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Don't blame the VGA cards.
Does the LCD work properly when connected to other computers (PCI, AGP, whatever) using your VGA cable?
If no: Either the LCD or the cable is broken.
If yes: Either the ISA machine's PSU is broken or a card sits next to the ISA VGA card that generates lots of electric noise, remove it.

Well, VGA is the only thing left to blame...
1) LCD and the cable are fine when connected to PCI/AGP/PCI-E cards.
2) the only other card in my test setup is the HDD controller. The cards are installed in opposite ISA slots which means there are 3 slots dividing them.

Edit: just tried a Trident 9000A and picture quality is a bit better but still not perfect.

Picture on a TVGA9000B:

Had a similar thing with a Voodoo 1. At 60Hz the apparent brightness of the image would vary slightly, in vertical strips. My other cards were fine at 60Hz. Running the LCD's auto-fit function helped but didn't eliminate the issue completely. At 75Hz everything was fine.

Gona's DOS compatibility matrix (http://gona.mactar.hu/DOS_TESTS/) mentions similar issues with certain cards, so this is definitely not unheard of.

I think thats related to the rather low end 50 or 66 MHz DIL DACs on the Trident cards.
From my experience 80 MHz and better DACs don't show these enhanced stripes, also the cards layout plays a role. There are as well cards with 40 to 66 MHz DACs that show a good quality image.
So the bad quality problem is definitely nothing you can extend to all ISA VGA cards. There are even ISA VGA cards with DACs up to 135 MHz with a brilliant quality. (Ti, ICS, AT&T, Bt, IBM Palette DAC and so on...)

Does your monitor have sampling phase adjustment, and does it have an effect of any kind, like shifting the bars horizontally? Does automatic adjustment help?

I took a look at some of the TVGA9000 cards, and simplest cards do not have DAC output anti-aliasing filters of any kind.
Analog monitors may not care or it may show signal undershoot or overshoot at pixel boundaries, but the TFT ADC will care depending on sampling phase. Some later TVGA 9000i models do have a place for filter components, but in some models they are mounted and in some models they are not mounted. So I *do* blame VGA cards in this case.

Based on the striping, the TFT samples the signal at its own frequency, as it most likely wants to scale the analog active portion to fit the screen, instead of sampling the signal based on VGA pixel clock and scaling the signal to fit the screen digitally. As most TFTs could lock to the signal and scale digitally, phase adjustment should work. So it might be that the display does not support 70Hz VGA signal, or it is optimized to 720x400@70Hz VGA text mode rather than 320x200@70Hz VGA graphics mode, as they should have almost identical timing (except for pixel clock and the fact that graphics mode is double-scanned to 400 lines, but the TFT cannot distinguish this).

I get the same blocking "effect" with these ISA cards: Trident 8900D, Tseng ET4000AX and Cirrus Logic CR5422. On Cirrus Logic 5429 there is no problem. This is only tested on LCD display (LG MW228) - if I find the time I'll setup a CRT monitor.

I think the same problem is with my VLB Tseng ET4000/W32 (but I'm not 100% certain). There is no problem with other newer cards.

I can confirm that the picture blockiness is not visible on CRT monitors. Tried several problematic graphic cards and they all look very good.

I always kinda suspect the capacitors on my old videocards being near dead causing issues with the dac output strength

You should use a crt monitor with those cards, not an lcd. There are comparisons of picture quality on some sites. Back in the 90's lcd tech was still in its infancy and games of that era were designed just for crts.

Our "Reveal" brand CL-5426 ISA card looked like that when brand new, on the CRT we had back then. I assume it was a worse card than most, but apparently cards with horrible signal quality were out there.

I think LCDs can make this type of problem more visible though. I noticed this on a minimalist A/V mod on an Atari console once - it looked fine on a CRT but on an LCD the banding was terrible until the circuit was improved.

Most likely the signal output is not "smooth" and the LCD responds to the inconsistency much more than a CRT does

Way back, I remember we were looking at ordering some 486 machines, and the one we liked (mostly) had a Trident card - which we asked if they could change, because several of the monitors we had just did not like Trident at all - CRT monitors, with a bad case of dot crawl with the Trident card - for an order that was going to be about a dozen, they were happy to fit a different stock card

Sorry for resurrecting an old topic. I recently purchased a used 486 desktop computer from a thrift store. It is a Zenith Z Select 100. It has a 486 DX 66 Mhz CPU, and I installed 32 MB RAM in it. I hooked it up to my 19" HP vs19e LCD monitor. It seems to work great, except when I am trying to run PC games. I also get vertical lines in games similar to the Wolfenstein 3d screenshot in this thread. I tried to install UNIVBE thinking that would fix it, but it didn't. The 486 has a Cirrus Logic CL-GD5428 with 2 MB RAM. My LCD monitor has clock phase adjustments and I tried all of them, but it doesn't seem to fix the problem. Is there a solution to this outside of purchasing a CRT monitor?

I was testing how much video card speed matters on a 33Mhz 486 pc some time ago. I was comparing a trident card and a tseng labs vlb card and the trident card had similar vertical lines on a lcd screen, but the tseng labs vlb card didn't have those.

Baoran wrote:

I was testing how much video card speed matters on a 33Mhz 486 pc some time ago. I was comparing a trident card and a tseng labs vlb card and the trident card had similar vertical lines on a lcd screen, but the tseng labs vlb card didn't have those.

This 486 has an integrated CL-GD5428 chipset with VGA on-board. I would need to buy an ISA video card or CRT monitor to fix it? I only paid $7 USD for this 486. It isn't worth it if I need to buy additional hardware.

Can you post a pic of this zenith pc u got? It seems like the one I had back then and I can't remember exactly how it looked 🤣
If it's the same then the 5428 would be an onboard vlb one - so no isa card would be faster thus making it a downgrade in reality...

keropi wrote:

Can you post a pic of this zenith pc u got? It seems like the one I had back then and I can't remember exactly how it looked 🤣
If it's the same then the 5428 would be an onboard vlb one - so no isa card would be faster thus making it a downgrade in reality...

Sorry for the poor quality of the pictures, my smartphone doesn't have a flash.

Yes that's it! A boring-looking box 🤣
Now I know what to look for, thanks for the pics!!!