Testing of the Asus P2B-DS Rev 1.06 D03 mainboard at 150Mhz FSB showed we had a serious
problem with memory errors. The memory used for testing was a pair of
256Mb Corsair PC150 CAS2, model # CM654S256-150C2. This memory had
tested clean on the P2B-S at 150Mhz
FSB, so we knew the problem must lie with the mainboard.
Memory is nominally rated for a supply voltage of 3.3v, which is
provided by the ATX power supply, then regulated by the onboard
HIP6019BCB regulator. The regulated 3.3v supply is known as Vio.
Measuring Vio on the two mainboards revealed a significant difference:
P2B-S was supplying 3.47v to the memory, while the P2B-DS was regulating
Vio to 3.22v. Could this be the cause of our memory errors?
The HIP6019BCB regulator's VIO output is resistor-programmable from
3.0v to 3.5v. The programming resistor on the P2B-DS is R50, located between the HIP6019BCB
regulator and the first CPU slot.
R50 Location
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R50 Replaced
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The screen shot shows voltages
as reported by the BIOS after the Vio modification. The +3.3v voltage
read 3.2v before the modification, and is now reported as 3.5v. I have
no idea why I had the -5v voltage set to ignore when this shot was
taken, it should be -5.1v Since the second modification to increase Vio from 3.41v to 3.49v did not produce any improvement in the memory testing results, we recommend others planning this modification use a 4.7K ohm surface mount resistor to increase Vio to approximately 3.4v |
The modified P2B-DS successfully ran memtest86 for 48 hours without error at 140Mhz FSB - this appears to be the upper FSB limit for stability on the P2B-DS.
Last updated May 4th, 2003 by p2b@sympatico.ca