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486DX2 DOS PC works fine... until it's time to play games?

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First post, by wowbobwow

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Hi all!

I'm working on a neat old PC I (literally) pulled out of a dumpster a couple years ago. It's been in storage ever since, so this week I've pulled it out and started tinkering with it. Initially I found that it was super unstable, frequently refusing to even power on. Last night I replaced the BIOS battery and installed a new AT-style PSU, which immediately helped - now the machine powers up without issue every time, thankfully. I've also installed a fresh copy of DOS 6.22 onto a CF card via an IDE adapter. Here's a quick rundown of the current specs:

  • CPU: 486DX2 "S" running at 66MHz
  • RAM: 16MB
  • 8GB CF card in a CF-to-IDE adapter
  • Video: Diamond Stealth64 VLB
  • Sound Blaster 16
  • Floppy, GoTek, generic IDE CD-ROM drive, etc.

I ran some of the PhilsComputerLab benchmarks and got respectable scores, including 40FPS in "3DBench."

So here's the weird thing I'm struggling with currently: I'm able to boot the machine and use DOS apps and everything like that - it works fine. However, when I actually attempt to run most games or any of the more advanced benchmarks - basically anything with 3D elements - the system almost always hangs within a couple seconds. For example, this is my experience so far:

  • Doom (standalone or benchmark): installs and loads fine, freezes after 2-3 seconds of showing the game (you know the automated bit of gameplay that runs when the menu comes up)
  • Quake time-demo: same as above (loads, starts to play, crashes after 2-3 seconds)
  • Wolf3d: menu loads fine, I can set all my settings, but when I start the game, I get literally one frame of the game and the system hangs
  • WarCraft 2: intro movie plays fine, crashes immediately after the animated Blizzard logo

Visually everything looks good on my motherboard, my RAM passes all the tests I've tried, etc., none of the capacitors have leaked or are bulging, etc. Any idea what's going wrong here? Is there some sort of advanced or esoteric BIOS setting that might cause this behavior?

Co-founder of The Retro Roadshow, the San Francisco Bay Area's premier pop-up museum of vintage technology!

Reply 1 of 5, by Namrok

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How do the games do without sound? I'm guessing all the synthetic benchmarks that all ran perfect had no sound?

Win95/DOS 7.1 - P233 MMX (@2.5 x 100 FSB), Diamond Viper V330 AGP, SB16 CT2800
Win98 - K6-2+ 500, GF2 MX, SB AWE 64 CT4500, SBLive CT4780
Win98 - Pentium III 1000, GF2 GTS, SBLive CT4760
WinXP - Athlon 64 3200+, GF 7800 GS, Audigy 2 ZS

Reply 2 of 5, by wowbobwow

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Namrok wrote on 2024-09-13, 23:05:

How do the games do without sound? I'm guessing all the synthetic benchmarks that all ran perfect had no sound?

I've been getting the same behavior regardless of whether the Sound Blaster card is installed or not.

UPDATE: I've stripped the system down to the minimum functional config - removed the Sound Blaster, removed all the 30-pin ram (I left a pair of 72-pin sticks in there, they've both passed MemTest86 with no errors), moved the video card into a different slot, etc. None of that made any difference. However! I went into the BIOS and disabled both the Internal Cache and External Cache, and everything seems to work... but it's painfully slow. Re-enabling either or both caches causes the issues to crop up again. Not sure what to think here - any tips are very appreciated!

Co-founder of The Retro Roadshow, the San Francisco Bay Area's premier pop-up museum of vintage technology!

Reply 3 of 5, by Robbbert

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Some of those old machines had actual extra RAM chips to be the cache. It might pay to check them out or replace them. This cache is NOT on the usual RAM sticks.

Reply 4 of 5, by wowbobwow

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Update 2: I'm back with a cautiously optimistic update! I spent a couple hours of painstakingly tinkering with the cache timings for the external cache - rotating between 3-2-2-2, 3-1-1-1, 2-1-1-1, etc., I found that I was *almost* getting better results, but it was never consistent or reliable, and half the time it would totally break everything.

I took some pics of my full BIOS config, and just used the "Optimal" command to reset the BIOS back to whatever it thought was best... and I'm delighted to say that the whole machine is working like a champ now! Doom and my other games are running without issues, I'm not hanging at boot anymore, etc.

I'm going to start reinstalling my other ISA cards (Sound Blaster 16, Ethernet, etc.) and put the 30-pin RAM sticks back in (I'll only install one thing at a time!) and I'll continue testing, but for now I'm feeling pretty sure that *something* was screwy in the BIOS config that I just wasn't able to figure out on my own. Thank goodness for that "Optimal" option!

Co-founder of The Retro Roadshow, the San Francisco Bay Area's premier pop-up museum of vintage technology!

Reply 5 of 5, by Disruptor

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Can you post a picture of your processor please?

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