Debugging a 386 motherboard...

Here's one for the PC gurus (I know there are a few of you here!) I've got the 386 motherboard on the bench. It's got four 1MB 32pin SIMMs installed (it can take eight), no graphics card and my POST code display card (which arrived in the post this morning). I've set the jumpers per the manual: http://stason.org/TULARC/pc/motherboards/I/INFORMTECH-INTERNATIONAL-INC-486… The CPU on this thing is an AMD Am386DX-40. The math-coprocessor (Intel 80387DX-33) has been pulled for now. BIOS is an AMI (American Megatrends) BIOS, label on the chip says Copyright 1992. This is the BIOS which has the atrocious magenta-and-cyan setup screen. The POST card is reporting stable power, RESET inactive, and a valid I/O clock. After powering up, I get the following sequence of POST codes cur prev -- -- holds for a second (or so) 02 01 holds for ~15 seconds 06 05 holds for a second 0d 0c holds for a few minutes 00 0d holds forever The POST card has two displays: CUR and PREV, for Current and Previous code. CUR is the code most recently written to the debug port, PREV is the one before that. Now, according to http://www.postcodemaster.com/AMI91.shtml , 0D is "CMOS Shutdown Register Test to be Done Next", and 00 is "Going to Give Control to INT 19H Boot Loader". Does anyone have any clue what these error codes actually mean? Complete guess here, but it looks like the BIOS is having trouble talking to the CMOS RAM chip. Going by the Dallas datasheet, the most likely candidate is that it's writing 01X (i.e. 0,1,something) to the enable bits in CR1, then reading it back to make sure the control register was set up correctly. The readback failed (repeatedly), so it got stuck in a loop. Obviously without a disassembly of the BIOS, it's pretty hard to say for definite that this is the problem... but does what I'm saying sound at least reasonably plausible? I'm thinking my next step should be to plug a couple of Harwin pin headers into the turned-pin socket and probe it with the logic analyser... Does anyone have any other ideas? -- Phil. classiccmp at philpem.me.uk http://www.philpem.me.uk/