VOGONS

Which PSU Rail do 1.5v AGP cards draw from? (Socket A Instability with AGP + PCI cards - PSU 5v Insufficient?)

Topic actions

First post, by justin1985

Posted on 
User metadata
Rank Member
Rank
Member

I've dug back out an ASRock SiS based Socket A based motherboard that was being dumped by a library, and have tried to get it set up as a Win98 box. The CPU in it is a Duron 1800, and currently has 768Mb DDR, DVD, floppy, and SATA SSD via a generic adapter (StarTech didn't work on this motherboard!). I thought it would be a good system to be home for a spare GeForce 4 Ti 4200 that I have, as well as a SoundBlaster Live!

However, I found that it runs stable with EITHER the GeForce OR the SB Live! But with both installed all kinds of weird crashes begin. The GeForce 4 Ti seems to run super hot itself. I got the same results with a Radeon 9250 LE (which runs a bit less hot). Particularly with the GeForce installed I noticed the PSU getting REALLY hot. So I'm thinking the instability is probably insufficient power (on the 5V rail) from the PSU?

The PSU is a BeQuiet! 300W SFX unit, which is specified for 20A on the 5V rail, and a maximum of 125w across 3.3V and 5V together. The compact case I'm using means I can only use SFX power supplies, and it seems impossible to find any for sale right now specified for more than 20A on the 5V rail - even modern ones rated upto 850W or more. It seems that if I wanted to find a PSU with more power on 5v, I'd also have to buy a case that takes a full-size ATX PSU ...

If I want to be able to use the GeForce 4 in this case with an SFX PSU, would it be likely to work if I changed to a motherboard with a 12v CPU power connection? (socket 754 or 775?)

Which PSU rail does an AGP card actually draw from? If I use a motherboard that has a 12V connector, is the AGP card still drawing from 5V (or 3.3V?)?

Reply 2 of 2, by justin1985

Posted on 
User metadata
Rank Member
Rank
Member
tehsiggi wrote on 2025-09-26, 20:05:

If you want to see where cards pull their power from, I have measured it for a couple of cards, inclusing 9200s and a ti4200

https://tehsiggi.github.io/agp-power-monitor/

That's incredible - thank you so much for sharing this!

It seems interesting that the GeForce 4 Ti seems to split its power draw over all three rails more than many in your comparison. I looked up the AGP connector pin-out - with only 1 x 12v pin, that's quite load going through it! I suspect my issue is the fact the BeQuiet PSU lumps together the 3.3V and 5V rails with a shared limit.

I hope I've found another way around the issue - I stumbled across the fact this motherboard supports the Geode NX 1750, which has a quoted power consumption of 14w compared the 57w of the Duron 1800, and presumably similar ball-park performance. I managed to order one at a reasonable price, so hopefully that will be happier coexisting with both the GeForce and the SB live.

Go to top of page Go to top of page
Back to General Old Hardware
Close window
Close window