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Thread: 486 lock up issues

  1. #1

    Default 486 lock up issues

    So...been working on a 486 pure dos build for a while and finally got it ready to assemble...but ran into snag. The pc will lock up at random times (mid dos install, game booting, memmaker, sb card install etc. Even if it sits a bit too long, keyboard stops responding, but the cursor blinks like it ready.
    Any ideas what I'm missing? Ive rechecked jumpers tried 2 different vid cards (1mb western digital and 512k Trent), 2 diff io controllers (one standard hmc 16 bit isa and 1 goldstar vlb) tried no cache, 64k, 128k, 256k cache, all different ram config, jumper settings to adjust the cpu speed....nothing. Just randomly freezes with blinking cursor after the c prompt.

  2. #2
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    To possibly narrow it further. What version of DOS and what drivers/TSR's are running?
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  3. #3
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    Pull your cards and clean the contacts with an eraser then re-seat, but be careful not to jamb them back into the slots. Download and run "MEMTEST86" https://www.memtest86.com/download.htm
    If you have another AT power supply you may want to swap it just to eliminate a possible cause. Need more info on your setup; ie mobo type, RAM, CPU, DOS, etc.
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  4. #4

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    Just curious, but what speed of CPU are we talking about? Pretty much any 486 with a speed over 33Mhz needs at least a heatsink and anything above 66Mhz would likely benefit from a fan as well...

  5. #5

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    Quote Originally Posted by NeXT View Post
    To possibly narrow it further. What version of DOS and what drivers/TSR's are running?
    Dos 6.22, and currently...no other drivers or tsr. I had the supplemental floppy and the starter floppy from Phil's but eliminated them early on

  6. #6

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    Quote Originally Posted by Agent Orange View Post
    Pull your cards and clean the contacts with an eraser then re-seat, but be careful not to jamb them back into the slots. Download and run "MEMTEST86" https://www.memtest86.com/download.htm
    If you have another AT power supply you may want to swap it just to eliminate a possible cause. Need more info on your setup; ie mobo type, RAM, CPU, DOS, etc.
    Mobo is Lx400 a/p vlb, 8mb of parity ram, 486dx2 66mhz, dos 6.22.
    The psu is the only thing i havent tried yet. I have two others, but one im sketchy about since it popped a nreaker on the bench (there was nothing plugged into it, juat bare on counter but still)

  7. #7

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    Quote Originally Posted by T-R-A View Post
    Just curious, but what speed of CPU are we talking about? Pretty much any 486 with a speed over 33Mhz needs at least a heatsink and anything above 66Mhz would likely benefit from a fan as well...
    486dx2 66mhz. The board came with an 486sx2 50mhz, but the board supports the dx2 so I swap cpus and reset jumpers. I put a small heat sink but I did notice the cpu gets very hot to the touch even with heatsink

  8. #8
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    Quote Originally Posted by New2vtgpc View Post
    486dx2 66mhz. The board came with an 486sx2 50mhz, but the board supports the dx2 so I swap cpus and reset jumpers. I put a small heat sink but I did notice the cpu gets very hot to the touch even with heatsink
    Like T-R-A said, you should definitely at least be using a heatsink. In this case, having one will definitely help to increase the lifespan of the chip. If you want, you can also install a CPU fan.
    While I'm not certain this is the issue in your case, I've had computers that would lock up or shut down when the CPU overheats. Do you have any other boards to test the 486DX2-66 in, to see if the same thing happens? Does the board also lock up when using the original 486SX-50 chip?
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  9. #9

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    Quote Originally Posted by TH2002 View Post
    Like T-R-A said, you should definitely at least be using a heatsink. In this case, having one will definitely help to increase the lifespan of the chip. If you want, you can also install a CPU fan.
    While I'm not certain this is the issue in your case, I've had computers that would lock up or shut down when the CPU overheats. Do you have any other boards to test the 486DX2-66 in, to see if the same thing happens? Does the board also lock up when using the original 486SX-50 chip?
    Ya know....i never tested the sx ..ill try that next. I just swap psu and still does at random. But yea the dx2 even with heat sink feels super hot.. Like cant touch it hot. I'll test the sx2 and report back

  10. #10

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    Ok so update...and list of attempted fixes
    I removed all cards, cables, chips and jumpers. Cleaned edge connectors...cleaned and reseated bios, ram, cache chips...reset all jumpers. Tried 2 diff video cards, 2 diff io cards...3 cf cards, 2 cf2ide adapters, a 400mb hdd, and both a 486sx2 and 486dx2. Still did locked up at random...but now the lock up doesnt freeze pc, but makes keyboard not responsive...i noticed this durind jazz jackrabbit (the screen and music kept moving).
    Hard reset and same thing when it froze mid typing...so tried different keyboard but no change. Redid the edge connector cleaning and tried a ps/2 keyboard with 5pin din adapter, and redid bios settings....and havent locked up since.
    Was it my keyboard? I find it hard to believe 3 5pin at keyboars would all become nonrepsonsive mid typing...but so far so good. I'll try it again tomorrow night and see but its stable at the moment

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