Erik_
486 Overdrive Chip Installed!
Sun Feb 09, 2020 4:57am
24.190.98.110

Chip came earlier than expected from Hong Kong (Was originally expected to arrive 02/21).

With some contact cleaner, I installed the new chip.

I was mistaken, the socket didn't say it JUST took a 487, it just said "Upgrade socket" with jumpers specific to the 487. Interestingly enough it has the upgrade socket as well as the Weitek chip math co-processor upgrade. Those CPUs are apparently rare and only actually work on a small number of CAD software. Also the fact the board takes both chips is also pretty rare and usually only in "higher end" boards. This computer wasn't really a top of the line machine, but I guess it wasn't as "meh" as I always thought either...

Before CPU was installed:


The Weitek specific FPU upgrade socket:


The ODP486-25SX Overdrive CPU installed and jumpers moved. You can see the 486SX-25 surface mounted CPU peaking out from under the floppy disk bay in the top part of pic:


BIOS now shows "Upgrade-25" as the main processor and "Internal" as the numeric co-processor when booting. It use to say "486SX-25" as the main and "None" as the co-processor" before the install. Interestingly enough some benchmark software crashes now because the chip being reported is "Upgrade-25" which isn't in the list of cpu names.


This cache memory also isn't populated. I'd love to populate this as well but I'm not sure what chips would fit here. Any ideas?



The upgrade to the new chip is super noticeable. I can now play Doom in full screen with Hi-res enabled without any slow down. Previously, I would have to play in low-res in a 1/2 sized window when sound was on or a mostly full window in low-res without sound to be playable.

Duke3d is actually playable as well. The first level is playable in hi-res full screen. There's some serious slow down in larger levels though where even low res is "meh". The fact it's playable at all is super impressive though. Previously, even in the smallest window in low-res it was still basically a slide show.

Checking some benchmarks it's now reported as a 486DX2-50MHz which is cool. The 75MHz option would have been better but the price difference isn't worth it. I'm sort of bummed I didn't do this 20 years ago when I actually used that computer daily.. especially now that I know that it could have taken any 486 chip in the upgrade socket.


Edit: Side note. The 5 1/4 floppy is currently a 360k because I use it to copy files to my XT. There's also a 1.2MB 5 1/4 floppy in the computer but it's not hooked up because there's not any more cables to hook any more drives up.

    • Oh wow, that's awesome! - Puckdropper, Sun Feb 09 2020 3:41pm
      You mean you coulda stuck almost any 486 in that socket? Wow. I seem to remember having some cache chips somewhere, but Google is of no use telling me what cache chips that motherboard will use. It might be worth popping the chip number (once you find it) into Digikey or mouser just to see what... more
      • a 100MHz DX4 though. Also I think because it's originally a 25Mhz, I need to keep in line with that multiplier of 25/50/75. The 33MHz systems have 33/66/100Mhz options. Seems like the poster of this thread has the same exact computer and was able to get the external cache working after a huge hea... more
        • Does your board support 33 mHz? - Puckdropper, Tue Feb 11 2020 4:53pm
          I wonder if you can tell it it's 33 mHz * 3 and run it that way? Looks like Mouser might have some static RAM chips still. I'm not sure if the numbers are right or anything, but the most expensive was like $4.25 for one. Not exactly cheap but not out of reach either.
          • I know some boards do... - Erik_, Thu Feb 13 2020 5:47am
            There's usually a jumper setting for it. I'm not sure mine does because the 25Mhz chip is surface mount and not socketed (so it shouldn't expect the base CPU to ever change). I'm kicking myself because I had all the books for everything up until I moved out of my Mom's house 10 years ago. At th... more
            • Any chance of finding that board online? - Puckdropper, Fri Feb 14 2020 1:52pm
              There used to be TH99, but unfortunately there was never an official repository AFAIK. mf_2 got the copy for Uncreative Labs somewhere... Well look that that: http://oldcomputer.info/log/index.php?id=20161011213039-so-who-made-th99 Wonder if anyone is around to do updates?
              • No luck as of yet... - Erik_, Tue Feb 18 2020 5:05am
                I believe Vtech/Laser used a generic board from Hong Kong (about the only markings I can really find on the board). There's not really much info on it and there doesn't appear to be much info online for these computers at all. I took a look through the links for the TH99 pages but only f... more
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