VOGONS


First post, by seanneko

User metadata
Rank Newbie
Rank
Newbie

I recently replaced the motherboard in my 486 with a different model and have been having issues with it since. Everything was fully working before, and I didn't change any configuration.

Specs:

- Chicony CH-498B socket 3 motherboard
- Intel DX4 100
- 2x 16MB 72 pin FPM
- 1MB VLB ARK1000PV
- VLB I/O controller
- Sound Blaster Pro 2 CT2600

When digital sound is enabled in games, the computer will hang/reboot after a random amount of time, but usually no longer than a minute or so. When playing games with digital sound disabled, or games with Adlib only support, it seems to run indefinitely with no issues. I left Doom running overnight with sound disabled and it was still fine the next morning.

I've run memtest86+ overnight and it found no errors.

I changed the sound card settings to try different IRQ, DMA, etc. Made no difference. I don't believe there are any resource conflicts.

I formatted and installed Windows 98 out of interest to see if it behaved any differently to straight DOS 6.22, but it seemed to be exactly the same.

I'm pretty confident that the sound card is fine considering I never had any trouble on the old motherboard.

Has anyone seen anything like this before? I'm running out of ideas for things to try. Surely it's not a broken motherboard since it's 100% stable apart from this one problem.

Reply 1 of 10, by jesolo

User metadata
Rank l33t
Rank
l33t

What are the IRQ & DMA settings that you have tried?
Any other cards and/or devices in your system (not included in your list) that might also be using resources?

Reply 2 of 10, by seanneko

User metadata
Rank Newbie
Rank
Newbie

Currently set to port 220 IRQ 7 DMA 1, but have also tried port 240, IRQ 5 and DMA 0 (the parallel port was disabled on the IO card).

The current settings were what I previously used with success on the old motherboard.

No other devices in the computer. I did have an AWE64 too for MPU-401 support, but it does the same thing with that card removed.

Reply 3 of 10, by bjwil1991

User metadata
Rank l33t
Rank
l33t

Normally, port 220 uses IRQ 5 and DMA 1, otherwise certain games would think you have an Adlib installed and it won't produce sound effects. I'd also check the motherboard for capacitor issues, and the clock crystal as well (check to see if the speed is set accordingly in the BIOS for the ISA bus as well since older cards ran on certain bus speeds at 16MHz or equivalent) for any damage.

Discord: https://discord.gg/U5dJw7x
Systems from the Compaq Portable 1 to Ryzen 5 2600X
Twitch: https://twitch.tv/retropcuser

Reply 4 of 10, by jesolo

User metadata
Rank l33t
Rank
l33t

Some of these older sound cards tends to be speed sensitive on faster systems - try to slow down your system (if you have a turbo switch, use that or otherwise, try a utility like SetMul) and see how it performs then.
However, as I recall, from some tests that James-F performed, your Sound Blaster Pro 2 should run OK.

Another thing that came to mind is that you have the CT2600, which is the model that supports the Mitsumi CD-ROM interface.
That interface required additional IRQ's & DMA channels and these might be causing conflicts - if possible, disable everything related to the CD-ROM interface.

PS: What was your "old motherboard" (specifications)?

Reply 5 of 10, by seanneko

User metadata
Rank Newbie
Rank
Newbie

Hmm, I'm not sure if the CT2600 has any way to disable the CDROM interface. At least I can't see any jumpers to disable it. Would putting the card into an 8 bit ISA slot help in that regard? I recall reading that the audio all runs through the 8 bit part, and the 16 bit part is only used for the CDROM interface which I don't need.

I've tried running the CPU at slower speeds, in fact I even tried a completely different CPU (a DX2 66), but that didn't make any difference either.

The old motherboard was an ECS UM4980. The only reason I want to change it is because I prefer AMI BIOS, but the UM4980 has Phoenix BIOS. The memory tick sound really reminds me of my first computer, so AMI BIOS is a lot more nostalgic.

The ISA divider in the BIOS is set to 4 which should set it to 8.25MHz. Just for testing I also set it to the lowest which from memory was 6 (5.5MHz), but it didn't help the problem. Everything was noticeably slower though.

Interestingly, last night I swapped the sound card out to a different ISA slot (16 bit, haven't tried an 8 bit slot yet), then left Doom running with all sound enabled. This morning it was still running. It could just be a coincidence/luck I guess, but is this even a thing? Something works in one ISA slot, but not another? The board came out of an untested junk computer, so it could very well have physical damage. Maybe if I continue having trouble I'll need to look for damage on it.

Reply 8 of 10, by derSammler

User metadata
Rank l33t
Rank
l33t

Have you tried games other than Duke3D? I had exactly the same issue with Duke3D on a DX4/100 using a Formosa AudioStar-16. Using a different sound card fixed it. Other games did run fine, so I assume it's related to the sound code used by Duke3D, which may trigger some DMA bug with certain sound cards and/or on a DX4.

Reply 9 of 10, by asdf53

User metadata
Rank Newbie
Rank
Newbie
seanneko wrote on 2018-04-21, 01:16:

Yeah, spoke too soon. Tried a different game and it crashed pretty quickly.

Did you ever solve this? I'm having the same problem on my 486. I also tried different sound cards, different IRQ settings, PCI and ISA graphics cards, but nothing seems to help. The computer is stable otherwise, it only crashes when digital sound is played. One thing I noticed is that disabling the external cache in BIOS makes the problem go away. Does that work for you too? I wonder if this is a hardware problem or not. If it was a bad cache chip, wouldn't it crash all the time?

Here's an interesting discussion from 1995 about this problem: https://groups.google.com/g/comp.sys.ibm.pc.g … /m/k36DZbutYp0J
No solution there, but someone has also mentioned that disabling external cache made the problem go away.

Reply 10 of 10, by asdf53

User metadata
Rank Newbie
Rank
Newbie

I found the solution! I had noticed that the problem got progressively worse as I tightened the RAM timings in BIOS. Then I got a clue from the newsgroup discussion linked above:

I took my Soundblaster and tested it with a friends computer. It worked fine. I tried every expansion card. They all worked fine. I tested my SIMM's on his computer. They worked like a charm. I borrowed his SIMM's and plugged them into my computer, and Bingo. With his memory my computer worked perfectly. Apparantly for some reason the mother board didn't like my SIMM's. His' were 80ns and mine were 60ns.

I dug out another SIMM module with different memory chips, and sure enough, it works! No more crashes. I had tested the old memory with memtest and it didn't have any errors, it just seems to be incompatible with the motherboard and cache combination.

I also noticed that the non-working modules were both 8 MB, and the motherboard manual seems to specifically exclude 8 MB modules ("Each bank can accept either a 1 MB, 4 MB or 16 MB module"), so this could have been the reason why it wasn't working properly.