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Anyone in the US have a Microvax?

S

shirsch

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Joined
Aug 17, 2008
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870
Location
Burlington, VT
Anyone here have a Microvax that uses those oddball T-shaped SIMMs? I have an issue with chronic fails on my Microvax 3100-96 during power-on test. Swapped SIMMs around a bit and unfortunately the problem doesn't move - except sometimes when it does. Starting to wonder if all four are defective. Before spending big-bucks on new memory I'd like to send these to someone in the US with a compatible machine to see if they operate properly on a different motherboard. Would be glad to pay for round-trip shipping.

It's going to break my heart if the motherboard is bad. This machine is in pristine condition otherwise. If you can help, or know someone who can, it would be greatly appreciated!
 
I have several microVAXen (and a couple megaVAXen), but none that use SIMMs. There are a few options available on ebay that aren't too expensive ($45 for a pair) you could try. I don't know the compatibility matrix, but I would expect an MS44L-BA to work.

CW
 
Try spraying the SIMM connectors and the sockets with DeOxit D5 contact cleaner. Lately when I pull a QBus board and later try to reseat it, about one time in four it, it doesn’t work. When that happens I blow the slot out with compressed air to make sure there is no lint/dust in the slot then spray both the board and slot with DeOxit, wipe off the excess and reseat it. It is amazing how many times that has fixed things. The best part is that it is really easy, so try the easy stuff first.

Mark
 
I saw those 16MB SIMMs, but they must install in groups of (4) and that starts to get a bit pricey for a throw of the dice.

I fully agree on the importance of DeOxit and cleaning. Unfortunately I've been through all of the sockets and SIMMs twice with no improvement. Need to decide how lucky I feel before buying any SIMMs. If the motherboard is flaky I have no other systems I can use them in - an expensive diagnosis. That's why I'd like to send them to someone with a known working box.
 
I have a 3100 85 (I think it's been years since I used it) with 128MB of RAM from what I remember.
 
According to the docs that uses the same memory modules. If the system is still operational would you mind trying my SIMMs in it?
 
I have some of those and a few bad SIMMs, but system having issues with all might have issues with the power supply, Check for stable power before you continue. Did you remove the battery?
 
The original NiCad battery had a minor leak and there was some green residue on the connector terminals and the top of the closest SIMM socket. I soaked that side of the board in vinegar overnight, washed it with distilled water and dried thoroughly. After checking with a magnifier I could not see any digested traces or vias. I had installed new battery before doing any power-on testing.

I'm also a bit suspicious of the power supply, but unlike the earlier DEC gear I could not find any low-level technical information or schematics. Is there a document that I missed? I can certainly take a look with a scope to check for excessive ripple.
 
What error messages do you get and/or how far do you get into the power up test?

I;ve never seen a schematic of the 30-35042-01 power supply. There may be some limited detail from people who have reversed engineered it. Bad electrolytic capacitors are a common problem in gear of that era.

Jerry
 
Well, after making voltage and noise measurements on the power supply everything looks fine. Voltages spot-on and noise is < 20 mv P-P. Picked up (4) tested 4 MB memory modules and same error occurs during system check. With great reluctance I must conclude the system board is just plain NG. Found a tested 3100 M90 motherboard on eBay for $280. I'lll put that in the unit and move on.
 
shirsch said:
The original NiCad battery had a minor leak and there was some green residue on the connector terminals and the top of the closest SIMM socket. I soaked that side of the board in vinegar overnight, washed it with distilled water and dried thoroughly. After checking with a magnifier I could not see any digested traces or vias. I had installed new battery before doing any power-on testing.

I'm also a bit suspicious of the power supply, but unlike the earlier DEC gear I could not find any low-level technical information or schematics. Is there a document that I missed? I can certainly take a look with a scope to check for excessive ripple.
Click to expand...
What was the battery you used as a replacement?

I tore into my 3100/85 to see if my battery was leaking and it had green junk on the terminal, but the board looks clean). It's a Panasonic NRAA 12-19245-01 RCE 9410 but I don't seem to find it online.
 
Unknown_K said:
So 3.6V Mi-Nh? what about the mAh rating?
Click to expand...
3.6V 180mAh DEC 12-19245-01

There's a guy selling them on Ebay but they're not cheap. https://www.ebay.com/itm/302015244803

I tried building a pack from cells but had issues getting the wiring to work. Then I bought a 3.6V 450mAh pack on Amazon which worked fine but didn't fit into the holder. So I got the Ebay one. Made an offer but I think he only knocked a few bucks off. At least it snaps into the holder and I don't have to worry about it flailing about if I move the computer.

1705970791000.png1705970809219.png
 
 
I recommend to not replace it, leave it empty. I have seen to many battery packs leaking after month when not charged.
Sure, I assume none of you is running their machines frequently.

When I got a 4000-105A I saw that it had a lot of green on the mainboard. I could not find any damage but memory was not working at all. It was detected in all 8 slots, Bank 0 and 1. All with two ?? marks.
I then verified it in a 3100/80 and 4 of the modules where dead. I did place the 4 good ones in the slots for Bank 0 with no success, then in Bank 1 with same error.
There was a firmware upgrade in the early days of the 3100/96 and 4000/105 fixing some timing issues. Don think it is the case here.
One final try with the 4000-105A is to recap it in the memory section. Have not given up yet.
 
Schroeder said:
There was a firmware upgrade in the early days of the 3100/96 and 4000/105 fixing some timing issues. Don think it is the case here.
One final try with the 4000-105A is to recap it in the memory section. Have not given up yet.
Click to expand...
Was that firmware update ever publicly available? Do you have a link to it?
 
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