Today I think I have made an important progress, for the resolution of the PINE SI21 failure, I had talked about it in another post (here : Identify motherboard Slot 1 SIS chipset ), the problem was basically somewhere, the post card stopped at post 41 0d with beep all 'infinite (as if the RAM was missing), but before the post 0d 0c it also made a long beep and two short beeps (video card problem), in short it was evident that there was something that was not in place, so it was thought that having the LED of the + 3.3V turned off that voltage was missing, and seeing that that voltage serves both RAM and the PCI and AGP, it was thought that this could be the problem to be solved.
In the search for the lost + 3.3V, they checked various mosfets and transistors in the MB, inductors and other things that caused an outage, but in the end after several checks everything seemed to be working, and so it was likely that the absence of that voltage was probably due to chipset failure (probably sud bridge), fortunately I do not have suitable equipment to remove and replace it (but I can tell this now), so I suspended the search for the fault and put the card away waiting for a different method to find the breakdown (which I did not know about).
Lately I have gained more knowledge of how the start circuit works, some things may be important, for example the battery always powers the MB (whether it is off or on), and the A14 PIN of the PCI is powered (usually ) when the PC is off but the power cable is plugged in (STBY), here instead there is no voltage in the PIN A14 of the PCI, I always read 0V instead of the 3.3V that are usually found, I see this in other MBs, so at this point it seems that there is nothing else to do, and just to see if I can solve at least the long beep and the two short beeps I try the video cards.
I reinserted the CPU and RAM, a PII 400 and a 64MB single sided PC100 with 8 GM72Vxxx chips, I start with an 8MB Intel 740 AGP (of a PIII 500 chipset i820), nothing changes, I switch to a Matrox Mystyque PCI I think 4MB, on this one there is an EZ1085CM used in many MB, even this test does not produce any effect, by now I had almost given up, but I have on the bench an old Western digital ISA video card with WD90C00 chip, the RAM on board it's maybe 64KB! (there are eight chips of the OKI M41464-10), it is possible to double it by finding another eight identical chips, however I start and the post card marks - -, I immediately turn off to see if something is hot enough, but nothing so I try again and after a some wait starts to display the usual post codes, until you get to the usual infinite beep!
But there is a very important news, the video displays something, it looks like the BIOS boot screen, in fact it is, but what it communicates is very important:
BIOS ROM checksum error
keyboard error or no keyboard present
Detecting floppy drive A media...
Drive A error. System halt
The message of the keyboard is correct because it is not connected, also that of the floppy is correct because I have not connected any drive, for the ROM checksum error I think it is due to the low battery, however if it looks for the floppy it is possible that it wants to do the BIOS recovery .
In this regard I have various files for BIOS update, and there are two different versions of the chip, which can be 1M or 2M, in the MB I have there is the 1M one (MX 28F1000PPC-12C4 chip), for this chip I have three different versions I choose the latest (most recent), it is used to update the Micro Code and fixes a compatibility problem with the ATI and TNT video cards, the installable CPUs arrive at the Celeron 500 and the PIII 600, but perhaps this depends on the Since these were the fastest CPUs available back then, maybe it's not hard for faster CPUs to run smoothly.
At the moment I'm still here, I have to prepare and put the file on a blank floppy, connect a 1.44MB floppy reader and an AT keyboard, then I have to reboot and see if the BIOS resets, in case it doesn't update I should see to do a reprogramming the chip, or finding a new chip and programming it with the right file, there would be a third shorter route, hot reprogramming using another PC with the same BIOS chip socket, is risky but fast enough and effective if done in the correct way you find yourself with two PCs working, otherwise if something goes wrong and you are wrong, having bad luck you find yourself with both PCs knocked out.
AMD 286-16 287-10 4MB HD 45MB VGA 256KB
AMD 386DX-40 Intel 387 8MB HD 81MB VGA 256KB
Cyrix 486DLC-40 IIT387-40 8MB VGA 512KB
AMD 5X86-133 16MB VGA VLB CL5428 2MB and many others
AMD K62+ 550 SOYO 5EMA+ and many others
AST Pentium Pro 200 MHz L2 256KB