EDIT: I solved the issue yesteday - it is a very special incompatibility - my UMC chipset + any sound card + faster VGA + CF card. I have removed the CF and used an old HDD instead and everything works fine.
I am still checking this interesting VGA card - but it is not a souirce od my issue. The CF card do somehow mess on the bus... Funny.
--
Just to explain:
It might be like that. Maybe there is simply a compatibility issue quite comon in those ancient times.
I have noticed a similar behavior on a 286 "TwinHead" based board in the past.
Now I am testing this board:
https://theretroweb.com/motherboards/s/powertech-mb459
I made it fully working (battery damaged, wrong cache chips, dirt) with one bug - distorted sound (music OK) in pure DOS Games (Prince, WOlf 3D..), surprisingly everything stable and ok in DOS4GW based DOOM and DOOM2. !!
Considered the fact doom is running in the protected mode and it is very demanding, pusing such a 486 setup to its limit, I highly doubt there is a HW problem. I was playing like an hour...😀
All benchmarks went ok too - speedsys, even memtest, CacheCHK etc...
This WDC and one older TVGA9000 (the one with the older square Trident DAC) are causing issues - and was afik doing the same at the above mentioned 286 board. (but both work elsewhere)
In both cases using a RealTek, or another ISA VGA solved all the issues.
No matter what you set in the bios - the issue was there even with disabled L1, L2 and BUS running 6,25Mhz (so pretty slow). Still the same. (Moving cards in the slots has no effect too)
Immediately after replacing the VGA - all GOOD.
I have been informed on the RetroWeb Discord that my assumption might be righ - cards are figting for some signal - such as IO CHRDY. (??)
Why I assume this:
- it needs to be something SoundCard needs extensively.
- it is glitching with all kinds of various sound cards
- it DOES NOT glitch in the Sound Card setup software - which is static and text mode only - all tests sound good
- HOWEVER if I play WOlf 3D my snd effects are distorted AND my graphics is glitching - visible "noise" at the edge where you see your ammo, lives etc. while the distorted sound plays. More movement. More glitiching.
I have seen the same with the above mentioned 286.
If I remember this 286 even worked with a later rev of TVGA9000 (internal DAC). I also know some TVGA9000 have turbo/normal jumpers somehow influencing the behavior towards bus.
- dont know if WDC is like that..(?)
For sure I can use a different VGA and I know this UMC chipset is senstive and the board is cheap ass thing - but still it is an interesting thing to study.
It might be an interesting issue for the other retro-freaks too 😀
maxtherabbit wrote on 2025-12-07, 23:06:
OK I'll try to get it out tomorrow. My recollection is that all the jumpers control video modes, and none would affect compatibility but I'll check
