VOGONS


First post, by fsmith2003

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Just curious what the issue may be? Have an older Tseng 4000AX card that works fine other than it has some subtle waves that constantly show up on the screen. Its mostly visible when in DOS and the white text shows these waves real well. When inside of a game or a graphical program it isn't as noticeable. It does not do this with another video card with the exact same system/monitor setup so I am almost sure it is the card but just not sure what? Just seeing if anyone had any pointers of what I may look into to fix this?

Reply 1 of 12, by Jepael

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Some cards have this issue.
What I think happens is that some ripple on power supply lines gets coupled to sensitive video circuits, such as DAC voltage reference.
The ripple might come from outside the video card (like power supply, another card nearby it, or hard drive etc) or from the card itself (DRAM chips consume current in large peaks).

Try moving the cards around in the motherboard slots or change power supply.
If the DRAM chips are socketed, try swapping another set of chips.
Otherwise, the only solution is to reverse engineer the card circuitry and put extra filtering near sensitive parts.

Reply 2 of 12, by fsmith2003

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Thanks I will check into those things. I have already switched around slots and even switched motherboards and still same result. I will switch power supplies and check the chips tonight though.

Reply 3 of 12, by kixs

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What monitor do you use? I find this usually shows on LCDs, while I haven't notice this on any CRT.

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Reply 4 of 12, by fsmith2003

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kixs wrote:

What monitor do you use? I find this usually shows on LCDs, while I haven't notice this on any CRT.

It is an old Gateway 17" CRT monitor. Hasn't given me any other problems with other cards to this point.

Reply 5 of 12, by kixs

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Interesting... have you tried with any other monitor?

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Reply 6 of 12, by fsmith2003

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I did try another monitor and power supply. Same result. It is definitely something going on with the VGA card. I don't know if its a capacitor problem maybe?

Reply 7 of 12, by Tiido

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Putting a 100µF+ capacitor on the power pins closest to RGB out on the RAMDAC chip usually fixes such problems.

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜

Reply 8 of 12, by retrocanada76

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could it be the cable as well ? Is it a shielded cable ? try making a loop with it.

Reply 9 of 12, by fsmith2003

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Tiido wrote:

Putting a 100µF+ capacitor on the power pins closest to RGB out on the RAMDAC chip usually fixes such problems.

Here is my card. Where would I be looking to try this fix?

The attachment 96C1C38E-8D73-4F1C-9DC8-7DC6E171D1AE.jpeg is no longer available

Reply 10 of 12, by fsmith2003

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retrocanada76 wrote:

could it be the cable as well ? Is it a shielded cable ? try making a loop with it.

Tried a few cables with same results. Thanks for suggestion though.

Reply 11 of 12, by Tiido

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fsmith2003 wrote:

Here is my card. Where would I be looking to try this fix?
*snip*

One of the 3 larger chips next to the VGA port is RAMDAC, the photo is too blurry to make out any details on the markings. You'll want to identify the RAMDAC, then look up its datasheet and then you can see the pinout and identify the critical pins that supply power to the RGB DACs. Sticking a large capacitor across them usually fixes any problems in the output.

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜

Reply 12 of 12, by holoprox

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I have the same problem here, obtained the smallest VGA card ever seen [158/40 mm board]

They never soldered C17, C18,RP1, R5.
Seams R5 and C17 are used when using the other type of ram?
C16 is only 10 mF @25V...
NO ferrites in sight?

https://youtu.be/PJRhZXRb7eA

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