VOGONS

AGP 4x Pro Troubles

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First post, by LeCogular

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I have a ASUS A7N266-C Motherboard I'm looking to get working for a late era Win98 machine and am running into a weird issue with its AGP 4x Pro slot.

It works with a Creative 3D Blaster TNT2 Ultra, but not a 128mb version of the Geforce 4 Ti4200, despite both being AGP 4x capable and the latter being theoretically more befitting of that hardware as an early 2000s card to match the Mobo.

To be more specific, the red light underneath the AGP slot illuminates to indicate an incompatibility of some kind and the system refuses to power on bcz of an inbuilt protection in the Mobo to stop it powering on in such a state. I cannot gleam anymore information beyond this as the manual gives no specifics for why the light may illuminate outside of "The card won't work", and I cannot find any information regarding either the Mobo itself or AGP 4x Pro as a standard that might shed light on why the TNT2 Ultra works but the Geforce 4 doesn't.

Its not a power issue, or at the very least it should not be, as powering this is a Thermaltake TR2 RX 850W PSU, complete overkill for this machine I know but its one of the very few spare PSU's I have available that I can swap between machines, and I have no functional ATX 1.0 PSU's (I have one that needs repairs, waiting on time to sit down and figure out what magic smoke escaped).

I have tested both cards on 2 different systems, a ECS L7S7A2 which has 1.5v AGP 4x, and a Gateway I440BX which has 3.3V Universal, both of which can utilize both cards without issues related to the cards themselves.

I have no idea why the Geforce 4 does not want to work in this specific Mobo, does anyone have insight or theories as to why this might be the case?

Because I know someone will ask, here are the specific hardware parts
PSU: Thermaltake TR2 RX 850W
Mobo: ASUS A7N266-C
BIOS: Rev 1001.e
RAM: 2x 256MB DDR 133Mhz Infineon SDRAM (combined 512mb)
GPU that works: Creative 3D Blaster RIVA TNT2 Ultra 32mb (Part Number: CT6870)
GPU that doesn't work: EVGA Geforce 4 Ti4200 128mb (Part Number: 128-A4-NV78-S1)
Sound: Soundblaster Live! Value (Part Number: CT4670)

Reply 1 of 7, by shevalier

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Re: Video card works with AGP universal, but not with 2x or 8x
Take a look here, it seems to be your case.

Aopen MX3S, PIII-S Tualatin 1133, Radeon 9800Pro@XT BIOS, Audigy 4 SB0610
JetWay K8T8AS, Athlon DH-E6 3000+, Radeon HD2600Pro AGP, Audigy 2 Value SB0400
Gigabyte Ga-k8n51gmf, Turion64 ML-30@2.2GHz , Radeon X800GTO PL16, Diamond monster sound MX300

Reply 2 of 7, by LeCogular

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shevalier wrote on 2026-01-06, 10:04:

Re: Video card works with AGP universal, but not with 2x or 8x
Take a look here, it seems to be your case.

I understand the text descriptor but am having trouble contemplating the img attached with it.

From what I gathered, remove resistor C100 to allow the card to correctly utilize AGP 4x?

Reply 3 of 7, by PcBytes

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Pretty much. IIRC a lot of Ti4200s use the same type of PCB, and at least in the case of the Gainward Ti4200 64MB I have here, R100 is unpopulated. If yours is, just remove the resistor at R100.

"Enter at your own peril, past the bolted door..."
Main PC: i5 3470, GB B75M-D3H, 16GB RAM, 2x1TB
98SE : P3 650, Soyo SY-6BA+IV, 384MB RAM, 80GB

Reply 4 of 7, by LeCogular

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PcBytes wrote on 2026-01-06, 19:59:

Pretty much. IIRC a lot of Ti4200s use the same type of PCB, and at least in the case of the Gainward Ti4200 64MB I have here, R100 is unpopulated. If yours is, just remove the resistor at R100.

R100 or C100? Because I was referring to C100 in my reply to the above.

I also cannot find R100, where would it by chance be located on the PCB?

Reply 5 of 7, by PcBytes

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R100, and it's located on the back of the card, just on the edge of the AGP connector.
file.php?id=233836&mode=view
(photo from shevalier, but it seems to apply to most Ti4200 cards that use reference design.)

"Enter at your own peril, past the bolted door..."
Main PC: i5 3470, GB B75M-D3H, 16GB RAM, 2x1TB
98SE : P3 650, Soyo SY-6BA+IV, 384MB RAM, 80GB

Reply 6 of 7, by LeCogular

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PcBytes wrote on 2026-01-06, 22:47:
R100, and it's located on the back of the card, just on the edge of the AGP connector. https://www.vogons.org/download/file.php? […]
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R100, and it's located on the back of the card, just on the edge of the AGP connector.
file.php?id=233836&mode=view
(photo from shevalier, but it seems to apply to most Ti4200 cards that use reference design.)

Mine is indeed unpopulated, no resistor to be found at R100

Reply 7 of 7, by shevalier

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A2 (connection type) is located next to A1 (+12V).
If the video card is skewed in the slot, the +12V bus burns out.
Therefore, some manufacturers put a resistor there.
ATI put 2-3 ohms, which works.
Some manufacturers put 100+ ohms on nVidia chips, which could potentially cause problems with determining the AGP speed.
Some simply short connected the SMD resistor pads to a trace on the PCB.
This is also an acceptable solution.
In general, A2 should have very low (non-existent) resistance to ground for 4/8x mode or flow for 2X.
A3 must be grounded for 8X mode only (AGP_GC_8X_DET#) or flow for 2/4X.

Aopen MX3S, PIII-S Tualatin 1133, Radeon 9800Pro@XT BIOS, Audigy 4 SB0610
JetWay K8T8AS, Athlon DH-E6 3000+, Radeon HD2600Pro AGP, Audigy 2 Value SB0400
Gigabyte Ga-k8n51gmf, Turion64 ML-30@2.2GHz , Radeon X800GTO PL16, Diamond monster sound MX300

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