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NOTE: This Vdimm Mod is for Rev 1.X and 2.X boards only. The power supply circuit may be different on other Rev boards....
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 mods, I strongly suggest you do not implement them...
The Vdimm adjust in the BIOS, only allows 2.8Vdimm. As this is hardly enough for todays highest performance memory, here is a modification to increase the Vdimm voltage. The Vdimm can be measured at the lead I have labeled on this Inductor that has the reference designation "L6". The return or ground lead of the DMM, can go to any ground or the "shell" of the I/O connectors...
The Epox-9NDA3+ Vdimm power supply, uses a 1 phase step-down switching regulator for maximum efficiency. The PWM chip is a RT9202B It's a 8 pin IC and has the referance designation of "U7":
The Switching Regulator circuit is a typical, but state-of-the-art, Synchronous Rectifier, 1 phase circuit.
-------------------- Too Many Computers,... Too Little Time ..... Damn Phenoms! Posts: 24294 | From: Fire Island, NY | Registered: Feb 2003
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This is the chip that we are going to add a resistor to:
The resistor that will be added to increase the Vdimm, is to be connected from pin 6 to pin 3 which is ground. I placed a white dot next to pin 1. The pins are numbered counterclockwise...
I tested various resistors and here's what each yields:
What I do with very small parts like this is 1st, cut the leads and form them to where they go. I then "tin" the ends of the resistor and try to leave a little solder ball on the ends...
Then I hold the resistor in place while heating the resistor lead until it flows to the IC lead...
Be aware that the IC can be easly damaged with too much heat... If it takes more then 5 to 10 seconds, stop and try after a while...
I have an old circular, floresent desk lamp that has a large magnifing glass in it. I'd be lost without it....
Great job!!!
-------------------- Too Many Computers,... Too Little Time ..... Damn Phenoms! Posts: 24294 | From: Fire Island, NY | Registered: Feb 2003
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Bypolar, when you say you couldn't use the Pomona Grabbers for the mod on that 8-pin chip, you mean they will work it's just that you didn't try it?
Posts: 234 | From: Japan | Registered: Dec 2004
quote:Bypolar, when you say you couldn't use the Pomona Grabbers for the mod on that 8-pin chip, you mean they will work it's just that you didn't try it?
The grabbers I have from Radio shack where to large to fit on the pins.
Maybe some Original grabbers would do the trick.
-------------------- In constant change!! Posts: 1715 | From: US | Registered: Jun 2003
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I have the original grabbers and they should fit; I know they fit the legs of darn near any chip. I guess the VDIMM mod is similar to the P4C800-D.
BTW, what version board are you using ByPolar? Rev. 2.x?
Posts: 234 | From: Japan | Registered: Dec 2004
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It's time to get a little more sophisticated and provide a way of adjusting the Vdimm.
What we're going to do is put a 3K resistor in series with a 20K, 10 turn pot. That gives us a minimum Vdimm increase of +0.1V. The maximun could be over 3.3Volts... One must be careful with running higher voltages on any component, and some active cooling is preferred...
Here is a picture of what to do with a 20K pot. You need to get a 3K resistor also... The 3K resistor provides a "stop" so that the Vdimm regulator doesn't go to 5V out!
-------------------- Too Many Computers,... Too Little Time ..... Damn Phenoms! Posts: 24294 | From: Fire Island, NY | Registered: Feb 2003
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I've set the adjustment to add +0.3V to the BIOS Vdimm setting. That way with the BIOS at 2.9V, memory is getting 3.1V. On the low end, with the BIOS set for 2.5V, I feed 2.8V to the memory... And I can always back all the way off on the pot and only add +0.1V to the BIOS setting.... Works nicely....
-------------------- Too Many Computers,... Too Little Time ..... Damn Phenoms! Posts: 24294 | From: Fire Island, NY | Registered: Feb 2003
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I have the pots with Pomona grabbers I used for the VDIMM mod on the P4C800-D, where I use a 10k pot. I tried and these grabbers fit this chip.
Now you say it's dangerous with the pot, but as long as I have the pot set all the way to the left (for me): maximum resistence, it's OK to use as long as I move up slowly and check VDIMM?
I want to get this straight so I don't fry the board.
But the S939 boards run BH-5 poorly, or any CAS2 ram for that matter. I'm wondering whether it's worth it. And does the VTT track 1/2 the VDIMM? Is anyone running BH-5 at 3.2 volts benching 3D OK?
Posts: 234 | From: Japan | Registered: Dec 2004
Damn Phenoms!
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10K gives me 0.18V The calculated value for +0.20V was 7.7K....
