49LF004A boot block problem - for experts

Hot-swapping and Boot-Block flash & Boot block flash and floppy support
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magician
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Joined: Tue Sep 25, 2007 10:20 pm

Since Monday morning, one of my PCs won't POST anymore, for no particular reason. :? A motherboard in question is an Epox EP-5EGA+, which is based on Intel i915G + ICH6R chip set, and uses SST 49LF004A (firmware hub) for storing Award (actually Phoenix) BIOS and its CMOS.

At first, board was returning POST code C3h, on its LED display, which means that there had been some problem with "Expanding compressed BIOS code to DRAM". But I've suspected that DRAM could be faulty and played a bit with modules (taking them off and swapping places), which produced C1h and undocumented AFh codes, both relating to RAM problem. Since no strong conclusion can be made from those symptoms, I've decided to clear CMOS with jumper and give it another shot, but after that motherboard just sits at code FFh, from the very moment I press power button. Fans are spinning, LED's are lit, but the screen is black and board just won't POST. Moreover, now it doesn't even goes through POST steps...

I had researched and found out that it's EEPROM (49LF004A) is actually a 4Mbit "firmware hub", made for Intel chip-sets, and uses LPI (low pin-count interface). That raised my hopes for hot-flashing rescue.

I had partial success with hot-flashing on SuperMicro PIIIDR3 motherboard, which is based on i840 (dual P3 with RDRAM) and ICH south bridge, and also has 4Mbit firmware hub, only it is original Intel 82802AB. I have Uniflash 1.40, which properly recognizes both EEPROMs (82802AB and 49LF004A) and motherboard's chip set (i840), and runs flashing procedure with Epox's original BIOS image (5ega4C22.bin). But...

It seems that boot block of the SST chip is somehow protected or motherboards implementation simply doesn't let you write to a boot block area. Flashing progress bar end all green, which is good, but write verification procedure reports error on one block near the end of the progress bar. Progress bar consists of 32 fields, and I got X in only one of them. Fifth form behind, to be precise.

Boot block on this BIOS should be 8KB in size, and is probably located somewhere at the end of the 512KB image. Since one field in progress bar account for 16KB of memory space in case of 4Mbit image, failing block is located somewhere between 432KB and 448KB of that image.

I've examined binary image with hex-editor and interestingly enough, there are two bytes (08 BF) in a batch of FFs, just before the beginning of that 16KB segment, and even more interestingly, the other 8KB half of that segment starts with E5 69, followed by alternating "00 00 FE FF", and then FFs until it reaches actual code which is located between 444KB and 446KB. The last 2KB of that segment is also empty space (populated with FFs). This really does look like a boot block. The question is, why I can't flash it? There are no BIOS write protection jumpers on this board. Should I try with another board?

Ugh, and another thing... I seem to have some sort of problem with my floppy disk controller on this SuperMicro board, which works great apart from that. I just can't use floppy disk drive, so I had to make a boot CD, and thus don't have a writable storage to which I could dump the content of EEPROM itself, just to check if this is a BIOS problem at all. :( Though, considering all symptoms it looks like one.

Any suggestions on how to resurrect this M/B?
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