Questions on a +3.3V PSU Mod have come up several times, so I prepared following mod description. The idea is to raise the +3.3V bus for the purpose of delivering a higher Vdimm to BH-5 or UTT memory modules. This of course, only works if the +3.3V bus has been previously connected to the Vdimm line on the Motherboard. The 3.3Vdimm mod will be outlined in sector for your Motherboard, if the board is capable of being modified. Not all can be modified.
The top sketch shows a typical PSU connected to a motherboard. The mod requires you to find the "Grey" "Remote Sense" lead for the +3.3V bus and install a series 100 Ohm resistor as shown in the lower sketch. The "Grey" "Remote Sense" lead is inserted in one of the "corner" pins on the PSU's ATX connector, along with a Orange +3.3V lead. It is usually Pin #tbd...
The Mod is to first cut the Gray sense wire, then connect a 100 Ohm resistor in series with that wire by connecting one end of the resistor to one of the Grey wires ends, and then connecting the other grey wire to the other resistor end. Do not remove the Orange & Grey wire from the ATX socket. After the 100 Ohm resistor is connected as shown, an adjustable 10K resistor and a series 1K resistor need to be connected across the "Remote Sense" lead and any one of the "Black" ground leads... The 1K resistor is to keep the adjustable resistor from causing a overvoltage shutdown, when it goes to 0 Ohms. The spec on the 3.3V is 5%, so adjusting the +3.3V to +3.465V will mean the 3.3V rail is still in spec. Any voltage higher then +3.465V, is a risk you must be prepared to take. The mod shown below, will be capable of approximatly a 10% increase of Vdimm, or 3.63V.
If you do this mod, your doing it at your own risk. The Rebels Haven Computer Forum will not be responsible for damaged systems or components... If your unsure about the mod, I strongly suggest you do not implement it...
-------------------- Too Many Computers,... Too Little Time ..... Com'on AM4! Posts: 26787 | From: Fire Island, NY | Registered: Feb 2003
posted
I don't know what you mean... Maybe the value?
I used 100 Ohm for the sense lead resistor, but it can be 91, 82, 75, etc. The actual value isn't important as long as it's between say, 50 and 150 Ohms...
-------------------- Too Many Computers,... Too Little Time ..... Com'on AM4! Posts: 26787 | From: Fire Island, NY | Registered: Feb 2003
posted
Damn i knew i should not have posted so hasty. OK here goes. We need as you point out a 1kΩ in series with 10k VR. If the psu 3.3 line will show difference between a low value of Χ(Ω) (shut down) and Y (Ω) (no difference in resulting voltage=3.3) what are X,Y equal to (or ~ equal). Also (thinking of the guarantee) after installing the mods does the sense wire need to be reinserted in the 20-pin conector ?
Posts: 10 | From: Greece | Registered: Nov 2005
posted
ΟΚ thanks for your answers i wouldn 't have asked any of them had i detected the problem with the trimmer. You see when i tested it alone the dmm showed the resistance variation properly. Anyhow, my little coclusion is that the voltage we see is depended on the load. With no load even 0 total resistance gave me no voltage boost. With a little 0,25 A fan 0 resistance meant 3,81 V and with a delta 1,5 A 9.2 fan it meant shut down. So gonna get me a couple of 2kΩ VRs . Also the sense wire doesn't seem to bother not being in contact with the 3.3 wire
Posts: 10 | From: Greece | Registered: Nov 2005
quote: Also the sense wire doesn't seem to bother not being in contact with the 3.3 wire
The sense wire and the orange lead from the cornor pin(with the mode resistors) must be inserted back into the ATX connector or the mod will not work correctly. From the above Mod decsription:
"The Mod is to first cut the Gray sense wire, then connect a 100 Ohm resistor in series with that wire by connecting one end of the resistor to one of the Grey wires ends, and then connecting the other grey wire to the other resistor end. Do not remove the Orange & Grey wire from the ATX socket."
-------------------- Too Many Computers,... Too Little Time ..... Com'on AM4! Posts: 26787 | From: Fire Island, NY | Registered: Feb 2003
Com'on AM4!
