VOGONS

Memory problems with 128MB in 486-PIO2 motherboard

Topic actions

First post, by 8bitsten

Posted on 
User metadata
Rank Newbie
Rank
Newbie

Hello,

I have 4x32MB SIMM EDO 60ns from VisionTek (VT15214.6A modules with ICs TMS44100DJ) in motherboard 486-PIO2 with Award BIOS v4.50G (v1.022B101), where I have Intel 486DX4/100Mhz WB. Nothing else is here except of VGA card to see the output.

What I have done:

  1. I just set the motherboard jumpers, put it all together, and initially, all works, 128MB memory test always passed.
  2. After some time I noticed that instead of 128 MB the memory test stops at 112 MB like the one module would be only 16MB.
  3. I guess I identified the module and put back only three of them with 96MB in total.
  4. Again initially all work, but the memory test after some time starts stopping on 64MB only...
  5. Sometimes it wrote that the "Memory test failed".
  6. The reboot sometimes helps, sometimes not. Sometimes it works also with a full 128 MB, sometimes it even did not start...

I tend to believe that SIMM modules, CPU, and motherboard are OK as I bought them from trusted sellers. So I am trying to come up with what the possible problem could be? I am NOT an EXPERT. I am just putting together my child's dream computer...

My ideas of where the problem could be:
1/ General compatibility of SIMM modules and motherboard? Should I try other 32MB modules?
2/ Some jumpers on the motherboard?
2/ Do I need the BIOS upgrade?
3/ Should I try another power supply?

Observation, which could be wrong: With just two SIMM modules (i.e. 64MB RAM) it seems to be stable.

Thanks for any piece of advice
Petr

Reply 1 of 1, by mkarcher

Posted on 
User metadata
Rank l33t
Rank
l33t

Your symptom of the board slowly getting worse (it started out with supporting all 8 banks, then one of the banks failed, later only 4 banks could be used at the same time) sound a lot like a capacitor buffering the RAM power supply drying up over time. The three electrolytics near the RAM slots (CT15, CT18, CT19) thus are my primary suspects. If you happen to have a ESR meter, you can do a preliminary check in-circuit. A cheap "generic component tester" (the China type available on ebay for 10 to 20 bucks) can only test capacitors and show the ESR after desoldering. Desoldering these caps is likely more difficult than it looks, because they are connected to "power planes", solid areas of copper inside the board that distribute +5V and GND everywhere. These power planes suck away the heat needed for soldering like crazy, and you thus need a beefy enough soldering iron with a good clean tip.

You might want to try with a different AT power supply first before swapping caps on the mainboard, because replacing the supply is much less work than recapping the board.

Go to top of page Go to top of page
Back to General Old Hardware
Close window
Close window