VAXstation 4000/90 questions

[John Klos <john%ziaspace.com@localhost>]

Hi, VAX fans,

I'm now getting back to trying to get my 4000/90 completely happy and as 
stable as my 4000/60s. The memory issues have not reappeared after 
cleaning all of the SIMMs and SIMM slots with isopropanol. However, 
instead of memory soft errors on the serial console, I'm seeing hard 
lockups after a day or two.

The things I've checked are power (traded the power supply from a known 
good machine, plus it's on a good UPS), memory (swapped all of it with 
known good memory from my two 4000/60s), disk, battery backed clock chip, 
ethernet transceiver, and I've put a fan over the triac which is between 
the memory slots and the optical drive bay (which gets so hot without the 
fan it has burned my finger).

The system just locks. I have "options LEDS" compiled in the kernel, so 
it's easy to tell that it just stops. The serial console gives nothing and 
doesn't respond to a break. At least this is now unrelated to memory, or 
at least appears unrelated, since I'm not getting soft memory error 
messages on the serial console.

Since hardly anything else is modular and replaceable, the only other 
thing I could try was to remove the video card. I suppose I'll know after 
a day or two of compiling.

So here are my questions:

1) am I correct in assuming that there's NO software crash that could 
cause the system to hang and not drop to the boot ROM chevron prompt from 
a break?

2) has anyone seen issues like this with similar machines, and if so, was 
the root of the problem discovered?

3) does anyone have suggestions about anything else to check or try?

4) I think the only thing I haven't tried is replacing the heat sink 
compound on the CPU. Any thoughts on whether this could be an overheating 
CPU issue?

5) unrelated to the crashing, how does one tell the difference between a 
4000/90 and a 4000/90a? The casing doesn't seem to match the guts. Does 
someone have the specific results from a NetBSD benchmark on either a 
4000/90 or a 4000/90a, or both?

Thanks!

John Klos