lexer98 - Sempron 3000+ (S754, Palermo) @ 2860MHz - 32sec 360ms SuperPi - 1M

[TheRealKiwi]

Nice done Mods, can you please describe how you made the vdimm mod? And how much voltage you can generate?

[ludek]

90% volt mods is to connect a resistor between FB pin (feedback) and ground. Sometimes there is a linear voltage regulator op-amp based, so you try whichever in- pin (there are 'in+', 'in-' and 'out' pins) to ground resistor. For example many socket A AsRock motherboards had LM358 as the part of NB voltage. Very often configuration is 3V3 rail -> mosfet (op-amp driven), so max VDIMM should be at least 3,1 Volt (resistance etc.).

[TheRealKiwi]

thanks for your very quick response!
I know feedback mods, i indentified the LM324 as vDimm Controller but was confused about the Datasheet because there is no FB-Pin, so thanks for your description.
I think i found a post of Lexer https://www.overclock.net/threads/the-socket-939-appreciation-club-and-knowledgebase-official.293448/page-1436#post-26399454

Am I right, that he used Pin 9 (Input 3-) to Pin 11 (GND)?
Just for understanding:
- Should it work to another GND-Point too?
- the other Input/Output curcuits (input 1/2/4) can be other voltages (vDD or something) or not used?
- if i modify that Input voltage to 5V instead of 3V3 Rail, can it work higher than 3,1V or i will fire it up? 3,0V is enough for my TCCD, only for research

[ludek]

Am I right, that he used Pin 9 (Input 3-) to Pin 11 (GND)?
~Looks like this, considering "ST" logo and the middle GND pin.

- Should it work to another GND-Point too?
~Yes, but the closest is best (there is sometimes GND, Power-GND, Analog GND, so to be shure I recommend to connect to 2cm/1inch "as close as possible")

- the other Input/Output curcuits (input 1/2/4) can be other voltages (vDD or something) or not used?
~yes, I remember AsRock had AGP, vDimmRef, vNB, vDimm on one quad-op amp like LM324, impressive

- if i modify that Input voltage to 5V instead of 3V3 Rail, can it work higher than 3,1V or i will fire it up? 3,0V is enough for my TCCD, only for research
~in this configuration almost always the power componnent is a power SMD transistor. If your mems eat 1Amp or 2 amps, and vMem is 2.5, from 3V3 rail, the power dissapated on transistor is 3.3-2.5 over 1 Amp is (I=U/R so 3.3-2.5 is 0.8 x 1 is 0.8 W, it's not huge, but if you run full load, the current might jump to few amps) So 1A from 3.3V is 0.8W and from 5V is 5-2.5 x 1 = 2.5 W. This makes huge power losses and hot transistor.

[TheRealKiwi]

i did this mod as seen in the picture (before you confirmed that) and works great, thanks!

On 9/28/2021 at 8:13 AM, ludek said:

yes, I remember AsRock had AGP, vDimmRef, vNB, vDimm on one quad-op amp like LM324, impressive

i asked because i only can go up to ~292Mhz BusSpeed, maybe need to try another CPU, because other guys get 320+ without vNB Mod.

On 9/28/2021 at 8:13 AM, ludek said:

in this configuration almost always the power componnent is a power SMD transistor. If your mems eat 1Amp or 2 amps, and vMem is 2.5, from 3V3 rail, the power dissapated on transistor is 3.3-2.5 over 1 Amp is (I=U/R so 3.3-2.5 is 0.8 x 1 is 0.8 W, it's not huge, but if you run full load, the current might jump to few amps) So 1A from 3.3V is 0.8W and from 5V is 5-2.5 x 1 = 2.5 W. This makes huge power losses and hot transistor.

mhh i think i dont get it fully.
the differenz from input and Output voltage multiply by Output current = power dissapated of transistor?
then for example, a RAM about 2,5V and 1A @Stock:
vDimm 2,5V/1A=2,5Ohm @5V Rail = (5V-2,5V)*1A = 2,5W dissipation as you wrote
but if i need 3.5V for same RAM Typ
vDimm 3,5V/2,5Ohm=1,4A @5V Rail = (5V-3,5V)*1,4A = 2,1W dissipation?

with higher Voltage and higher Current less dissipation, i think there is a mistake in calculation.

[ludek]

P=u*u/r or p=i*i*r, my mistake!

So its even worse because voltage diff is squared. Ehh electronic engineer doesnt remember ohms law... ?