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3.3V and AGP

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kahuna0k

Registered
Joined
Mar 16, 2003
Hello,

I would like to know where is usually the AGP voltage taken from, it's taken from the 3.3V line? or from the 5V line? (or from the 12V line??) I know each mainboard has different approaches to the voltage regulation, but I suppose there is somekind of standard. I'm asking this because I'm planning to redo the 5V mod in order to use better wire and a far better connecting method. The new connector has 2 lines, so I'm thinking what to pump up besides the 5V line. I have a GeForce Ti4400 voltage modded and two XP2400+ @ 2256Mhz, 1.8V.

Best regards,

- german
 
Yeah AGP voltage comes from the 3.3V line...and the 5V line...

The 5V line is where the 3.3V line comes from and the 3.3V line is where the 1.5V line (AGP) comes from. I know the 3.3V line is where AGP Voltage comes from and I am pretty certain that the 3.3V line comes from the 5V line, perhaps someone can back me up on that if it is correct.

Redoing the 5V mod to multiple MOSFETS should help to regulate the 5V voltage, which will trickle down to the 3.3V line and the 1.5V line. Of course you have to make sure that you only use the proper MOSFETS as per Hoot's sticky.

Oh Yeah... Welcome to the Forums.
 
So what are the orange wires coming from the PSU into the ATX connector (that are at 3.3V) used for? Only memory?? uhmmm, it would be strange don't to take advantage of the PSU voltage regulators... anyway I'm not sure, maybe AGP comes from 5V.

- german
 
Evidently I was wrong, the 3.3V line does not come from the 5V line but the 1.5V AGP line does come from 3.3V line as I said.

If you are not experiencing any problems with your system then I don't see the need to add an extra 3.3V connector, adding an extra 5V connection will help to regulate the 5V line and in turn the Vcore though. Are you concerned that your volt modded card is not getting enough voltage?

The 3.3V line is used for the 1.5V AGP voltage, the 3.3V VIO (cpu input/output) and the 2.5V DDR RAM (3.3V for SDRAM) so it is some pretty important stuff but AFAIK having a 3.2V reading for the 3.3V line isn't all that bad, especially if it is only being measured from the motherboard's voltage monitor. You are not below that are you?
 
The best of all IF SOMEONE IN THIS FORUM CAN show us how to modify a PSU's voltage output, for examples; 3.30V lines = 3.43V, 5.00V lines = 5.15V, or something like that. This would be important discovery because a Power Supply is responsible for the source of voltage output.

So we don't have to hardcore modified our mobo and VGA to simulated higher voltage.
 
I did post a mod on how to raise your 5V but it only works on Enermax PSUs, my 5V line went from 4.757V at idle to 5.187V at idle and now my 5V line never drops below 5.08V. The 3.3V line is another story though, it is regulated so you would have to modify the regulating circuit which would likely be a little more complex.

If you want to see that mod check out the thread I started:
http://forum.oc-forums.com/vb/showthread.php?s=&threadid=177571
 
If you are not experiencing any problems with your system then I don't see the need to add an extra 3.3V connector, adding an extra 5V connection will help to regulate the 5V line and in turn the Vcore though. Are you concerned that your volt modded card is not getting enough voltage?

Well, I'm having random lockups under win2k (although the drivers and their interation with the Tyan Tiger S2460 could be the cause here) and lockups under heavy stress testing under linux when using the GeForce Ti4400, if I switch back to my old all good Matrox G400MAX no problem at all. So I suppose that the GeForce is not getting enough voltage or something similar ...

The 3.3V line is used for the 1.5V AGP voltage, the 3.3V VIO (cpu input/output) and the 2.5V DDR RAM (3.3V for SDRAM) so it is some pretty important stuff but AFAIK having a 3.2V reading for the 3.3V line isn't all that bad, especially if it is only being measured from the motherboard's voltage monitor. You are not below that are you?

Sincerely I don't trust I2C chips for monitoring voltages or temps, and I don't know where to check for the 3.3 voltage "on mainboard" so no much info, but the BIOS reports about 3.22V at bootup, when nothing is stressing the GeForce.

Best regards,

- german
 
There should be a MOSFET or two near your AGP port where you can measure the 3.3V line, if you post your motherboard's manufacturer and model I may be able to find pics of it but I am sure you can find it on your own. Depending on its placement you may not be able to get to it with your card in. Here is a pic of what it will look like and it should give you a rough idea of where it will be (its different in all motherboards). You will be able to test it on either the middle pin or the "back plate" in the picture.

mb04cl_b.jpg


If you haven't already you should read Hoot's sticky about measuring the 5V line as a guide.

Most motherboards have the option to raise your AGP voltage to 1.6V, 1.7V or 1.8V. You should try that if you haven't already. If you can't get to the MOSFET to measure the voltage then you might be able to measure the voltage on your card if you can find the smaller MOSFETs on your card, of course those should be 1.5V not 3.3V. I assume that only half of the MOSFETs will give you the actual line (3.3V or 1.5V) and the other half will be slightly lower then the actual line, just like with the 5V line but I am not sure about that.

Does your system still experience those problems even if the card is not overclocked? The problems you describe could be due to poor voltage or due to lack of cooling or even, as you said, driver incompatabilities but if you have tried different drivers for both your video card and motherboard chipset that seems less likely.

Post back and tell us how it goes.
 
I have a Tyan Tiger S2460 (dual AMD), the main problem is that I have modded most of the mosfets and I have attached a heatsick glued with artic thermal adhesive to hem, mainly because as I'm watercooling, there is little air flowing through the case, and even less over the mainboard, so those mosfets where going up to 70ºC under heavy load (now they idle a 35ºC and never pass 40ºC). The GeForce Ti4400 is also volt modded (following instructions in http://www.xbitlabs.com/articles/video/display/visiontek-gf4ti4400.html) and the core is running at ~1.9V and the memory at ~3.5V , anyway if I don't overclock it, it keep random rebooting, I'm leaving this weekend, but next monday I will install the GeForce again and check if that new Antec TruePower550 is up to its fame. :-D

- german
 
Are you watercooling the GF4 too? If not then you should probably look at the cooling for the card, try running it with the case open and a big fan blowing into the case or putting it next to an open window if it is cold out (still with the case open). If the problem goes away then you should get some better cooling on that card.

The only other way I can think of to measure the 3.3V line would be right where the ATX connector is, on the back of the motherboard, so you would have to take your motherboard out of the case and get it in a position so that you have access to the back of the board... that might not be very easy. You can use the ground in one of the molex connectors and find the solder points for the 3.3V line on the back of the motherboard. It could be dangerous though, the solder points are so close together you could short something trying to touch your volt meter to the solder point.

I found a picture of your board and the mosfet that I think is for the 3.3V line is right beside the AGP slot, it would be quite difficult to measure, even if it doesn't have a heatsink on it, with a video card in. You can measure it with no card in and the system powered on but that will only tell you how good the voltage is without the card. If you have a PCI video card you could put it in and go into the BIOS and look at the 3.3V line voltage and measure the actual voltage on the mosfet to see how accurate your board is at measuring it.

In the picture of your board it seems the 4 mosfets below the ATX connector are for the CPU on the right, the 4 mosfets above and to the left of the AGP slot are for the CPU on the left, the mosfet below the RAM slots is for the RAM, the mosfet above the battery is for the PCI slots and the mosfet to the right of the agp slot is for the AGP. the pic of your motherboard is here.

I assume that mosfet beside the AGP port should read 1.5V (since the 3.3V line is already regulated in the PSU) but I am not sure, so it may also read 3.3V.

Let us know how it all turns out when you get back.
 
"I am pretty certain that the 3.3V line comes from the 5V line, perhaps someone can back me up on that if it is correct."
In the Dell PSUs(the Britney Spears of PSUs), a buck converter inside the PSU steps down the 12v to 3.3v.
An old hybrid AT/ATX(AT case, ATX connector) PSU I took apart generated the 3.3v from the 5v.
So it depends on the PSU.
 
Well,

I'm back and I've installed the card again using the Antec TruePower 550 PSU, outstanding PSU, totally silent (even for an all-watercooled system) and voltage don't move from 4.99V and 3.29V whatever I run, but too bad .. the GeForce Ti4400 still doesn't work, keep crashing under linux and under windows, I don't know what to think, maybe it's broken ... I doubt it because I've extensively tested it under my brother box (Duron 800 + generic mainboard) without any problem, and maybe that it just doesn't work under the Tyan S2460, I've read in the Tyan FAQ for the mainboard and in 2cpu that other people are having problems with it too. I won't spend a second on it, I'm gonna sell it, with the "home-made" copper blocks for memory and core ... what a pity, hard work for nothing! I really hate when this happens.

Best regards,

- german

PS: Back to my old but really reliable Matrox G400 MAX.
 
I have mystery crashes before, and I thought it was too high MHz, but I doubt it. Overclocking a GF4 ti4200 to 300/565 sounds reasonable.

The problem actually heat on some IC & coils on video card PCB ( not GPU processor or Memory ). While running 3Dmarks, touch with your fingers several ICs on its PCB, you will find there are some components that are really hot.

In my case, the voltage generator / comparator IC ( a square black IC with 4 pins on the left and right, the size is 0.4mm x 0.6mm ) and the coil nearby them are really hot. You can add small heatsink with epoxy.

If this doesn't work, consider to re-format and re-install windows again.
 
Well, I have crashes even at default clock speed, so heat isn't the problem.

- german
 
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