Problem with 486SX board not booting. Assistance needed.
Problem with 486SX board not booting. Assistance needed.
Collected a unit with a 486SX processor and an unidentified motherboard lacking manufacturer labels. Features include five 16-bit ISA, one 8-bit ISA, and one EISA slot. Instead of receiving typical voltages (+5 or +12) at the ISA ports, I’m seeing -12 and sporadic 3.3 signals during POST testing. No error codes appear on the board. It seems hardware issues are likely, as correct jumper settings still trigger codes. Tested a PSU from Packard Bell in another system and it resolved; same problem persists here. All traces remain intact, but I found conductive traces near the battery area that produce signals. Used a Varta PRAM battery but removed it—no signs of explosion or leakage yet. My suspicion points to faulty tantalum capacitors close to the ISA connectors, possibly causing shorts or open circuits when they fail. I’m leaning toward bad capacitors and would consider removing RAM to inspect individual chips in each socket. There are six cache slots available; it’s possible they could be compromised during storage. Testing them might reveal further problems.
These older boards typically relied solely on beep codes for communication. Did you include a speaker if one wasn’t already present? Also, issues like corrosion and galvanic action can cause problems in older equipment, even though they’re not common with modern hardware. Dendritic growth might also be a concern.
Get full clear high definition images of the board so I can assist with identification.
If the board is FUBAR, it’s true many prebuilt makers produced their own boards back then, with little to no swapping. At that time, Tandy was largely absent, Packard Bell likely played a role in Hewlett-Packard’s early days, while Gateway managed to stay afloat until the late 2000s. A few lesser-known companies probably used more common generic boards. EP Technologies comes to mind—I owned a 486SX from high school. Is this intended for running old MS-DOS games?
I have an AGP slot—worth checking out. First, I’d remove it completely and wash it in the dishwasher. Then take it out and scrub all the contacts. Swap the battery or install a new one instead of replacing the whole thing since you already removed the old one. Maybe try posting it next. Looking for any info on this board, and I’d also like a picture from the back side. Cleaning it up might help with the photos. *Still searching, but it seems to be an Intel board.*
Lol, correct, it's still on the board. Sorry, I've got around five pages open with I486 boards right now. Thanks for understanding! XD
Here’s a revised version of your list:
The collection includes 486 chipsets that aren’t immediately clear, so you might have some clues. *This could help us focus on the right board.* ETEQ ET6000 "Cheetah", ETEQ ET9000 "Jaguar" single chip OPTi 82C481/482 "HiB chipset", WriteThru OPTi 82C491, WriteBack OPTi 82C493, WriteBack OPTi 82C495SLC/206Q, Write Back (2 chips, unbuffered VLB) OPTi 82C495SX/392SX/206Q, WriteBack (3 chips, buffered VLB for better compatibility but slower speed) OPTi 82C495XLC/206Q, WriteBack (2 chips)", OPTi 82C495S, Write Back (2 chips), OPTi 82C571/82C572 VLB, ISA "486/Pentium Writeback" (mixed 486/586 design, 64-bit SRAM, 32-bit DRAM)*SiS 401/402 ISA, OTEQ ET6000 "Cheetah", ETEQ ET9000 "Jaguar" single chip OPTi 82C682, 386/486WB EISA chipset OPTi 82C683, 386/486AWB EISA chipset OPTi 82C802G ISA, VLB (single chip version of 82C895)", OPTi 82C895/82C206 ISA, VLB SiS 401/402 ISA, SiS 406/411 EISA, VLB SiS 460 ??? SiS 461 ISA, VLB SiS 471 ISA, VLB SiS 496/497 ISA, VLB, PCI Symphony "Haydn" UMC UM82C491/82C493 ISA, VLB UMC UM8496/8498 ISA, VLB UMC UM8881/8886 ISA, VLB, PCI VIA VT82C496/82C505/82C406 ISA, VLB, PCI