Short-circuiting the chip
Another way to clear the CMOS RAM is to reset it by short circuiting two pins of the BIOS chip for a few seconds. You can do that with a small piece of electric wire or with a bent paper clip. Always make sure that the computer is turned OFF before to try this operation.
Here is a list of EPROM chips that are commonly used in the BIOS industry. You may find similar chips with different names if they are compatible chips made by another brand. If you find the BIOS chip you are working on matches with one of the following you can try to short-circuit the appropriate pins. Be careful, because this operation may damage the chip.
CHIPS P82C206 (square)
Short together pins 12 and 32 (the first and the last pins on the bottom edge of the chip) or pins 74 and 75 (the two pins on the upper left corner).
gnd
74
|__________________
5v 75–| |
| |
| |
| CHIPS |
1 * | |
| P82C206 |
| |
| |
|___________________|
| |
| gnd | 5v
12 32
OPTi F82C206 (rectangular)
Short together pins 3 and 26 (third pin from left side and fifth pin from right side on the bottom edge).
80 51
|______________|
81 -| |- 50
| |
| |
| OPTi |
| |
| F82C206 |
| |
100-|________________|-31
|| | |
1 || | | 30
3 26
Dallas DS1287, DS1287A
Benchmarq bp3287MT, bq3287AMT
The Dallas DS1287 and DS1287A, and the compatible Benchmarq bp3287MT and bq3287AMT chips have a built-in battery. This battery should last up to ten years. Any motherboard using these chips should not have an additional battery (this means you can’t flash the BIOS by removing a battery). When the battery fails, the RTC chip would be replaced.
CMOS RAM can be cleared on the 1287A and 3287AMT chips by shorting pins 12 and 21.
The 1287 (and 3287MT) differ from the 1287A in that the CMOS RAM can’t be cleared. If there is a problem such as a forgotten password, the chip must be replaced. (In this case it is recommended to replace the 1287 with a 1287A). Also the Dallas 12887 and 12887A are similar but contain twice as much CMOS RAM storage.
__________
1 -| * U |- 24 5v
2 -| |- 23
3 -| |- 22
4 -| |- 21 RCL (RAM Clear)
5 -| |- 20
6 -| |- 19
7 -| |- 18
8 -| |- 17
9 -| |- 16
10 -| |- 15
11 -| |- 14
gnd 12 -|__________|- 13
NOTE: Although these are 24-pin chips,
the Dallas chips may be missing 5 pins,
these are unused pins.
Most chips have unused pins,
though usually they are still present.
Dallas DS12885S
Benchmarq bq3258S
Hitachi HD146818AP
Samsung KS82C6818A
This is a rectangular 24-pin DIP chip, usually in a socket. The number on the chip should end in 6818.
Although this chip is pin-compatible with the Dallas 1287/1287A, there is no built-in battery.
Short together pins 12 and 24.
5v
24 20 13
|___________|____________________|
| |
| DALLAS |
|> |
| DS12885S |
| |
|__________________________________|
| |
1 12
gnd
Motorola MC146818AP
Short pins 12 and 24. These are the pins on diagonally opposite corners – lower left and upper right. You might also try pins 12 and 20.
__________
1 -| * U |- 24 5v
2 -| |- 23
3 -| |- 22
4 -| |- 21
5 -| |- 20
6 -| |- 19
7 -| |- 18
8 -| |- 17
9 -| |- 16
10 -| |- 15
11 -| |- 14
gnd 12 -|__________|- 13
Once you have done that the board should be ready for this procedure (use the Award variant):
http://www.biosman.com/biosrecovery.html
If it doesn't work, time for a fresh programmed chip from
http://www.flashbios.org
or
http://www.badflash.com