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Causes for common VGA output artifacts?

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First post, by Ozzuneoj

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I've seen issues like these for years, but I'd like to finally get to the bottom of what causes these problems.

First off, what causes this kind of ghosting that moves around with whatever is on screen?

The attachment VGA_artifact1.jpg is no longer available

What component is usually responsible for this kind of problem? Specifically on something like a TNT2... but also, in general on other cards.

Next... this one is really tough to record, and even tougher to get it to survive the conversion process when uploading it online. If you sit back a bit, it is visible in this gif as a repeating horizontal wave going from left to right. On this particular card it is really only visible at 800x600. For some reason, the card works fine at 1600x1200 at 60Hz, with only very very subtle distortion at 1024x768 or 640x480. But at 800x600 it's really distracting. The appearance changes a bit with different refresh rates, but it doesn't go away. Sometimes it looks more random and scattered, but in this case it's pretty clearly going from left to right.

The attachment VGA_artifact2.gif is no longer available

What causes that?

Also, these were taken on a Dell 2001FP (obviously) using a standard VGA cable. The two artifacts were on different cards. The first was an AGP TNT2 M64, the second was on a PCI TNT2 M64. Other identical cards do not exhibit these problems, so these are defects with these particular cards.

I have also tried hitting the auto adjust button on my monitor and it doesn't make either of these go away.

(Pro tip: A large number of visual artifacts I've seen in DOS or in Windows seem to just be scaling issues with certain LCD monitors. If your display has an auto adjust or auto alignment button, there's a good chance it will clear up any visual problems your having, like swimming\shimmering text in DOS mode or strange dithered patterns in Windows.)

Now for some blitting from the back buffer.

Reply 1 of 27, by kixs

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I would also test these cards on another monitor and/or other VGA cable might be better/more compatible. But usually CRT monitor solves like 99.99% such problems.

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Reply 2 of 27, by Shagittarius

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Yeah make sure you have a shielded VGA cable, a good one, it makes a difference for me.

Reply 3 of 27, by Ozzuneoj

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Is the first one really a sign of a VGA cable issue? I've tested probably 30-40 cards on this particular monitor and cable in this exact location in this same computer over the last few months and I've only experienced this issue on maybe two or three cards and it does it at every resolution, in DOS and Windows.

With regard to the second one, I have two identical cards on hand and one has the wavy pattern, while the other doesn't. Seems odd that it would be caused by anything except for a defect on the card.

Now for some blitting from the back buffer.

Reply 4 of 27, by pancakepuppy

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Dark smearing across the screen: Saw this on a GeForce 256 and have heard from a few other people about their GF256s doing this as well. I'm not sure about the root cause, but I think it's DAC degradation. I experimented with fixing it by replacing the VGA connector and doing RGB signal buffering before it launches into the cable but neither approach helped even a little.

Ripples on the screen: In some cases you can get this from having really bad decoupling capacitors on a card. When it's just at one particular resolution and on an LCD, that might be a little funky synergy between the card's DAC and the monitor's sampling frequency/phase.

Reply 5 of 27, by BitWrangler

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Ozzuneoj wrote on 2023-02-17, 17:47:

Is the first one really a sign of a VGA cable issue? I've tested probably 30-40 cards on this particular monitor and cable in this exact location in this same computer over the last few months and I've only experienced this issue on maybe two or three cards and it does it at every resolution, in DOS and Windows.

With regard to the second one, I have two identical cards on hand and one has the wavy pattern, while the other doesn't. Seems odd that it would be caused by anything except for a defect on the card.

Well you could say the cable and card aren't matched. Either it is a signal integrity issue that the card didn't make enough attempt to avoid by a more paranoid design, or the cable is too good or just the right (wrong resonant) length resulting in a card that gives a robust signal making a lot of undamped reflections up and down the cable.

Edit: It could possibly be the case that the card bracket doesn't actually screw into the ground plane on the card, and the card is relying on backplate to chassis contact to provide the shield ground connection. If this is the case then a card plugged into a loose motherboard or not fully screwed into a case may exhibit this behaviour.

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Reply 6 of 27, by pentiumspeed

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Signal cable has no shielded wires for the RGB signals hence bad signal reflections. Change to quality cable and they will be thicker too.

Believe me, seen this before. At one shop I worked for once, a owner used a cheap extension VGA cable, told him to change it to quality cable as described and this noise disappeared.

Cheers,

Great Northern aka Canada.

Reply 7 of 27, by Ozzuneoj

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pancakepuppy wrote on 2023-02-17, 18:26:

Dark smearing across the screen: Saw this on a GeForce 256 and have heard from a few other people about their GF256s doing this as well. I'm not sure about the root cause, but I think it's DAC degradation. I experimented with fixing it by replacing the VGA connector and doing RGB signal buffering before it launches into the cable but neither approach helped even a little.

Ripples on the screen: In some cases you can get this from having really bad decoupling capacitors on a card. When it's just at one particular resolution and on an LCD, that might be a little funky synergy between the card's DAC and the monitor's sampling frequency/phase.

Yes, for that first problem I was thinking along the lines of it being a DAC issue of some kind, but the specifics of that are beyond my expertise. I'm assuming that since the RAMDAC seems to be integrated into the TNT2 (and most other newer chips), it is basically game-over for this card, right? I can't see any way it would be fixable if the RAMDAC is failing for one reason or another.

Is there a possibility it is related to bad caps?

BitWrangler wrote on 2023-02-17, 19:19:
Ozzuneoj wrote on 2023-02-17, 17:47:

Is the first one really a sign of a VGA cable issue? I've tested probably 30-40 cards on this particular monitor and cable in this exact location in this same computer over the last few months and I've only experienced this issue on maybe two or three cards and it does it at every resolution, in DOS and Windows.

With regard to the second one, I have two identical cards on hand and one has the wavy pattern, while the other doesn't. Seems odd that it would be caused by anything except for a defect on the card.

Well you could say the cable and card aren't matched. Either it is a signal integrity issue that the card didn't make enough attempt to avoid by a more paranoid design, or the cable is too good or just the right (wrong resonant) length resulting in a card that gives a robust signal making a lot of undamped reflections up and down the cable.

Edit: It could possibly be the case that the card bracket doesn't actually screw into the ground plane on the card, and the card is relying on backplate to chassis contact to provide the shield ground connection. If this is the case then a card plugged into a loose motherboard or not fully screwed into a case may exhibit this behaviour.

Sounds logical to me. What part of the card would a manufacturer beef up to reduce the chances of this happening? Maybe whatever that is is either different or broken on the card exhibiting the issues. Still, I will try a different cable. I just don't want someone else to have an issue with this part if I move it along to a new owner at some point.

pentiumspeed wrote on 2023-02-17, 19:58:

Signal cable has no shielded wires for the RGB signals hence bad signal reflections. Change to quality cable and they will be thicker too.

Believe me, seen this before. At one shop I worked for once, a owner used a cheap extension VGA cable, told him to change it to quality cable as described and this noise disappeared.

Cheers,

Which noise are you talking about, the second one?

I will definitely try a thicker cable on my test bench.

Now for some blitting from the back buffer.

Reply 8 of 27, by Shagittarius

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Both of those screenshots look like unshielded cable artifacts to me. Make sure your cable has the ferrite cores on it too.

Reply 9 of 27, by pentiumspeed

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Ozzuneoj wrote on 2023-02-17, 20:38:
Yes, for that first problem I was thinking along the lines of it being a DAC issue of some kind, but the specifics of that are b […]
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pancakepuppy wrote on 2023-02-17, 18:26:

Dark smearing across the screen: Saw this on a GeForce 256 and have heard from a few other people about their GF256s doing this as well. I'm not sure about the root cause, but I think it's DAC degradation. I experimented with fixing it by replacing the VGA connector and doing RGB signal buffering before it launches into the cable but neither approach helped even a little.

Ripples on the screen: In some cases you can get this from having really bad decoupling capacitors on a card. When it's just at one particular resolution and on an LCD, that might be a little funky synergy between the card's DAC and the monitor's sampling frequency/phase.

Yes, for that first problem I was thinking along the lines of it being a DAC issue of some kind, but the specifics of that are beyond my expertise. I'm assuming that since the RAMDAC seems to be integrated into the TNT2 (and most other newer chips), it is basically game-over for this card, right? I can't see any way it would be fixable if the RAMDAC is failing for one reason or another.

Is there a possibility it is related to bad caps?

BitWrangler wrote on 2023-02-17, 19:19:
Ozzuneoj wrote on 2023-02-17, 17:47:

Is the first one really a sign of a VGA cable issue? I've tested probably 30-40 cards on this particular monitor and cable in this exact location in this same computer over the last few months and I've only experienced this issue on maybe two or three cards and it does it at every resolution, in DOS and Windows.

With regard to the second one, I have two identical cards on hand and one has the wavy pattern, while the other doesn't. Seems odd that it would be caused by anything except for a defect on the card.

Well you could say the cable and card aren't matched. Either it is a signal integrity issue that the card didn't make enough attempt to avoid by a more paranoid design, or the cable is too good or just the right (wrong resonant) length resulting in a card that gives a robust signal making a lot of undamped reflections up and down the cable.

Edit: It could possibly be the case that the card bracket doesn't actually screw into the ground plane on the card, and the card is relying on backplate to chassis contact to provide the shield ground connection. If this is the case then a card plugged into a loose motherboard or not fully screwed into a case may exhibit this behaviour.

Sounds logical to me. What part of the card would a manufacturer beef up to reduce the chances of this happening? Maybe whatever that is is either different or broken on the card exhibiting the issues. Still, I will try a different cable. I just don't want someone else to have an issue with this part if I move it along to a new owner at some point.

pentiumspeed wrote on 2023-02-17, 19:58:

Signal cable has no shielded wires for the RGB signals hence bad signal reflections. Change to quality cable and they will be thicker too.

Believe me, seen this before. At one shop I worked for once, a owner used a cheap extension VGA cable, told him to change it to quality cable as described and this noise disappeared.

Cheers,

Which noise are you talking about, the second one?

I will definitely try a thicker cable on my test bench.

These are the smearing from cheap cables. Get thick one they'll have shielded coaxes for RGB signals. I have seen this before, trust me. Not the video card themselves, I have not seen any that made the smearing ever even on cheap ones if using a quality cable.

Cheers,

Great Northern aka Canada.

Reply 10 of 27, by RandomStranger

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I've seen similar with my 8800GT when I used it with DVI>VGA adapter. Other cards with the same adapter didn't have the same issue.

sreq.png retrogamer-s.png

Reply 11 of 27, by Ozzuneoj

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Well, I'm sad to say that neither of these is caused by the cable or the monitor, but I wasn't really expecting it to be in this particular situation.

One card always has the smearing\ghosting as shown in the first image. The other card always has the wavy pattern at 800x600 and 1024x768. So far, I have tried:

3 VGA cables. One basic modern cable with a moderate wire gauge and small ferrites. One older but very heavy black cable with medium sized ferrites. One older but very heavy gray cable with blue ends and huge ferrites. All totally different types of cable, and all exhibit the same issues.

2 monitors. One Dell Ultrasharp 2001FP (4:3 1600x1200 IPS LCD). One HP N246V (24" 1920x1080 IPS). Tested both monitors with the same cables. Just swapping cables from one monitor to the other while the system is running so I could easily note any changes... but there were none, no matter what I do with the cables.

The Dell does allow me to adjust the pixel clock which causes the wavy pattern (second problem) to change a bit, but I get the same wavy pattern on the other monitor, so it isn't the monitor itself.

And, to reiterate, I'm only having one issue on one card and one issue on another card. Both are TNT2 M64. One is a PNY AGP card, the other is an nvidia OEM PCI card. I can test 50 other cards on this same setup and they won't do this. I don't really care about the M64 cards themselves really, but once in a great while I will see these one of these problems on other cards, and I made this thread hoping to figure out the cause.

I admittedly test a LOT of cards, so maybe this isn't that common, but I have experienced it on enough cards to want to know if it's fixable.

Now for some blitting from the back buffer.

Reply 12 of 27, by pentiumspeed

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Wow, not expecting that bad.

Any chance that you have photos of the cards of interest that caused smearing?

Cheers,

Great Northern aka Canada.

Reply 13 of 27, by bertrammatrix

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Ozzuneoj wrote on 2023-02-18, 01:05:
Well, I'm sad to say that neither of these is caused by the cable or the monitor, but I wasn't really expecting it to be in this […]
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Well, I'm sad to say that neither of these is caused by the cable or the monitor, but I wasn't really expecting it to be in this particular situation.

One card always has the smearing\ghosting as shown in the first image. The other card always has the wavy pattern at 800x600 and 1024x768. So far, I have tried:

3 VGA cables. One basic modern cable with a moderate wire gauge and small ferrites. One older but very heavy black cable with medium sized ferrites. One older but very heavy gray cable with blue ends and huge ferrites. All totally different types of cable, and all exhibit the same issues.

2 monitors. One Dell Ultrasharp 2001FP (4:3 1600x1200 IPS LCD). One HP N246V (24" 1920x1080 IPS). Tested both monitors with the same cables. Just swapping cables from one monitor to the other while the system is running so I could easily note any changes... but there were none, no matter what I do with the cables.

The Dell does allow me to adjust the pixel clock which causes the wavy pattern (second problem) to change a bit, but I get the same wavy pattern on the other monitor, so it isn't the monitor itself.

And, to reiterate, I'm only having one issue on one card and one issue on another card. Both are TNT2 M64. One is a PNY AGP card, the other is an nvidia OEM PCI card. I can test 50 other cards on this same setup and they won't do this. I don't really care about the M64 cards themselves really, but once in a great while I will see these one of these problems on other cards, and I made this thread hoping to figure out the cause.

I admittedly test a LOT of cards, so maybe this isn't that common, but I have experienced it on enough cards to want to know if it's fixable.

Did you ever make any progress on these? I recently got a pci version of this card with the same exact problem. Unfortunate as these are relatively scarce in pci. Not so horrible in game use but really annoying during just system use.

Reply 14 of 27, by BitWrangler

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There has been some problems with low pass filters on the VGA output of some cards, TNT thru GF2 and various randoms, I see it alluded to a lot some 5 years back, like everyone knew what write-up or investigation or fixit guide was referenced, and us types who know enough to be dangerous about electronics will just FAFO on our own stuff, but I can't find that reference or a good post that starts from basics on it.

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Reply 15 of 27, by smola

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The ghosting effect on 1st picture. To me it looks like degradation of dac output transistors/amplifiers on analog lines rgb signals. I had similar issue with old GF256. I eliminated all aspects on analog outputs on vga lines and finally I fixed it by switching card to digital dvi output. The semi-solution was a tiny hack on pcb to block ddc signals during power-on and restart - it was another issue. Original card was Elsa GLoria II-Pro AGP Pro (Compaq OEM).
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Reply 16 of 27, by danieljm

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I just recently got a Diamond V770 (TNT2) and I'm seeing the exact same issues. Problem persists across different monitors(CRT and LCD), cables, and motherboards, all of which work fine on everything else.

The attachment smear.jpeg is no longer available

My card doesn't have DVI as an option, so sadly a mod like that won't work here. I'm considering trying to bake it to see if that helps. Never tried it before though, but I might as well throw caution to the wind. 😀

Reply 17 of 27, by Ozzuneoj

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danieljm wrote on 2024-06-20, 18:15:

I just recently got a Diamond V770 (TNT2) and I'm seeing the exact same issues. Problem persists across different monitors(CRT and LCD), cables, and motherboards, all of which work fine on everything else.

smear.jpeg

My card doesn't have DVI as an option, so sadly a mod like that won't work here. I'm considering trying to bake it to see if that helps. Never tried it before though, but I might as well throw caution to the wind. 😀

I have considered taking a heat gun to the cards that have this problem... it is probably a lot safer than baking them. I do have a moderate success rate with baking computer parts though. I baked a Ti 4600 10-11 years ago and it brought it back around to working condition. Sometime after that I made an overly optimistic decision to try to fix my friend's Sony VAIO all-in-one system that was plagued with a bad Geforce 8400GT onboard. I believe this was the infamous "bump-gate" solder problem, so I figured it was worth a try. 100+ screws later I was able to bake the stupid motherboard for that thing, and it fixed the issue... for a few months, then it died again. Immense waste of time for a computer that was totally not worth fixing (Core2 Duo, 4GB DDR2 667, 8400GT... bleh). I just wanted to make my friend happy and I thought "hey, I've baked a single random video card from 2001... what do I have to lose by dismantling a nightmarishly complicated AIO system and then baking the motherboard in my oven?"

Stupid stupid stupid...

Anyway, if you do bake it, don't use an oven that anyone cooks food in. Hindsight (and common sense) tells me it wasn't a great idea to do that back when I first learned of such "tricks". We're all still alive, but it's also possible that residual circuit board chemicals are to blame every time I forget something or say something dumb. 🤣

Now for some blitting from the back buffer.

Reply 18 of 27, by danieljm

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Ozzuneoj wrote on 2024-06-20, 19:18:

I have considered taking a heat gun to the cards that have this problem... it is probably a lot safer than baking them. I do have a moderate success rate with baking computer parts though. I baked a Ti 4600 10-11 years ago and it brought it back around to working condition. Sometime after that I made an overly optimistic decision to try to fix my friend's Sony VAIO all-in-one system that was plagued with a bad Geforce 8400GT onboard. I believe this was the infamous "bump-gate" solder problem, so I figured it was worth a try. 100+ screws later I was able to bake the stupid motherboard for that thing, and it fixed the issue... for a few months, then it died again. Immense waste of time for a computer that was totally not worth fixing (Core2 Duo, 4GB DDR2 667, 8400GT... bleh). I just wanted to make my friend happy and I thought "hey, I've baked a single random video card from 2001... what do I have to lose by dismantling a nightmarishly complicated AIO system and then baking the motherboard in my oven?"

Stupid stupid stupid...

Anyway, if you do bake it, don't use an oven that anyone cooks food in. Hindsight (and common sense) tells me it wasn't a great idea to do that back when I first learned of such "tricks". We're all still alive, but it's also possible that residual circuit board chemicals are to blame every time I forget something or say something dumb. 🤣

Hmmmm, I'm already far too forgetful and say way too many dumb things. Maybe I'll rethink this plan. 😁

I've considered getting a hot air station in the past. I think I'll hold off until I'm ready to pull the trigger on that.

Reply 19 of 27, by iraito

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Let me add one common issues that plagues some of my PCs, it's those horizontal speckles, i think it's electrical noise bleeding from other cables or devices connected nearby but if anybody knows this specific issue i would appreciate it.

uRj9ajU.pngqZbxQbV.png
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