I'd be looking at voltages.

1) What's "missing" between the slot types.
2) What generates the missing ones in the boards that don't work.

https://www.playtool.com/pages/agpcompat/agp.html

myne wrote on 2025-12-29, 05:16:

I'd be looking at voltages. […]
Show full quote

I'd be looking at voltages.

1) What's "missing" between the slot types.
2) What generates the missing ones in the boards that don't work.

https://www.playtool.com/pages/agpcompat/agp.html

Thanks, that’s an interesting link.

I have run into AGP cards that don’t display a picture on the AGP 3.3 board, but I’ve not run into a board that only works in text mode on the AGP 1.5 board.

I've tried a lot of cards in these three boards and most work fine if they fit the slot, including these two newer generation nvidia cards: Geforce FX 5200 ~Mar 2003 & Geforce 6600 ~Aug 2004 which is bonkers to me because that 6600 has an AGP - PCI Express Bridge.

Here are the cards that have had issues:

MSI Geforce 4200 NV25 ~ Feb 2002
-- Via MP3 boots but produces no video. Tried VGA and DVI outputs.
-- Intel 815 is fine
-- Nforce 2 boots, produces text most of the time, but graphics modes rarely produce a signal, and only for short periods. Tried VGA and DVI outputs.

TNT2 Diamond Viper v770 ~ March 1999
-- Via MP3 is fine
-- Intel 815 is fine
-- Nforce 2 won't boot

ATI All In Wonder 7500 ~ Aug 2001
-- Via MP3 - unstable in Windows under load
-- Intel 815 is fine
-- Nforce 2 won't boot

And of course, any PCI card that requires strong v3.3 is going to be problematic on the Via MP3 , since it only has the P* & P8 AT power connectors.

The problems with the NV25 remind me of when I was trying to get PCI cards newer than 1996 to work in an FIC VIP board and a Gateway BAT3 Anigma. Seems to boot OK, but there's no VGA signal. After a lot of fussing, I assumed that it was BIOS issue, not power related, because I had the auxiliary 3.3V power plugged into the Anigma board.

douglar wrote on 2025-12-30, 04:41:

myne wrote on 2025-12-29, 05:16:

I'd be looking at voltages. […]
Show full quote

I'd be looking at voltages.

1) What's "missing" between the slot types.
2) What generates the missing ones in the boards that don't work.

https://www.playtool.com/pages/agpcompat/agp.html

Thanks, that’s an interesting link.

I have run into AGP cards that don’t display a picture on the AGP 3.3 board, but I’ve not run into a board that only works in text mode on the AGP 1.5 board.

Only thing I can think of is some weird bios settings. IRQ, pallet snoop, memory hole, anything else plausibly related.
Oh, and force agp 2x just in case

Try updating/changing vBIOS on it.

OK, that sounds like a plan. But where to find a BIOS for a 180-10085-0000-A03 reference board?

This board has a BIOS posted and looks very similar: https://theretroweb.com/expansioncards/s/xfx-pv-t25a-naf8

It's also built on a 180-10085-0000-A03 reference board, but it is the Philips SAA7108E Digital video encoder.

That's just used for TV in, yes?

Check to see if the components near the rear plastic radiator mounting clip (c111, r110...) are broken.
When the radiator is removed carelessly, they are often damaged.
These components set the reference voltages for the AGP bus.

At the beginning of the AGP connector on the back of the PCB is a resistor called R100, indicating that the video card is requesting AGP 3.0.
On the you board, it's marked as 101 (100 ohms), although it should be 0 ohms.
This photo shows that in later versions, it was removed and simply connected to the PCB with a trace.
https://theretroweb.com/expansioncard/image/t … 07846960175.jpg

These look OK

You are saying R100 is better as a 0 instead of a 101 ?

douglar wrote on 2026-01-03, 20:14:

You are saying R100 is better as a 0 instead of a 101 ?

The AGP detection is implemented in a very strange way due to the need for compatibility with older versions.
This resistor theoretically shouldn't have any effect, because the signal is supposedly "digital."
But sometimes it does, because some motherboards use it as a "mechanical switch" for the analog voltage regulator circuits of the AGP i/o powering.

Although these signals (A2&3 andboth A66 and B66), which determine the reference voltage value for the AGP signals, were simply not used in AGP 2.x.
It's highly likely that your MVP3 is simply not getting enough current from the Linfinity +3.3V linear regulator (3 pin, big, near the AGP).
Switching to an ATX power supply, removing this regulator, and soldering wires from the 20-pin connector will help.

I have not made the resistor change yet, but I was testing a geforce 6200 in my nforce 2 board and grabbed the wrong card because they have the same cooler and the 4200ti worked! For like an hour! Several reboots. But then I put the 6200 in the system. And when I put the 4200ti back in, the system wouldn’t boot, no num lock.

Edit: And then a day later it is working again ..... Curious.