First post, by Masejoer
I have a later SiS 85C496/97 486 motherboard here that I've been trying to troubleshoot L2 cache issues for months. The board will only boot to DOS with L2 disabled. There is no pin, trace, or pad on the pcb for the VCC pin28 on the TAG chip. It came with a um61256fk-15 chip that has a jumper wire soldered underneath from pin28 to pin26, and this setup gets the system locked at "starting ms-dos". If I remove the jumper wire, it will post as far as the system spec screen, but no hard drive activity. Disable L2, works fine.
I pulled the known working (20ns) TAG chip and (25ns) SRAM from another board and installed it - a 128KB configuration. With jumpers setup correctly, it stalls on the system spec screen. Solder a jumper wire between pins 28 and 26, I get to the same "starting ms-dos" text, and same lockup. Disable L2 in BIOS, boots up fine again.
There is nothing for me to tweak in the BIOS, and there is no known later BIOS. A different CPU/jumper configuration doesn't work either. I've tried PCI and ISA videocards, different RAM.
Does anyone know why a board would exclude the VCC pin? And how would getting power from pin 26, an address pin, make sense?