New project underway... Compaq 486 Revival!

edited July 2017 in Hardware
Quite a big project underway here.

I've been after a Intel 486 PC for years. They have shot up in value here in the UK in the past 5 years (£100+ on eBay) and i didn't really want to invest that much into one.

Recently one popped up on eBay, a Compaq Prolinea 4/25S with known issues for £25. I put in an offer for £10 and won it! It is complete aside from hard disk and is a little rough needs a good clean but the major issue is the keyboard doesn't work on POST and apparently the CMOS battery has leaked so I expect the PCB tracks to the PS2 port(s) are damaged.

I will desolder the old battery ASAP and replace it with a modern CR2032 + adaptor and hopefully repair the traces on the board. If not it does have 2 serial ports so i may be able to get away with a serial keyboard or adaptor.

Here is the machine.




I also plan to use a IDE to CF card plus adaptor on this machine I already have a Transcend 2GB SLC grade industrial CF card here and i've ordered an adaptor.


With all that installed etc it should be good to go! Fingers crossed I can repair the traces if that is what the issue is.

More soon...


  • Wow, hope it goes well and you can get it fixed! I would love to own something older then the two Pentium Pro chips I have. I'll have to look on eBay and see what kind of 486 I can find.
  • Thanks, yeah it was a pretty good find. Fingers crossed i can fix it up. Normally any 486 machines i see here (in the UK) are £100 - £150 ($200??) they have be rising in price for a while now and I don't really want to invest that much.

    The spec of the machine is:

    Intel 486 SX chip at 25Mhz
    4MB RAM (upgradable to 32MB)
    3.5" Floppy Drive
    (soon to be) 2GB CF card
    1MB VRAM onboard graphics with VGA out.

    OS planned: MS DOS 6.22

    Pretty strange that the 486 is actually soldered to the board haha! Makes upgrades pretty hard but honestly, if i can revive the machine and get it working then it will remain stock as i want to use it for really old DOS games.
  • I saw one like this for sale on ebay, as well, however I didn't buy it as it lacks an optical drive.
  • Yeah i was considering putting an optical drive in it but to be honest I want to keep this machine appropriate to its age/time period as much as possible. Also, any big games or files to transfer can be done so by removing the CF card and copying it over on my card reader on my main PC. Nice and simple.

    I have a PII machine which can do all my optical DOS/Win 95 gaming etc.

    This machine is purely an effort to save the machine from the scrap heap as well as have some fun on very old DOS games.
  • If you really want to refurbish a period-correct machine, look into getting a vintage hard disk. It's just not the same if the PC doesn't crackle like breakfast cereal every time it reads or writes the disk.
  • Yeah i know but I want to play around with CF cards (never used one on a old machine before) plus i love the fact i can pull the card out and add files really easily.

    It will remain a period correct machine aside from that so... a semi period correct machine I guess.

    I've also ordered a CR2032 battery + holder for it. Fingers crossed i can fix it up.
  • There was a time when I needed to move big files to an old machine. I took the drive out and plugged it into a newer desktop with an IDE controller and extracted the image straight to the disk. Aside from a couple of screws and some tape (don't ask), hard disks are typically very easy to remove from old systems. Especially this style case where the monitor sits on top.

    You don't necessarily need a holder for the CMOS battery. I got one from a friend that had positive and negative wires leading from tabs on the battery. I pulled the old battery off the board and soldered the wires to the pads. Secured the battery to the bottom of the case and it works fine.
  • 6.jpg

    Had some parts arrive. The machine itself comes in a few days... Should be good!
  • Ok the machine has arrived!




    Before even turning it on, it was straight into stripping it down for repairs and a much needed clean.


    The 486 SX processor. I thought it might have been soldered to the board but in fact it has a socket... 486DX/DX2 upgrade soon perhaps?


    ISA expansion module removed.


    Here is the big problem... a NiCD battery which is leaking like crazy.


    With the board removed i could see everything much better and it seems the underside of the board is fine. The top side shows signs of battery residue and some light corrosion on some of the components. Nothing too sinister though so far.



    Time to get that battery out of here!



    All gone! The eagle eyed of you may notice there is a cable running to one of the positive points on the board. This is in fact a cable for charging the battery. As i will be using a normal coin cell non rechargeable battery.. this charge cable can be removed.


    From here, it was out with the rubbing alchohol and q tips to clean the residue off the board.




    Much cleaner, looking good now. I have spotted one exposed track but it doesn't seem to be broken from what i can see.


    Time to install the new coin cell battery!




    Installed ready for a nice new battery.


    After this i booted the machine up for the first time to ensure everything was ok.


    All good apart from the issues the seller described which was the keyboard not working. I checked the PS2 port and it does appear to be getting power so I'm going to assume it is that exposed track which is causing the problem. That track is likely the data feed from the PS2 port so i will need to repair that trace.


    Before that though, I've decided to get the case cleaned up so that when the board is repaired it has a nice clean home to go back into.





    I also cleaned the PSU fan, it was caked in black crap.. I think this 486 was used in a warehouse of some kind in the past.


    I also cleaned up the plastics and metal. This was a tough job as they were all covered in gunk and crud from years past.





    Interesting message written on the top of the case.


    This machine has definitely been in some sort of IT infrastructure role in it's life.

    All cleaned, not perfect but it's the best i can do for now.





    Last bit, the rear plastic panel.



    Looking much better. Next up, tackling that PS2 port so i can actually get the machine going.
  • Off with your head!


    All the tracks seem intact...


    I got out the multi meter and ran continuity tests between the points and found one section which was broken even though it looked intact. The diagram below shows where (in red.)


    It was between a via and a component so i bridged these with a wire.



    PS/2 port back on...



    Sadly, still not working...


    I did wonder if it was my adaptor as i have no PS/2 keyboards. I tried one from next door and that didn't work either so more digging needed. During a little time out i browsed eBay and looked to see if any boards were around for this machine. Amazingly, there were lots of them! Seems there are more boards for these machines around than actual machines.

    They were around £35 but one which had just been listed was £15, I snapped it up quick because at that price... it's worth just getting a known working board and save myself the time and effort diagnosing this board further.
  • Maybe you could try getting a new PS/2 port assembly (or harvesting it from another machine) as it may be the port itself that is problematic.

    Did you try cleaning the PS/2 ports with compressed air yet?
  • i cleaned it with isopropanol rubbing alcohol so it was clean but like you say a new port would be better.

    This board won't be forgotten and will still be repaired when i get round to it. The new board iv ordered is a later revision board so can take DX/DX2 486's.
  • Nice.

    Is the CPU socket on the mobo a ZIF-type (Zero Insertion Force) socket or is it one of those older ones, which according to Lazy Game Reviews, required "jamming the CPU in there and hoping it would work"?
  • It's the older version so requires some force to put a chip in. Have to be very careful not to damage the pins.

    Ok, new board came, mixed results...


    Came with a CPU which was nice! A higher spec 50Mhz model.


    First things first was obviously remove that old battery! It was just starting to leak so caught it just in time.



    As you can see above, these newer revision boards actually have a track for charging on the PCB so no wire to remove. I could break the track but that would be messy and I actually got a proper socket and a rechargable coin cell battery rated at 3.6V so this will be much more original and clean.




    A very tight fit but it works and looks much cleaner.

    Assembling the machine..


    First power on...


    Nothing... Hmmm, I tried removing the RAM to see if the BIOS would beep and show me signs of life from the board... It didn't.

    Not good!


    I tried swapping out the processor with my 25Mhz chip, no joy!


    I also tried swapping out the BIOS ROM's


    One of my IC's was a earlier revision than it originally had but at this stage, try anything...


    Nothing.. Tried it with the later revision IC and one of the same models from my other board.


    Still nothing... Looks like a dead board... Next step will likely be removing the battery and sticking it into the oven and hope a re-flow will kick it back into life.

    Not having much luck with this machine. :(
  • One last ditch effort, re-flow...



    Sadly, still completely dead... Lost interest now, sadly this machine will shortly end up on the scrap heap.

  • keep it, and use ti for parts.

    You paid money for it, get as much use you can out of it.
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