First post, by NScaleTransitModels
I finally managed to obtain such a motherboard, so I could try my luck at a 486DLC + VLB build.
It's a UTD 4700 ALL IN ONE, made by Up-To-Date Technologies (never heard of them): https://stason.org/TULARC/pc/motherboards/C/C … ALL-IN-ONE.html
It came with a 486DX2-66, which booted flawlessly. However, as soon as I installed a 486DLC and switched it into 386 mode, that's where the problems began.
First, it would get stuck on the "WAIT" boot screen. I had to disable "auto WS and bus clock set" and add a cache wait state.
It was still not stable enough to fully boot from floppy, so I had to disable the Fast Gate A20 Option (not sure what this does).
After that, I was able to install Windows 95, and run games + benchmarks. However, I ran into more issues when trying to install NT 4.0 (as a stability test). It would be unable to copy files at random, and always lock up before completing the last graphical phase. It was not truly stable.
A memtest revealed countless errors within seconds (should've done this first, guess my excitement got the better of me). I tried tweaking several more BIOS/jumper settings, swapping stuff out, but the only way I could get the errors to go away was to switch back into 486 mode. Then even a DX2-66 @ 80 gives no errors.
Here's what I tried to no avail...
-486DLC vs. 386DX
-Memory sticks (4x4mb 60ns, tested fine on a different machine)
-S3 P86c805 VLB video card vs. Mach32 VLB and various ISA cards
-ISA Multi I/O card, disabling on-board IDE and floppy
-System Boot Up CPU Speed high/low
-External Cache enable/disable
-Internal Cache enable/disable
-Fast Gate A20 Option enable/disable
-auto WS and bus clock set disable
-Dram Read/Write Wait State, AT Bus Clock Selection, Cache Read/Write Hit WS, Burst Cycle WS— safest timings and basically all combinations
-VLB speed <= 33MHz, 40MHZ
-CPU speed 33 mhz, 40 mhz
-CPU type: 80386DX, CX486DLC (just marked as CYRIX on silkscreen)
-limiting cache to 128k
In conclusion, the motherboard works great when I plug in a 486, but as soon as I switch it over to 386 mode, it becomes unstable. Did I miss any BIOS or jumper settings that might make a difference? Maybe a cap went bad? Any input would be greatly appreciated.
PS. 486DLC + S3 VLB benchmarks from when it was stable enough to boot into Win95:
-3DBench = 25.0
-Doom = 11.656 FPS
- ECS FX-3000; 386DX-40@50; ET4000AX, ISA 1mb
- Acer VI9; 486DLC-40; Mach32, VLB 2mb
- Chicony CH-471A; CX486s-40; Mach32, VLB 2mb
- Gateway 2000 P5-60; Pentium-60@66; S3 928, PCI 3mb
- DTK PKM-0033S; AM5x86-133@160