I found a 486 board circa 1991 on ebay that was having keyboard issues so I grabbed it not knowing much more than that, When I received it, it seemed to be in really good condition otherwise. It’s a Biostar MB-1420/25/33PB/PV
This is a no frills 486 board, no cache no nothing., it has a 66MHz clock tho so its got that going for it.
Inbuilt CPU
https://www.cpu-world.com/CPUs/80486/Intel-KU80486SX-25.html
The Issue
As expected it was the good old leaky NiCAD trick which ate out the two keyboard CLK and DATA traces, (also had a good crack at the “Power Good” signal but it seems to be fine, for now)
The Repair
Trace back
Hiding under the keyboard controller is the 7407
BIOS
BOIS Dump
First Boot
Port 0x80
This boards chipset doesn’t have port 0x80 support so the standard diag cards didn’t help here
Booting
was still getting 8 beeps, turns out the ram was imbalanced,
Configuration
Going Forward
Overdrive Time!
The one I have is a DX2OPDR66, the 168pin “ODPR” version but this board has a empty 169th pin for the “ODP” version of the upgrade… shrug,,,
https://www.cpu-world.com/CPUs/80486u/Intel-DX2ODPR66.html
