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» The New Rebels Haven Forum!! » 32 Bit Motherboards and Processors » Shuttle 32 Bit Motherboards » The Vdd Mod For The AN35/N...

Author Topic: The Vdd Mod For The AN35/N... Polygon Admin Member # 1 posted                    With the Geil Memory Test I did today, I am starting to think that the FSB max of 260-270 I'm reaching, is due to the Chipset limitations.... As we know, the BIOS gives us no choices for Vdd and the default is 1.7Vdd. 1.7Vdd may not be sufficient for stable operation at 270FSB and above... Be aware that on the Jetway, which is very similar to the Shuttle, the changing Vdd from 1.7V to 2.0V didn't seem to make any difference.... But ignoring that, we forge ahead... The typical Switching Regulator Power Supply schematic for the RT9203 chip that is used to generate Vdd, looks like: The Chip that is the focus of our attention is circled in this photo and carries the reference designation "U20". Also in the photo is shown where to measure Vdd. The negative of the DMM can be returned to any convient ground, including the case. While the "Typical Schematic" above shows a 200 ohm resistor from pin 8 to ground, the DMM indicates the impedance is 51 ohms... The value code on the resistor is "93X", which is 90.0 ohms(?). The value of this resistor tells us what value to put in parallel. If the resistor is 200 ohms, a 2K resistor in parallel will increase the Vdd by 10%, a 1K resistor in parallel will increase the Vdd by approximatly 20%.... Not being sure what the circuit really looks like, I'll start with 10K and continue to reduce the value until I feel comfortable that I know what boards value really is in the circuit... The resistor needs to be connected between U20 pin 8 and U20 pin 3. Pin 3 is the ground, so any local ground should be fine, but due to noise pickup, the closer to U20, the better... Here's where the resistor goes: More as I test further... Posts: 25194 | From: Fire Island, NY | Registered: Feb 2003 Polygon Admin Member # 1 posted                    I reduced the parallel resistor all the way to 1K before I got some significant change... 1K increased the Vdd to 1.77V from 1.7V. This is an increase of 4.1% and is almost exactly what a 1K across 51 Ohms should yield... So to get a: 0.1V increase needs a 860 Ohm resistor 0.2V increase needs a 435 Ohm resistor 0.3V increase needs a 300 Ohm resistor These values are approximate.... Happy Overclocking... -------------------- Too Many Computers,... Too Little Time ..... Damn Phenoms! Posts: 25194 | From: Fire Island, NY | Registered: Feb 2003 Polygon Admin Member # 1 posted                    Here's a great item for quick Mods. They can be purchased from DigiKey here in the States. They are made by "E-Z Hook" All they need is some #24 stranded wire to connect them in pairs... P/N: 461-1016-ND P/N: 461-1017-ND -------------------- Too Many Computers,... Too Little Time ..... Damn Phenoms! Posts: 25194 | From: Fire Island, NY | Registered: Feb 2003 Polygon Admin Member # 1 posted                    OK, I got a chance to try several values and here's what the parallel resistor needs to be. This is the resistor that will be connected from U20 pin 8 to U20 pin 3(ground): 1K--> 1.77V 470-> 1.85V 270-> 2.0V Next is to connect the resistor semi-permanently and do some testing... -------------------- Too Many Computers,... Too Little Time ..... Damn Phenoms! Posts: 25194 | From: Fire Island, NY | Registered: Feb 2003 Polygon Admin Member # 1 posted                    Bad news kids, I have now done the Vdd mod and got the exact same thing as without it. Here's a rundown of the system: AN35/N Vdimm and Vdd mods,Watercooled holding 30°C AQXEA 2500 0330 8X200 to start, used Clock-Gen to increase FSB; CPU is good for 2.3-2.4Gig Vcore= 2.0V Vdimm= 3.0V Vdd= 1.92V GEIL PC4400 11/4/4/3 Pass SuperPI @ 8X265; crash SuperPI @ 8X270 It must be that CPU won't go above 270... Results are here. -------------------- Too Many Computers,... Too Little Time ..... Damn Phenoms! Posts: 25194 | From: Fire Island, NY | Registered: Feb 2003 45 Auto Moderator Member # 236 posted                    Have you tried the mod along with giving the Ram 3.3volts? You might be maxing out the memory at 3.0. If memory serves me, Xbit labs found that the Ultra Platinum would go about 10-15mhz higher with 3.3. -------------------- 5400Brisbane/DFI Dk M2RS/Xigmatek HDT s1283/4gig OCZ Reaper 8500/ Radeon 4850/Enermax Liberty 500/Vista Ult x64 Asrock 939dualie/4200 AM2/6gig A_Data DDR2-800/BFG 8600GTS OC1/Antec Basiq 500/Vista Prem64 sp1 Posts: 1514 | From: Sacramento, Ca. | Registered: Oct 2003 Polygon Admin Member # 1 posted                    Not in conjuction with the this Vdd mod. I did the 3.3V mod when it first came to light and basically got the same results.... On the Jetway, performanced is increased with higher-then-default Vdimm, but stable overclocks are about 10Mhz lower(FSB) with the same parts... Maybe Alan can shed some light on this. Like what his best overclock is/was at around 30°C... -------------------- Too Many Computers,... Too Little Time ..... Damn Phenoms! Posts: 25194 | From: Fire Island, NY | Registered: Feb 2003 Polygon Admin Member # 1 posted                    Someone asked how I arrived at the final value. Here is the simplified schematic and the calculations to arrive at the final value of 270 ohms: The "job" of the regulation circuitry is to make the "plus" and "minus" inputs of the Error-Amp equal... -------------------- Too Many Computers,... Too Little Time ..... Damn Phenoms! Posts: 25194 | From: Fire Island, NY | Registered: Feb 2003 oldandslow Platinum Member Member # 290 posted                    To add to Polygon's post on the mini jumpers, just head to your nearest Radio Shack for these. Mini Clip Jumpers Already wired and ready to go. Pair, one black, one red. Enough for two voltage mods. -------------------- Shuttle AN35N/ 35w XP-M 2400+ IQYHA/ 2x256m Geil PC4400/ [10.5x245.6=2578 & 9.5x250.5=2380] Shuttle AN51R/ A64 3400+ Newcastle/ Tt Bigwater/ 1x512m Kingston HyperX TCCD/ [9x300.68=2706 & 8x325.5=2604] Posts: 1053 | From: Huntington, WV USA | Registered: Dec 2003

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