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Thursday, February 4, 2010

Flashing BIOS via hardware

If you can't access the computer when it's on, and the standard backdoor passwords didn't work, you'll have to flash the BIOS via hardware. Please read the important notes at the end of this section before to try any of these methods.


Using the jumpers

The canonical way to flash the BIOS via hardware is to plug, unplug, or switch a jumper on the motherboard (for "switching a jumper" I mean that you find a jumper that joins the central pin and a side pin of a group of three pins, you should then unplug the jumper and then plug it to the central pin and to the pin on the opposite side, so if the jumper is normally on position 1-2, you have to put it on position 2-3, or vice versa). This jumper is not always located near to the BIOS, but could be anywhere on the motherboard.

To find the correct jumper you should read the motherboard's manual.
Once you've located the correct jumper, switch it (or plug or unplug it, depending from what the manual says) while the computer is turned OFF. Wait a couple of seconds then put the jumper back to its original position. In some motherboards it may happen that the computer will automatically turn itself on, after flashing the BIOS. In this case, turn it off, and put the jumper back to its original position, then turn it on again. Other motherboards require you turn the computer on for a few seconds to flash the BIOS.

If you don't have the motherboard's manual, you'll have to "brute force" it... trying out all the jumpers. In this case, try first the isolated ones (not in a group), the ones near to the BIOS, and the ones you can switch (as I explained before). If all them fail, try all the others. However, you must modify the status of only one jumper per attempt, otherwise you could damage the motherboard (since you don't know what the jumper you modified is actually meant for). If the password request screen still appear, try another one.

If after flashing the BIOS, the computer won't boot when you turn it on, turn it off, and wait some seconds before to retry.

Removing the battery

If you can't find the jumper to flash the BIOS or if such jumper doesn't exist, you can remove the battery that keeps the BIOS memory alive. It's a button-size battery somewhere on the motherboard (on elder computers the battery could be a small, typically blue, cylinder soldered to the motherboard, but usually has a jumper on its side to disconnect it, otherwise you'll have to unsolder it and then solder it back). Take it away for 15-30 minutes or more, then put it back and the data contained into the BIOS memory should be volatilized. I'd suggest you to remove it for about one hour to be sure, because if you put it back when the data aren't erased yet you'll have to wait more time, as you've never removed it. If at first it doesn't work, try to remove the battery overnight.


In Laptop


Important note: in laptop and notebooks you don't have to remove the computer's power batteries (which would be useless), but you should open your computer and remove the CMOS battery from the motherboard.
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

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