First post, by davidrg
Lately I've been building myself a 486DX4-100. This is probably the first 486 I've built in 15 years (I got distracted by unix workstations for a while, plus less free time when I finished university) and has been quite a lot of fun. Enough that I'm tempted to build more - perhaps recreate my families first computer that could play games (a 166Mhz Pentium) and maybe a 386.
Here is the machine in all of its yellowed glory (just booted to windows so the CRT, a Panasonic PanaSync E70i, would be less of a mirror):
The specs so far are:
CPU: AMD Am486DX4-100
Motherboard: DataExpert EXP4045
RAM: 32MB 60ns Fast Page
VGA: S3 805 VLB, 1MB RAM. Digital part# PC76H-EA originally out of a DECpc LPx (sadly I never owned the machine).
IO: 16bit ISA Winbond UN1072
Network: 3Com Etherlink III 3C509B-TPC
Audio: SoundBlaster ViBRA 16 CT2810 with a DreamBlaster X2GS
Gravis UltraSound Classic rev. 3.4
Drives: 200MB Western Digital Caviar
1GB industrial type CF Card
32X Mitsumi FX322M 32x CD-ROM (I would have preferred 4x but didn't have one handy and the 32x looks pretty much identical)
1.44M 3.5" Mitsumi/Newtronics D359T3
1.2M 5.25" Teac FD-55GFR
I set out specifically to build a fast(ish) 486 so part of my reason for grabbing this particular case from storage (aside from the built-in speakers) was my belief that it was a DX4-100. Seems at some point in the distant past I upgraded it to a 100MHz Pentium - probably in 2004 based on the dates on the hard disk. The soldered RTC chip in the Asus motherboard was dead so the motherboard & CPU have gone into an antistatic bag back into storage.
I imaged the hard disk that was already in the case before wiping it for this new build. I could have just done everything off of CF cards but I kind of miss the hard drive noises - it feels kind of weird loading games from the CF card in silence. Sadly the mounting bracket for both the hard disk and 3.5" floppy drive were gone when I first got the case 20+ years back so previously I held the floppy drive in place with duct tape and let the hard disk rest on the bottom of the case. At the moment I can't find my duct tape so I've just got to be careful when inserting 3.5" disks. The cable mess seems to provide enough resistance that the floppy drive doesn't push back into the case too easily.
Getting it going was a bit of a challenge. Somehow I'd managed to avoid learning that there was a difference between FPM and EDO - back when I was in high school some 72pin ram just didn't work in some computers and it was a mystery as to why. Now I know why and my big box of RAM is now sorted.
Expansion cards were the other issue. Somewhere I have a box of VLB cards including some that are apparently quite fast for DOS (ARK1000PV and ExpertColor DSP6430/C&T F64300) and a bunch of I/O cards but I can't for the life of me find it. The only VLB cards I could track down were the S3 805 I'm using now and some NOS Pine cards that have an annoying option ROM. The S3 card seems nice enough though and the Winbond I/O card is at least stable. There is a little bit more detail on the S3 card in this thread.
Additionally, it seems like the 2nd 16bit ISA slot (second one up from the GUS just below the I/O card) doesn't work which caused a lot of confusion when I was trying to get this setup to POST reliably as at first I had a random VGA card in there. Sound cards installed in that slot simply don't work, and if I put the NIC there the NIC driver crashes on startup. No idea why but aside from a SCSI card I can't think what else I'd want to put in this machine anyway so its not really a problem.
As for the audio setup, the case has a pair of 5W 4 ohm magnetically shielded speakers in the front along with headphone and microphone jacks. IIRC they sound pretty good but I don't think I've heard them properly in 20 years because the volume control knob no longer works (the reason this case went into storage way back then). The toggle button next to the audio jacks is for switching between SoundBlaster and CD audio. I'm feeding CD audio into the sound card so for now its acting as a mute switch. I was tempted to see if I could rig it up as a SoundBlaster/GUS toggle but I don't think I'll bother now.
I'm now feeding the GUS line out (more like speaker #2) into the ViBRA 16s line in and then feeding he ViBRA 16s line out to the case speakers and this seems to work pretty well. No switching between sound cards, I just have the SoundBlasters line-in set such that games using the GUS are about the same volume as games using the SoundBlaster. I would have set it up the other way round and fed the ViBRA 16 into the GUS line in for less noise but... the GUS mixer doesn't work at all and the card is always at max volume, where as the Creative mixer works just fine. I spent a while trying to make the GUS mixer work but perhaps it only works for certain applications or for the newer PnP cards. The 3rd 3.5mm audio cable in the back is just to hook up the front microphone jack. I very much doubt I'll ever use it but figured I may as well connect it up anyway.
Things still to be done:
-
Replace the (not yet leaking and still holding a charge!) soldered NiCd battery with a CR2032 (holders are slowly making their way from China) -
Expand the GUS to 1MB -
Replace the stereo volume control potentiometer -
Add a DreamBlaster X2GS (on its way - I didn't pay for tracking so I guess it will just be a surprise in the mail eventually!) - Duct tape the floppy drive in place 🙁
- Figure out how to feed the PC speaker into the SoundBlaster so I can use headphones (I've seen a couple of different wiring diagrams for this, all with missing details and some with warnings about hardware damage if you do it wrong)
- Maybe patch the BIOS to fix its Y2K issue (it thinks its 2094). I'm running an NTP client on startup which sets the time correctly so its not really much of a problem at the moment.
- Replace or lubricate the PSU fan (its noisy when cold)