hardware fixes

Adding BF2 jumper on older Socket 7 mainboards

Most older mainboards featuring Socket 7 were designed for processors available at RTM schedule (RTM - release to market). Therfore manufacturers thought not of implementing multipliers higher than 3.5x because intel's flagship processor this time was a Pentium 233 MMX. It was designed to run with a 66MHz FSB (FSB - front side bus) and a multiplier of 3.5x (3.5x 66MHz = 233MHz). A Pentium MMX CPU has a maximum multiplier of 3.5x although some notebook versions (Tillamook) feature multipliers up to 4.5x but were manufactured using a different socket format (MMC - mobile module cartridge).

Later AMD introduced Socket 7 processors (K6, K6-2, K6-III) with frequencies above 233MHz (reaching up to 550MHz with K6-2 and K6-III). To get support for these higher multipliers AMD used an additional pin on Socket 7 named BF2 and raised supported front side bus to 100MHz. The resulting specification for Socket 7 was called Super Socket 7 (or SS7). But as Socket 7 and Super Socket 7 have the same layout you can add BF2 to your Socket 7 board with some simple wiring.

Two options are available:
Connect BF2 permanent (easy way) to ground (V36) or connect BF2 to ground (V36) using a jumper (requires some soldering). Keep in mind that status of BF2 is only of interest for processors aware of BF2 like AMD K6, K6-2, K6-III or Cyrix MII or IDT WinChip. Intel Pentium MMX, AMD K5 and rise mP6 ignore BF2. See the following table for the resulting effects:

  Normal
(no BF2)
BF2 full
connect
BF2 jumper
connect
BF2 BF1 BF0  
0 0 0 2.5x   2.5x
0 0 1 3.0x   3.0x
0 1 0 2.0x   2.0x
0 1 1 3.5x   3.5x
1 0 0   4.5x 4.5x
1 0 1   5.0x 5.0x
1 1 0   4.0x 4.0x
1 1 1   5.5x 5.5x
For a full list of all Socket 7 processors refer to this page. You don't need to modify your board if you want to use a multiplier of 6.0x as this is available by using the 2.0x multiplier (AMD K6-2 CXT and K6-III interpret 2.0x as 6.0x due to a different implementation by AMD).

Bottom view of Socket 7

AN O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   1   O   O
AM   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O
AL O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   2   O   O
AK   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O
AJ O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   3   O   O
AH   O   O                                                       O   O   O
AG O   O   O                                                       4   O   O
AF   O   O                                                           O   O
AE O   O   O  | |                                                  5   O   O
AD   O   O    |L|                                                    O   O
AC O   O   O  | |                                                  6   O   O
AB   O   O    |E|                                                    O   O
AA O   O   O  | |                                                  7   O   O
Z    O   O    |V|               B o t t o m                          O   O
Y  O   O   O  | |                                          BF0 --> 8   O   O
X    O   O    |E|                  v i e w                 BF1 ----> O   O
W  O   O   O  | |                                          BF2 --> 9   O   O
V    O   O    |R|                                                    O   G
U  O   O   O  | |                                                  O   O   O
T    O   O    | |                                                    O   O
S  O   O   O  |A|                                                  O   O   O
R    O   O    | |                                                    O   O
Q  O   O   O  |R|                                                  O   O   O
P    O   O    | |                                                    O   O
N  O   O   O  |M|                                                  O   O   O
M    O   O    | |                                                    O   O
L  O   O   O                                                       O   O   O
K    O   O                                                           O   O
J  O   O   O                                                       O   O   O
H    O   O                                                           O   O
G  O   O   O                                                       O   O   O
F    O   O   O                                                       O   O
E  O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O
D    O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O
C  O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O
B    O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O
A      O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O   O
                     1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3
   1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7


Materials needed:
BF2 permanent connection:
- A print of this guide. (Sounds silly, but don't forget to print this before you remove your Board ! )
- A short tiny wire OR
- A good temperature regulated soldering Iron with a tiny top. (choose ~325° C) OR
- A conductive silver pen

BF2 connection with jumper select:
- A print of this guide. (Sounds silly, but don't forget to print this before you remove your Board ! )
- A wire-wrap wire of 60cm length (also called enamel coated wire or Lackdraht). That's a wire insulated only by paint.
- A desoldering pump.
- A two or three pin connector, that will act as a jumper, or just a little switch.

It may be a good idea to put a sticker near the CPU socket with a warning about your mainboard modifications !

How to
BF2 permanent connection:
- Use a short tiny wire (no isolation !) of approx. 1cm and stick both ends into the holes W33 and V36 depicted above. Insert CPU. Ready.
- Use soldering iron and wire to connect pin W33 and V36 at the bottom of the Socket 7 as depicted above. Ready.
- Use a conductive silver pen to connect pin W33 and V36 at the bottom of the Socket 7 as depicted above. Ready.

BF2 connection with jumper select:
Get the wire and remove the isolation from the end and solder it carefully to pin W33. Connect another wire to pin V36. Solder other ends of the wires to your switch or jumper. Now you have to decide where to put the jumper !
I decided to use some glue to put it near the existing multiplier jumpers. Please watch out not to build any connections to existing wires on the mainboard which would cause shortcuts.