the internet up and down but nowhere was a description of those memory modules available

thanks
Michael

 

[DECtechGuy]

What are you getting on the console? Any errors? I've never encountered a VAX going into a reset on any kind of error, it usually halts. The VAXstation 3100 maintenance guide will be a decent resource if you haven't found it: https://vaxstuff.files.wordpress.com/2014/08/vaxstation-3100-maintenance-guide.pdf

The system should at least come up to console without any memory, since there's 4MB on the system board.

There will be nothing on the MS42-CA's jumpers unfortunately.

 

[thephysicist]

yes, I know it's very strange. The system does test B (memory), and suddenly starts all over again.
Is there maybe a termination plug in case there is no expansion memory?
The maintenance guide I already found (and about 20 other documents), but nowhere are the jumpers mentioned.

thanks
Michael

 

[DECtechGuy]

If you can get the system to a state where you are able to see the console prompt ( >>> ) run the memory tests described in the maintenance guide and see what you find. If no errors, how much memory do you find?

As for a termination plug, there isn't one described in any of the documents out there, some of which have parts lists that also have no listing of a terminator besides the ones for SCSI and the like. So I'd have to say that's a non-issue and not something you have to worry about being a possible problem.

Finally, I'd imagine the jumpers on the MS42-CA were never intended to be touched outside of engineering.

 

[thephysicist]

The problem is - if the card is in use, system does not reach the prompt. Instead after hanging for some time in Test B (memory), it resets.

Nevertheless I made some progress. The 3 jumpers marked (4MB, 8MB, 16MB) allow to selectively set the car to either 4, 8, 12 or 16 MB. 4,8 and 12 MB work, but the 16 MB setting fails. Unfortunately when selecting 12MB and additional 4MB card is not recognized or used - but at least I'm running now at 16 MB. The error that the system does not boot up at all without memo card is also gone - no idea why

thanks
Michael

 

[DECtechGuy]

Nice to find that the jumpers are marked, I'll have to check mine.

Just a wild guess, but perhaps a memory chip is probably bad on the board and causing a reset, which it shouldn't be doing so according to the documentation. So maybe a bigger fault, like a bad ground or voltage issue when testing 16MB? Would require a lot of electronics diagnosis.