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This page is for all of you PC geeks out there that are doing things like overclocking your
celeron 300a processors.

Update: I now have a celeron 667 overclocked to 1GHz on the Aopen AX6BC...
Green text indicates new procedure changes or comments related to the 667.

Update: I now have a P3 1GHz overclocked to 1170MHz on the Aopen AX6BC...
Purple text indicates new procedure changes or comments related to the P3 1GHz.

Depending on the motherboard and when / where the 300a processor was made,
you may have to increase your cpu voltage to at least 2.2 volts. On some motherboards
(like the Abit BH6) you can increase the voltage in the BIOS. But what if you bought the
Aopen AX6BC? (Both are very good from what I have seen on the web.)

First of all, the default cpu voltage for the celeron 300a is 2.0 volts (1.65 for 667) (1.75 for 1GHz).
When the frequency is stepped up to 450/1000/1170 MHz then you may get problems booting
windows. Boosting the voltage allows the processor to have a cleaner signal (at least that is what I
heard). If you tape pins A119 A121 & B119 then you can fool the motherboard to provide 2.2 volts.

This all sounds good but what happends if one of the taped pins makes contact?
The following shows what happends when the tape (or nail polish) wears:
A119 contact then voltage goes to 2.6
B119 contact then voltage goes to 3.0
A119 and B119 contact then voltage goes to 3.4
Most people do not suggest going over 2.4 volts because you could fry the chip. Even some
think 2.4 is too high. So what do you do since over-clockable 300As are getting harder to find?

Forget about taping! If you are good with a soldering iron you can make your own adjustable voltage.
The following procedure was performed on an Aopen AX6BC but the idea is the same for all vcore
auto-detecting motherboards.

First of all...the disclaimer:

This procedure will void any motherboards warranty and you are doing the following at your own risk.

  • You will need a SCSI id selector switch with selector wires. (from an external disk enclosure)
  • Find where pins B120 A120 A119 B119 and A121 connect to the motherboard. (Slot1 connector)
  • Follow the etches back to the voltage regulator chip and label the five pins. (like below)
  • Cut all five etches with a razor blade near the slot1 connector. (bye bye warranty)
  • solder the SCSI ground wire (usually black or brown) to motherboard ground.
  • Using the following diagram, solder the SCSI id wires to the coresponding legs:
    ID#   1     2     4    (8 not required for 300a)    Usually 1 = red wire
                           (8 required for celeron 667)         2 = yellow wire
                           (8 required for Pentium 1GHz)        4 = blue wire
         B120  A120  A119  B119                                 8 = grey wire
          |     |     |     |     |     |     |     |     |     |
       |                                                           |
       |                                                           |
       |                                                           |
       |                                                           |
       |          Aopen AX6BC voltage regulator chip               |
       |                                                           |
       |                                                           |
       |                                                           |
       |                                                           |
          |     |     |     |     |     |     |     |     |     |
          |     |     |     |     |     |     |     |     |     |
         (A121 wired to internal switch to ground for celeron 667)
         (A121 wired to internal switch to ground for Pentium 1GHz)
  • Use an ohm meter to verify switch and wires are properly configured.(before powerup)
  • Mount switch to the outside of your chassis.
  • Set the SCSI id selector switch to ID 1 (or 7 with A121 closed) (or 9 with A121 closed)
  • Power up system at 300/667/1000 MHz check vcore voltage with motherboard monitor utility.
  • Voltage should be near 2.1 or 1.65 or 1.75 volts...If not shut down and check your work.
  • Vcore voltages correspond with SCSI id (A121 open)...Example: 1 = 2.1, 2 = 2.2....
  • Set SCSI id to 2 or 9 or 11 and change frequency to 450/1000/1170 MHz and boot windows.

    You're done (overclocked!!!).

    The SCSI ids for the new celerons (vcore 1.65 volts or less) are a little more confusing
    because voltages below 2.1 are stepped down by .05 volts. I know that you can buy a
    slotket (FC-PGA to slot1 converter) now but I had previously cut the etches for the
    voltages for the earlier 300a modification...Besides...You can still do this procedure
    to the slotket without cutting etches (replace the voltage jumpers with SCSI id select
    wires) and mount the SCSI id switch to the outside of the chassis.

    The same applies to the Pentium Coppermine processors (vcore 1.75 or less).

    This takes some time and patience but it is a nice efficient and easy way to change voltages.
    By the way...If you did not buy your motherboard yet...there is a new version of the AX6BC
    called the AX6BC Pro. This board has voltage stepping (in two .1 increments) in the BIOS.
    With 1 AGP, 4 PCI, 1 ISA, 1 PCI/ISA there is alot of room for expansion.

    This is what I have in my PC:
  • Aopen HX6 chassis
  • Aopen AX6BC motherboard (adjustabled CPU voltage modified)
  • Aopen PC100 128MB x 2 and 64MB x 1 memory boards (total memory = 320MB)
  • PC133 256MB x 2 and 128MB x 1 memory boards (total memory = 640MB)
  • 64MB of 320MB for a ramdisk (IE cache files and windows temp files)
  • 256MB of 640MB for a ramdisk (Apps now run from RAM as well)
  • Celeron 300A at 464MHz (103 FSB) / 1002MHz (100 FSB) / 1170Mhz (117 FSB)
  • Net-N-Dude fan set (modified five fans) / Golden Orb Cooler / Standard Intel Fan
  • ATI 3D RAGE PRO AGP 2X (built in TV tuner)
  • Adaptec Dual channel SCSI controller DPT Dual channel Ultra160 RAID controller
  • Channel 1:
  • ST34373N 4GB Seaagte Barracuda drive*  ST34502LW 10,000 rpm LVD Cheetah
  • ST34520N 4GB Seagate drive *
  • Channel 2:
  • ST31230N 1GB Seagate drive ST34502LW Seagate Cheetah striped with channel 1
  • ST31230N 1GB Seagate drive *
  • Caviar 3GB IDE disk for linux
  • TOSHIBA CD-ROM XM-6201TA (32 speed)
  • Ensonic Sound card (with Creative drivers)
  • 3Comm Fast EtherLink XL 10/100Mb Ethernet Adapter (to connect to cable modem)
  • 3Comm Fast EtherLink XL 10/100Mb Ethernet Adapter (for internet connection sharing)
  • Lucent Win Modem (if the cable goes out)
  • Loaded with Windows98 Second Edition
  • Loaded with RedHat linux 7.1 on IDE drive

    * * Normally powered off and used for software backup purposes.

    The backup is performed using the linux command "dd" but that process is for another day.
    Please feel free to email me if you have any comments about the vcore procedure or if you
    want a SCSI id chart to select voltages from 1.3 to 3.5 volts.

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