Allo !

Some of you know that the VGA passthrough of most Voodoo cards is not quite perfect and one has definitely noticed that through the passthrough, higher resolutions are noticably softer or even outright blurry and image is a little bit dimmer too compared to direct connection to the host video card.

I hooked up an oscilloscope not so long ago to the input and output and I could see that about 0.1V was lost on the already low 0.7V video signal, which explains the dimming and loss of resolution and the cause is the CMOS switch used for video switching. It has fairly high On-resistance and while the cards connect two sections per signal in parallel the result is still far too high... but what if there was 2 more ...? And that is what lead me to the fix ~

The switch chip, PI5C3384QE(X) is still made and can easily be bought from Mouser and other places for very low cost and you'll need one piggybacked to the existing one on your card to provide good enough result. One could go overkill and add 3rd more but there's nothing really to be gained from there unless you try to pass 2048 x 1538 (or something higher 🤣) at high refresh rate through the Voodoo... 2 is enough for most uses cases 🤣

All of the photos of the process are found here : http://www.tmeeco.eu/BitShit/PCschit/VoodooFix/
I can only attach limited amount of photos to a post so only some of the important ones are shown here :

The general process consists of straightening the pins of the new chip, I have used a screwdriver against something hard to push the pins straight. You need all of the straightness possible because the pins barely reach the original chip even when maximally straightened.

You also want to tin up the pins of the new and old chip or you'll have hard time getting the two connected. Use as much flux as necessary and don't worry about solder bridges, they will contain enough solder to fill in all the cracks and make good connections.

DO NOT TRY THIS IF YOU HAVE NO FLUX AT HAND ! Stuff in your solder wire does not count, you will need a can or tube of some rosin paste or a syringe of no-clean flux or a flux pen. You're only gonna make your life very very hard without and most probably ruin a card in the process. Get some flux before proceeding or let someone else do it for you.

Once all the pins are tinned you'll line up the new chip on top of old and run the iron over the pins (when you have fluxed them up more). The solder in those bridges will drag with the iron and fill in all the gaps between the chip pins, making good connections. You can wick away excess solder with desoldering braid or simply get it transferred to the iron's tip and remove it that way. I generally do it without the braid as it can suck away too much solder and you must apply some more to get connectivity between the chips...

There's also a bonus feature possible, many cards have inductors and capacitors on the RGB lines to reduce EMI but they are tuned to low resolutions and will muck up the image slightly. Getting rid of the capacitors and bypassing the inductors will let you have cleanest possible signal :

Here's the mod done on a Voodoo2 :

Happy enhancing ~