You can't use just a multimeter to determine which input goes to what output.
just No.

Ok thanx for the great detailed explanations in that case. I will wait for my chip to arrive

The chip came today and I installed it, the resistance values look good and looks like my previous shorts are gone.

Turned on the system and unfortunately no video but I can hear the system booting.

Before I gave up I tried starting with vga direct into 2d card, started a 3dfx game and then manually plugged vga direct to 3dfx (as you guys gave me the idea) and to my suprise got picture.

I don't have anymore time today to try do a side by side comparison with my other working card but what do you guys think is most likely happening.

1. got a semi dud chip? What are the chances it doesn't switch 2d but is doing 3d? (low I would say)
2. Another component carrying the 2d signal to the switch chip burned out.
3. "insert here"

At this stage if I was really desperate I could ofcourse plug my 2d card and the 3dfx into a kvm switch and manually switch them.

Yes I did check the soldering on each leg and I went over it twice with a flat tip to make sure its all solid, no bridges etc

at this point I'd say fuck it and grab an Extron VSW 2VGA A off ebay

it handles the auto switching just like the factory passthrough would and gives much better bandwidth

maxtherabbit wrote on 2021-07-21, 14:51:

at this point I'd say fuck it and grab an Extron VSW 2VGA A off ebay

it handles the auto switching just like the factory passthrough would and gives much better bandwidth

+1 to that

I disagree with darry and maxtherabbit. You are so close, you can't stop now! You either fix it completely or you destroy it! 😁
Seriously, this looks like a fun project. Let's not forget that most of us are not really in it for the "gaming" part. 😀

Hey, at least the Monster is drawing stuff again! That's great news, it means that the output stuff and business end of the GPUs is probably working at least.
Did you check to make sure you didn't accidentally bridge any of those tiny pins together on the chip you replaced? Also look for traces that may have burnt out from the surge.

Actually there is merit to the Extron switch idea too. By not running your VGA output through the Voodoo you avoid the usual signal degradation on your 2D/VGA signal, though it is a bit less convenient to use. It's your call whether or not you want to 'fully' fix the device though.

There is another way to avoid the image quality degradation in the passthrough : Image quality fix for Voodoo1 and 2 cards

@bloodem
I am not against the idea of trying to get it working again, as a matter or principle, though the extra degree of effort and possible risk involved would not entice me to do so if I was the one experiencing the issue. I personally used a dual-input monitor (Viewsonic PT771) with my Voodoo 1 and later Voodoo 2 for most of the time period when those cards were current tech to avoid using the passthrough and would probably do the same today, even with a fully working card . Consequently, if I purchased a card with the issue OP currently has, I probably would not even notice it . Anyway, what to do next is definitely a matter of personal opinion .

@Tiido
That's an interesting solution . If the OP decides to try to fully fix the card (and hopefully succeeds), this would be a great next step .

Now looking back in hindsight should of ordered 2 chips, could of tried both and even soldered 1 on top if they both worked to improve the pass through.

This is a second 3d monster I have so not currently in use but yes my aim is to have a backup/collection that works 100%

I am very happy that it is alive, I guess it will be a little side project when I have time to poke around, I may also order another chip again.

At the moment I have compared resistance readings on the chip, vga in and vga out with the working card.

They are all consistant in the way that all ground pins are grounded and all other pins show a similar resistance, however the working card has a slightly lower resistance on all tested pins of about 0.100 ohm but constant. if it was about 0.30 ~0.50 I would say that is normal to vary accross different hardware but .100 seems like there is some phantom component that seems to be open. Visually everything looks ok so that is the hard part

The video DAC chip (the big PLCC chip next to VGA ports) is most probably damaged, it is a generic part and there are several compatibles that you can try to source and use.

Tiido wrote on 2021-07-22, 16:10:

The video DAC chip (the big PLCC chip next to VGA ports) is most probably damaged, it is a generic part and there are several compatibles that you can try to source and use.

huh? he said the image is good when connecting a monitor directly to the voodoo when it's activated

that would give the DAC a clean bill of health

Whoops, I missed that part... *blames the increasing heat 🤣*

The problem is certainly localized to the switch chip then.

Looks like ill be looking around for another chip ill get 2 this time.

Curious thing on my working monster the chip is S3L384Q i guess its the same function but different part number, perhaps ill try this chip

They are pin compatible.

If you are able to measure in place, you could measure voltage on pin 1 and pin 13 before and after you switch to 3D.
There should be a different voltage when in 2D and when in 3D, if so your current chip is probably broke.
if not, you'll have more damage to fix somewhere on the pcb.

weedeewee wrote on 2021-07-23, 06:59:

They are pin compatible. […]
Show full quote

They are pin compatible.

If you are able to measure in place, you could measure voltage on pin 1 and pin 13 before and after you switch to 3D.
There should be a different voltage when in 2D and when in 3D, if so your current chip is probably broke.
if not, you'll have more damage to fix somewhere on the pcb.

Great tip, and I just had a good idea too. I will solder some long cables to pin 13 and 1 which will reach out of the case for easy measuring. Won't take place today tho, got a massive headache 🙁

edit: looking at the pinout those are bus switch enable pins, so in 1 state I am assuming there should be no voltage and in state 2 there should be voltage to signal the switch to 3d, am I interpreting it right?

without looking at the datasheet further, yeah, one state will low voltage, and the other state will be high voltage, where one state might be the 2D passthrough, and the other state being the 3D output.

Ok so I soldered two wires to pin 1 (BEA) and pin 13 (BEB)

starting the system with 3d monster connected with pass through cable I got no signal

BEA =5v
BEB = low voltage 188mv

let system boot change monitor to s3 virge, load up dos command for shadow warrior 3dfx, don't press enter yet

change monitor back to 3d monster and pass through cable to s3 virge
start game, same result

BEA = 5v
BEB = low voltage 188mv

have to physically turn off and on monitor and the game is working in 3d. Quit the game monitor back in no signal mode.

So I am getting the same readings the whole time

Bea - pin 1 is 5v this is the card facing pin so I am assuming the 5v is being sent to the chip here.

Beb pin 13 is always low voltage 188mv, this is the vga out facing side.

according to this table it is always in 3rd function on the function table

not sure how to interpret this, if the card wants to switch should it send low/high voltage to bea (pin1) to let it know what output to send to pass through or not?

So it looks like some other component responsible for sending low/high voltage to the chip is broken. I guess the clue is to try trace back pin 1 to the source

This is most likely bad news, I traced pin 1 going through 2 caps to the bottom big chip, pixelfx processor according to Google. It would make sense that the processor sends the voltage when it is time to switch. So it is partially fried 🙁

This is the pin that is directly connected to pin1 on the switch chip which is always on 5v. I couldn't find a pinout, does 1 exist? prob not. If it was one of the caps I guess it would either be shorted or open.

The good news? I see somebody on ebay is selling these chips, I have done a few qpfc chips before so I can do the job however not really looking forward to it or keen so undecided atm what to do. If my above diagnosis and thinking is correct

Edit: I checked on my working 3d monster and it seems that the pin on the pixelfx has about 1.3ohm resistance to the surrounding capacitors. On the faulty 3d monster that resistance is 0.030 enough to show continuity. However on both cards resistance from the capacitors to ground is ~. 400. So this most likely means there is some short inside the chip 🙁 not a external line where the caps are

This might be a dumb idea, but if all that is required for the switching to work is the proper logical level voltage on the switch pins depending if 3D is being used or not, would designing a simple "bodge circuit" that applies the proper logical level voltage based on the state of another signal pin that is always either high or low depending on whether 3D is in use or not be a possible alternative to chip replacement ?