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SB16 CT2940 causes keyboard to stop responding

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First post, by TheMobRules

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Hi guys

I just installed a Creative SB16 CT2940 in one of my 486 builds and I'm having some strange issues. I first installed CTCM, it detected the card just fine and assigned all ports without conflicts. Then I installed the drivers and after everything was set up I ran DIAGNOSE.EXE to check if the card was working properly.

The port tests show no issues, but as soon as I perform any of the three sound tests (8-bit, 16-bit and MIDI) the keyboard stops responding and forces me to reset the PC in order to get it working again. Moreover, the digital sound for both 8-bit and 16-bit is kind of crackly and the MIDI randomly slows down the tempo of the test tune.

My first assumption was that this was a faulty card as I hadn't tested it since I salvaged it from an old Gateway a while ago. But I also have an identical CT2940 that is working fine on another PC, so I put it in the 486 but I get exactly the same problems with both cards. 😢

At this point I think it may be caused by some kind of resource/hardware conflict, but none of the system information tools I've tried report issues with the IRQs or DMAs, and other than the sound card the rest of the system is working without problems (it's a generic-looking Unichip 486 VLB motherboard with an Intel 486DX2-66, 256KB cache, 16MB of RAM, AVGA2 512K video card, Winbond I/O controller and Quantum Fireball 3.2Gb HDD).

If anyone has any suggestion of what could be the problem or other tests that I can try, I would be very grateful! 😀

Reply 1 of 2, by TheMobRules

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Just an update on this, as I seem to have found the cause of the problem: after doing some further testing I started getting "Internal stack overflow - System halted" errors and instability while running Doom. This led me to suspect memory issues, so I replaced the 16MB of 60ns Parity FPM (4 30-pin SIMMs of 4MB each) with 4MB of 70ns Non-Parity FPM (4 30-pin SIMMs of 1MB each).

That was it. As soon as I swapped the memory everything started working perfectly, no keyboard lockups, stack overflows or sound issues. Since I replaced the problematic RAM with slower memory, the errors shouldn't be caused by the RAM not being fast enough, and the motherboard supports parity modules (it's stated in the manual and there is a BIOS option for that), so all points to faulty module(s). The strange thing with this is that I never got any errors when using several tools that perform memory tests (such as SpeedSys or Cachechk), although these did report abnormally slow memory write speed, so maybe this is why.

Or maybe there is some option in the BIOS that I can tweak to be able to use these SIMMs without issues? The only DRAM related options I see are related to wait states... what would be a correct setting for a VLB system (33MHz bus) with 60ns RAM?

Reply 2 of 2, by Malvineous

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You shouldn't need wait states with *faster* RAM, they are used to make a quick system compatible with slow RAM.

Have you tried running Memtest86? I'm curious to see whether it identifies a fault with the known-bad RAM chip. Perhaps because it is parity memory it is able to correct most of the errors, which causes the strange irregular slowdowns?

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