First post, by athlon_p0wer

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A while back I made this thread: Extensive 486 Modification - Getting an IBM PC 350 Type 6581 motherboard into a Packard Bell Legend PB400 Case in which I described a horribly painful process of modifying my 486 in mostly destructive ways.

I've had to modify it some more because the system was turning itself on when I left it plugged in. I thought it was the PSU, but it was actually somehow the power button. I don't know how a power button would fail like that, given that all it does is bridge the circuit to turn the PSU on through the motherboard (the PSU uses a proprietary way of connecting to the system where the power button plugs into the motherboard, sort of like knock-off ATX functionality), but when I changed it out with a random garbage power button I had, it stopped doing it. Anyways, the new button couldn't fit like it was, so I had to cut a small piece of the front panel off to accommodate for the new one.

Other than that, I gave it a DVD-ROM drive because in my experience they read CDs far more reliably than any vintage CD-ROM drive I've used. Of course, I only am using the CD-ROM function of it. I also upgraded the RAM to 16MB so I don't have to worry about RAM limitations quite as much (for example I can now use smartdrv @ 1MB for DOS and 512k for Windows and still have 12MB free after everything else), and I gave it a 1.2GB HDD instead of the 540MB drive that came with it because I wanted faster disk access and didn't want to ever have to worry about hitting a storage ceiling, either. Two other things I've added are a small fan above the heatsink so that it can get some cooling going besides just the power supply fan acting as an exhaust (there is no place for an intake fan), and a Soundblater Vibra16S for better sound as the other sound card I mentioned in the other post was, I think, the Aztec card which had a modem integrated. I no longer have that card, but I never found drivers for it anyways.

Most of what's new with this machine is in the software. I have 614K of conventional memory free, despite having CD-ROM drivers, smartdrv, share, and doskey loaded. The way I've done this is by using QEMM (I will never go back to the inbuilt memory management in MS-DOS again), and loading everything that I can into the UMB, within reason. I've also switched to VIDE-CDD and SHSUCDX for CD-ROM drivers, and CTMOUSE for the mouse (which I load if I need it, otherwise I leave it unloaded). Even when I do load it, it goes to UMB anyways, so I still lose no conventional memory.

Overall, it runs better than it ever has with this combination. It is stable (knock on wood) and gets decent benchmark scores, too. In DOOM I actually gained a small performance boost, up from 27fps to 30fps using demo3 as a time demo, and things are snappier than they were before as well, both in DOS and Windows 3.11.

I should note that I removed the electrical tape off of the ISA riser, and sealed it with superglue. It looks much better now, but I don't want to open this thing up at the moment to take a picture.

It still looks rough, but this was never really a build for looks. It serves all the functions I need out of a 486, and that's all I've ever wanted.

File size
1.39 MiB
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Public domain

I have thought about putting a DX4-100, or ideally, a 5x86 133 into it to get a slightly smoother experience in DOOM and similar games, but it plays them just fine at default settings. I have become much more accustomed to low framerates due to working on this machine non-stop for a week or so.

Reply 1 of 1, by Warlord

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All depends on how your particular motherboard turbos. Some don't turbo right and a DX100 ends up just being way too fast. If it turbos down more than half like mine does than a dx100 can be a thing. Deturbo on a DX2 66 on mine makes it go too slow, so thats how you will know if its good or not.