Setting up a VAXstation

Tony Duell ard at
Mon Oct 8 17:28:22 CDT 2007

> The fact that PC kit is so cheap that it's not worth repairing is not
> why I don't repair classic machines. It's the reason I /don't know
> how/ to repair classic machines.

There's nothing to stop you learning how to do repairs on classics...

> > it. You mentioned swapping a DIMM. How can you know if an intermittant
> > memory problem is a fault in the DIMM or in the memory controller on th=
> e
> > motherboard?
> Well, although I realise that's just an example, I can respond using
> details of a recent real job.
> An AtlhonXP PC works fine with 2 DIMMs. With all 3 slot filled, it
> crashes, freezes or hangs. I suspect, from prior experience, a memory
> error. So step #1, I get a Linux boot CD with memtest86 on it, so I
> can exercise the RAM.
> With all 3 DIMMs fitted, memtest gives errors.
> With 2 fitted, it's OK.
> Try the 3rd on its own: fine.
> Try the other 2 on their own: fine.
> Try all 3 slots individually: fine.
> Summary: any permutation of 2 of the 3 is fine. All the DIMMs
> themselves check out fine, including on other machines. But on this
> machine, filling all 3 slots makes it unreliable. Given that I don't
> have a good motherboard to swap in, the resolution, then, is to
> downgrade it to 2 DIMMs & warn the owner not to try 3.
> That seems like a reasonable diagnostic process to me, and apart from
> fitting or removing the DIMMs, the only tests were done in software.


Oh %deity, where to begin...

OK, it works with 2 DIMMs, not 3. My first question is 'should it work 
with 3 DIMMs of that size'. Or is there a limit on the total memory 
that's been exceeded. 

Assuming there isn't, it would _appear_ the problem is with the memory 
controller on the motherboard. If it's some large ASIC that's failing, my 
expeirince is that when a chip starts to go bad, it gets worse. So the 
machine might have more mrmory errors shortly. I'd want to be sure any 
machine I'd fixed was working, and would carry on working. Not fail on me 
when I need it most

And I said 'appear' above. Maybe the motherboard is fine. Maybe it's a 
marginal PSU that can't supply enough current for the 3 DIMMs. Did you 
even chack the PSU votlages under load? Let alone ripple?

Now perhaps you know why I do all diagnosis and repairs of _everything_ I 
own myself...


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