So as final confusion I thought id share my findings which could be helpful how exactly the switch process works:
So the main chip will send 2 voltages to the hex inverter on pin 13 A3 also connected to the switch chip pin 1 BEa. This in turn will send a inverted voltage from pin 12 O3 direct to the switch chip on pin 13BEb
So sending a low voltage to switch chip pin1 BEa will also invert a high voltage to pin 13BEb
this is the signal for 2d mode
36.8mv - > A3 (hex inverter) + direct BEa (switch chip)
This gives a output from O3 on the hex inverter of 4.47v sent to the switch chip on BEb
For 3d mode the main chip will send 5.06V to the hex inverter on A3 + direct to switch chip on BEa. Once again we have a inverted voltage of 150.8mv coming out of O3 to BEb
* These readings taken on the working card
Now my chip being stuck on 1.8~1.9V is a mystery why it still works in 3d mode.
I had a good idea, I got a dc regulated power supply so I decided to manually inject voltage to A3 on the hex inverter. I simply soldered a wire to A3 ran it to the dc power supply and ran a ground wire to the pc case.
Starting the pc all plugged to the 2d card I got the bios beeps of no video card. I flipped on my dc power supply sending .3v and after 1 or 2 seconds I got 2d picture. The theory holds up.
I started swarrior 3dfx in dos and got a black screen as the game loaded. Still in 2d mode. I started turning the dial on the voltage up around only 1.5V the switch to 3d took place.
Conclusion:
- The ranges seem to be pretty elastic as don't need the 5V to switch to 3d looks like 1 - 1.5V is the spot, must be why my card is always stuck on 3d giving me a constant 1.8v
- I noticed that sending the voltage to switch to 2d I could turn off my power supply and it would stay in 2d and show the correct voltages from the switch chip, perhaps in my case the main chip needs a jump start?
- looks like I was right that the main chip has a fault at sending the right voltage but other components on the same line were damaged too, hex inverter + switch chip
- My old hex inverter was showing very low resistance to ground on A3, which coincidentally is next to vcc, I didn't check or can't remember but 0.17 resistance to ground sounds like vcc so it was most likely internally shorted to vcc, which would explain why on my original readings I was getting 5v, same power the vcc of the hex inverter to power it.
- It would be not too hard to rig a switch connected to pin A3 on the hex inverter to send either a low or high voltage but for me this would ruin the appeal of this card like putting cheap spoilers on cars. The card works, comes with a catch but will be workable through a kvm switch if needed.