First post, by majestyk
- Rank
- Oldbie
I recently bought an old full-AT 386 mainboard (SIS "rabbit" chipset) in non-working condition.
Some components like AT-power connector and keyboard connector were missing. After replacing the missing parts and cleaning everything this is what I found out:
- The two tantalum capacitors near the PSU connector in the -5V and -12V lines were shorted so I replaced all 4 tantalums there by 25V types.
- The manufacturer is "Modula Tech Inc.", it has the typical "MT / QC / OK" sticker and when I swapped the BIOS chip in another mainboard with the same SIS chipset it showed the ID "1266" in the AMI BIOS string.
- 4 traces at the corner of the CPU socket were interrupted, someone must have slipped a screwdriver when removing the CPU. I repaired all traces carefully.
- several contacts of the (16) SIMM sockets were/are corroded and worn out, so I replaced the first 4 sockets for a start.
- The 8 cache chips are missing (8Kx8), but the two TAG chips are still there (16Kx4).
- I could not find any info about the model number nor about the jumpering. There are nine jumpers in total on this board.
- When the mainboard starts, you can see it go through numerous POST codes, before it finally stops at "3C".
Video gets never enabled (tried 3 different ISA cards) and the speaker NEVER makes any sound, no memory test click sound, not the slightest click when turning power on, nothing.
I tried different SIMM sets in different banks (9-chip and 3-chip, 1 MB, 256K and 4MB), all possible jumper settings, with and without battery, replaced the (socketed) peripheral controller "82C206", tried with cache populated and without, checked for interrupted traces very carefully, but at the moment I´m running out of ideas.
The missing speaker sound and video seem th be the key...