Recovering BIOS Using BOOT BLOCK & BIOS PIN Shorting

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Recovering BIOS Using BOOT BLOCK & BIOS PIN Shorting

Postby ThEvil0nE » Mon Jul 25, 2005 1:57 am

This guide is not for the faint at heart. This type of Boot Block worked 8) on my bad-flashed notebook with hard-wired bios in which I did an I/O Port Boot Block many times before but failed. There is no guarantee that this might work for you but is worth a try before you decide to dumpstersize your mobo or you hard-wired- bios lappie :o

BIOS Boot Block Recovery: Pin shorting Guide

Introduction

BIOS chips, particularly the new ones have a built-in Boot Block sector, which allows the BIOS to be recovered if it is corrupted by a power mishap, misflash, or a virus. You really don't need to throw away a hard earned just to recover from a boot block mode. If you got guts and need to feel glory then read on.


AwardBIOS

The shorting trick should work if the boot block code is not corrupted, and it would not be corrupted if /sb switch was used when flashing the bios instead of /wb switch.

Image


Image


The two (2) pins used in shorting to force a checksum error vary from chip to chip. Usually these are the highest-numbered address pins (A10 and above). Most common are pins number 2 & 3. (refer to image) These are the pins used by the system to read the System BIOS (original.bin for Award V.6), now, calculate the ROM checksum and see if it's valid before decompressing it into the memory, and subsequently allowing Bootblock POST to pass control over to the System BIOS.

You just have to 'fool' the system into believing that the System BIOS is corrupt. You can do this by shorting the two (2) high address pins, thereby making it difficult for your system to read the System BIOS subsequently resulting to a ROM Checksum Error and activating a Bootblock recovery.

There will be cases that shorting any combination of the high address pins would not work to force a checksum error in some chips, like in the case of my Winbond W49F002U. Shorting the #WE (Write Enable) with the highest-numbered address pin (A17) worked for this chip. You just have to experiment a little if you're not comfortable with "Hot Flashing" or "Replacement BIOS". Refer to the chip's datasheet for reference.

If you're not sure which are the correct pins to short and avoid further damaging your chip, measure the potential between the 2 pins using a Voltmeter while the system is on. If the voltage reading is zero (or no potential at all), then it is safe to short these pins. But do not short the pins while the system is on. Instead, power down short the pins then power up. And as soon as you hear 3 beeps (1 long, 2 short), remove the short at once so that automatic reflashing from Drive A can proceed without errors (assuming you had autoexec.bat in it).

The tip of a screwdriver would do in shorting the pins but with such tiny pins on the PLCC chip, I'm pretty comfortable using a precision screwdriver. Short the pins at the point where they come protrude of the chip. Be careful not to short other pins as this might damage the CMOS chip or he mobo itself.



AMIBIOS


1. Copy a known working BIOS image for your board to a floppy and rename it to AMIBOOT.ROM.

2. Insert the floppy in your system's floppy drive.

3. Power on the system while holding CTRL+Home keys. Release the keys when you hear a beep and/or see the floppy light coming on.

4 . Just wait until you hear 4 beeps. When 4 beeps are heard the reprogramming of the System Block BIOS went succesful, so then you may restart your system.


Some Alternative Keys that can be used to force BIOS update (only the System Block will be updated so it's quite safe):

CTRL+Home - To restore missing code into system block and clear CMOS when programming went ok.

CTRL+Page Up - To restore missing code into system block and clear CMOS or DMI when programming went ok.

CTRL+Page Down - To restore missing code into system block and do not clear CMOS and DMI area when programming went ok


Important : Take note that the above alternative keys will work only on AMIBIOS V.7 or higher. An AMIBIOS V.6.26 can only be recovered by using CTRL+Home keys.



Flashing Without Video Display


AMIBIOS has integrated a recovery routine into the BOOT BLOCK of the BIOS, which in the event the BIOS becomes corrupt can be used to restore the BIOS to a working state. The routine is called when the SYSTEM BLOCK of the BIOS is empty. The restore routine will access the floppy drive looking for a BIOS file names AMIBOOT.ROM, this is why the floppy drive light comes on and the drive spins. If the file is found it is loaded into the SYSTEM BLOCK of the BIOS to replace the missing information. To restore your BIOS simply copy a working BIOS file to a floppy diskette and rename it AMIBOOT.ROM, then insert it into the computer while the power is on. The diskette does not need to be bootable or contain a flash utility. After about four minutes the system will beep four times. Remove the floppy diskette from the drive and reboot the computer. The BIOS should now be restored.



Recovering a Corrupt AwardBIOS


To recover from a corrupted AwardBIOS you will need to create a floppy diskette with a working BIOS file in .BIN format, an AWARD flash utility and an AUTOEXEC.BAT file. AwardBIOS will not automatically restore the BIOS information to the SYSTEM BLOCK, for this reason you will need to add the commands necessary to flash the BIOS in the AUTOEXEC.BAT file.


The system will run the AUTOEXEC.BAT file, which in turn will flash the BIOS. This is fairly easy. Here are the steps you need to take.

1. Create a bootable floppy diskette

2. Copy the BIOS file and flash utility to the diskette

3. Create a text file with any standard text editor and add the following lines:

@ECHO OFF

AWARD822 BIOSFILE.BIN /py


In the above example I am assuming that you are using the AWARD822.EXE flash utility. You will need to replace the AWARD822 with the name of whatever flash utility you are using and replace the BIOSFILE.BIN with the name of the BIOS file you are using. You will also need to change the /py to whatever 'command' is required for your flash utility to automatically program the BIOS without user intervention. If you do not know the command to automatically flash your BIOS type the name of the flash utility with a space and then /? to display the utility’s help screen. The help screen should specify the command switch to automatically flash your BIOS. If you are using the AWARD822.EXE utility then the switch to automatically flash your BIOS is /py.


Goodluck!
Last edited by ThEvil0nE on Tue Feb 06, 2007 2:43 pm, edited 1 time in total.
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Postby Abent » Mon Oct 16, 2006 7:03 am

I used the wrong code to flash the BIOS in my Asus cusl2-c mobo. It now boots to nothing on screen. There is no floppy activity at all. Could you please explain what the switches are. I do believe the board is destined to the dump. I think the all important boot block is toast too. But I am wondering if I could short some pins. I would be doing this in hope that I may be able to force the system to go to the floppy drive, which so far it hasn't. It does trip the HDD and CDD lights, and cpu fan & power is on.

Could you please explain what the /sb, and /wb switches are in your post. I looked and looked:

"The shorting trick should work if the boot block code is not corrupted, and it would not be corrupted if /sb switch was used when flashing the bios instead of /wb switch. "

btw I used the Asus aflash.exe bios utility in creating the problem and saved the orig, and wrote the wrong. No switches there. The overwrite boot block is a Y/N Boolean in order to proceed with the flash. Can you believe that s...t! Nice safeguard! Or maybe it would have proceeded with a No or whatever, on to the code, anyways it was inline, and I assumerd it was correct:;too late now.

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Postby apple_rom » Fri Apr 27, 2007 1:09 pm

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Postby evasive » Wed May 02, 2007 9:22 pm

Ah! Finally! Welcome aboard Sir!
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Postby ThEvil0nE » Wed Jul 18, 2007 11:10 am

Just using as reference for RK and RMS


thanx...
sineas :P
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having problem in flashing bios

Postby ali1289 » Sun Oct 07, 2007 7:49 pm

my problem is i have corrupt bios due to (improper flashing means my mobo is cusi-fxn and i flashed the bios of cusi-fx) after flashing the bios its says successfull but when i shutdown the system 7 open after that it seems to have problem in booting (detecting processor,ram,hdd,cd)but hangs after that and nothing happen further i'm not able to boot from any way or to flash it again . i also view urs method recovering bios by shorting pins and do that after shorting the pins it give 1long & 2shorts beeps and after that it gives another 2beeps and then after 20sec the led of floppy off's and system remains hang(all of this action perform in without display bcoz when i short the bios pins it not gives the display)


i have
celeron 733 mhz
asus cusi-fxn



So: plz someone help me to resolve this problem
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Postby jssdvnmyb » Sat Oct 13, 2007 11:28 am

I have a problem, too ;)

I have an Asus P5A Socket 7 Mainboard. Does it has a Boot Block Sector? Because BIOS is erased and I've tried to recover it by trying to create a disc with bootable system (DOS), flashtool, BIOS file and autoexec.bat, but when I start the computer nothing happens except that the cpu fan is rotating.
The trick with shorting the pins does not help as well. The Mainboard even does not beep on startup.
Don't know how to recover BIOS... thankful for every help!
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Postby madaload » Sat Apr 25, 2009 3:41 pm

In one forum I've been told that ASRock mobos, although they use AMI BIOS, cannot be recovered using FDD, because the System Block has been removed to save space. Is this true?
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Postby sharkonholiday » Mon Aug 10, 2009 1:38 am

i to everyone
i flashed a selfmademod bios into my netbook and i've bricked....
i've an asus 1000he (netbook 10") without floppy or dvd....
only 3 usb
how can i recover my bad bios?
it's an ami bios...
when i power on the netbook, it freeze on the asus logo without any possibility of press alt+f2, canc, tab, ....
help me please....
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Postby evasive » Fri Nov 26, 2010 12:15 am

madaload wrote:In one forum I've been told that ASRock mobos, although they use AMI BIOS, cannot be recovered using FDD, because the System Block has been removed to save space. Is this true?


yes :o you are right...
http://www.lejabeach.com/ASRock/html/as ... sguide.htm
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