First post, by Xaleros
Hello, I'm not sure if this is the correct forum category but from what I've seen I think this fits here. I'll try to keep this as organized as possible
I recently found a boxed copy of The Ultimate Doom at a Goodwill and decided that now was as good of a time as any to get some kind of DOS gaming machine going. Luckily for me, a friend of mine had a 486DX4-100 build that he had gotten awhile back. He didn't use it a whole lot so he offered to give it to me instead. After a dead 3.5" floppy drive and some driver hunting, I finally managed to get DOS installed and the CD-ROM drive working. Installing Doom worked fine and once I started the game, I was greeted with an awful framerate (I wanna say about 10-15 FPS, from what I've seen on youtube it almost looks like a 386 is running it). If I shrink the screen size to about half it runs fine.
I began troubleshooting a number of things, none of which had any effect. Eventually I did more digging into what motherboard I have and found this forum post -> 486 VLB UMC-Chipset, what is it?
I've read through this forum post top to bottom several times and triple checked the jumper settings on the motherboard. Some things I tried were:
- Running without sound or music
- Running without the CDROM driver
- Running without HIMEM or EMM386
- Running with only one of the two 16MB EDO sticks that I have.
- Running without any external cache enabled
- Running with failsafe BIOS settings
- Changing the jumpers for the CPU clock speed (Combination of JP5 and JP6 seem to have very strange behavior)
- Changing the jumpers for the CPU type (BIOS says "i486DX4" despite the cpu being configured for Am486DX4-100, I don't think that is correct)
- Setting cache read/write waitstates to minimum
- Running with only necessary ISA perphierals (Floppy/HDD controller, vga card, etc)
The only lead I have is that when I probe the CLKMUL pin, it does not seem to be high as it should be if it is in use, based on the manual for this CPU. I've been at this problem for about three or so days and I'm pretty much at wits end. Is there something really simple that I haven't done yet that is preventing the CPU from running at full speed or is the motherboard damaged and/or missing components? Below is a list of specs and pictures of the output after POST, the jumpers for CPU speed, and the jumpers for CPU type. Try not to mind my horrible phone camera, I labelled which jumpers are which to avoid confusion. Let me know if I need to post any extra information.
Specs:
CPU: Am486DX4-100NV8T
Motherboard: F4DXL-UC4D
RAM: 2x16MB EDO 60ns
HDD: Seagate Medalist 4321 4.3GB
ISA Peripherals:
PT-604A HDD/Floppy Controller
Mitsumi 74-1645A CDROM Controller + Drive
Sound Blaster 2.0 CT1350
Linksys Ether16 LAN Card
Trident TVGA900A
CPU Type Jumpers:
CPU Speed Jumpers:
POST Output: