The Asus P2B-S Rev 1.04. clock generator chip is an ICS 9250CF-08, capable of generating up to 150Mhz FSB. However, for reasons unknown, Asus crippled the chip by only installing 3 FSB jumper headers on the P2B-S Rev 1.04. mainboards. As a result, the mainboard cannot be jumpered for FSB speeds over 133Mhz, and the available 133Mhz setting overclocks the PCI bus to 44.33Mhz (FSB/3).
ICS 9250CF-08 Jumper Settings
The table above shows the full range of FSB speeds supported by the ICS 9250CF-08 clock generator. Since Asus omitted the FS3 jumper, half these settings are unavailable - only the lower half of the table, where FS3 = 0, can be used. In order to enable the remaining settings, we must add the FS3 jumper header and a 10K ohm programming resistor in position R137A.
FS3 Missing
The FS3 header and R137A are missing in the picture above
FS3 Installed
The FS3 jumper header and 10K ohm programming resistor have been added in the picture above. The required parts were removed from a defective mainboard.
The modified P2B-S Rev 1.04. was tested with a 1A Ghz Tualatin Celeron
CPU mounted on a Slot-T adapter, and a 256MB PC133 RAM module, both known
to operate reliably at 150Mhz FSB. Testing showed that the full range of FSB
settings supported by the ICS 9250CF-08 are now available, and that the mainboard
is stable at 150Mhz FSB.
Last updated March 22nd, 2003 by p2b@sympatico.ca