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Thread: Replacing the screen of a Compaq Portable 486c

  1. #1
    Join Date
    Oct 2018
    Location
    Fontainebleau, France
    Posts
    3

    Default Replacing the screen of a Compaq Portable 486c

    Hello everyone,

    One afternoon, I was browsing leboncoin.fr (a French classified advertisement website) and found an intriguing ad for an "old computer" close to me with just a blurry picture and a dirt cheap price. Turned out it was a Compaq Portable 486c and I walked home with it
    Attachment 49136

    As could be expected, the computer was not working at all. When plugged and powered on, all I could hear was a small click every few seconds. I first suspected the power supply, but it ran fine when the computer was unplugged (stable voltages and the fans where spinning). After removing boards one by one, I identified the issue: the 5V supply was shorted to ground on the motherboard. Turned out the 486 CPU was dead. After finding the same model (in my case, a 33MHz 486DX), the computer could boot:
    IMG_20181013_184036.jpg

    Yeah! I could have a look at the content of the (still working) hard disk. Considering the presence of AutoCAD and various professional pieces of software, it is obvious that it was a professional computer for an engineer. No surprise, considering that they were sold for at least 6000 USD back then.

    But there is something obviously wrong on this computer. The screen is flickering a lot, everything is fuzzy and the colors are completely wrong. It is almost usable in text mode, but don't even think of running Windows (3.1, installed) or a game:
    IMG_20181013_184138_1.jpg

    After unplugging and re-plugging each of the ribbon cables (sometimes this helps), tweaking the calibration pots of the screen (changed the colors but no actual improvement to image stability) and having a look at the inside of the screen (looking for misplugged cable or bulged capacitor or anything obvisouly wrong), I concluded the screen is deceased. A quick search on the Web shows that is seems to be a very common failure mode of these computers.

    Then, I decided to sell it as-is on eBay but changed my mind: there is something I haven't tried yet. What if I could simply replace the screen?

    Part 1: What to buy?

    The manual of this computer (which can be found as PDF here, for instance) lists this part as 128902-001. The website impactcomputers.com claims to sell some for 80$ but this is a lie. Once you order and pay, they never ship and to have to open a complaint to get your money back. I wonder how much they earn from people placing orders and forgetting about them... Anyway, this is not the way to go.

    I could read the actual P/N of the screen on its sticker. It is a LQ10D016 from Sharp. New old stock can be found on Aliexpress for 165 (~190$) but I don't wish to put *that much* in repairing this computer. I went with my "plan B": buying a similar model and figuring out a way to plug it to the computer.

    The original screen uses a 30-pin ribbon connector. There are no datasheet available on the Web. Judging from how they are grouped in pairs on the VGA card, I assume this is some case of LVDS interface. It also provides 2 DC voltages: 5V and 12V. I could not find any other screen using an interface similar to this one. Anyone knows what it could be?

    Instead, there are many industrial screens with similar specifications (640x480, 10.4" TFT LCDs) sold all over eBay and Aliexpress using a way more standard D-shaped 31-pin connector (plus, mostly standard pinouts and available datasheet). So I bought a LQ104D1VG11 screen on eBay for 48 and a matching controller board (25). The plan is to connect to the computer using the VGA port instead.

    In the meantime, I simply used an external monitoring, reinstalled MS-DOS, Windows and put some games.

    I got the parts yesterday!

    Part 2: Receiving the parts and mounting the screen

    First, I unpacked everything and checked that it is working. The cable screen goes to the controller, the fluorescent tubes to the inverter board and the VGA cable to the computer. Yep, I works:
    IMG_20181102_190640.jpg

    One issue arises: how to mechanically install the new screen, which has different dimensions (generally smaller in all directions) and different screw holes. Also, I want to minimize the damage I inflict to the original hardware. This means I would rather avoid to drill holes in the case unless it is absolutely necessary.

    The solution I found? I retrieved the frame of the dead screen (which has all the proper mounting bracket) and installed the new one inside. Here is the frame without the screen:
    IMG_20181102_192252.jpg

    Here is my "step-by-step guide in doing a dirty job":
    1. Remove the following corner (using a Dremel) in the metal frame because the screen won't go in it otherwise:
    IMG_20181103_111003.jpg
    2. Butcher this corner of the screen. (Don't run away just yet, it is not *that* bad.) Beware at not damaging the nearby PCMs.
    IMG_20181103_110951.jpg
    3. Now using hot glue (hey, come back!), you can maintain in place the new screen in the frame of the old one. You can also glue the inverter board:
    IMG_20181103_120641.jpg
    4. You now get a replacement screen module for a Portable 486c!
    IMG_20181103_120442.jpg

    I installed it in the computer. It fits just right (obviously, it is the correct frame...) and now I can get rid of the external screen. The computer is at least somewhat portable:
    IMG_20181103_122220.jpg

    Obviously, I need to find a way of hiding the control board inside the computer and do a proper connection on the *inside* of the computer. My plan is to hide the board behind the screen (since the new one is significantly thinner than the original) and use a ribbon cable and proper connectors that fits through the opening on the inside of the case to connect the graphic card to the LCD screen. I will also need to find a 5V line big enough to support the screen but I guess the old inverter board should provide this (on its input!!!). I think this plan will work, and I will update on its status if you guys are interested.

    Final remarks:
    - The only thing that bothers me it that I will have to install a new connector on the graphic card and solder the adequate connections. This is a very benign operation but I hope this won't cause any damage to the board. Or do you have any better idea?
    - Also, I will need to change the keyboard cable, which is frayed. It should not be a big deal.
    - One strange thing is that sometimes the new display is pixel-perfect (for example Windows 3.1 running in 640x480 or many games running in 320x240) but the basic text mode on MS-DOS is not. Does anyone understand why?

    Cheers,
    felixzero

  2. #2

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    This is neat! Nice computer and nice build. It's hard to come by these old computers in my end of the world (Hong Kong) so I usually have to pay an arm and a leg for them on ebay, but your restoration looks pretty clean. I'm restoring another two compaq's at the moment - the more common Portable III (286) and Portable 386 (both with retro orange gas plasma displays) - the limitation with these devices is that they are CGA only, so most games have to be run via an ISA VGA card on an external monitor. The goal is to remove the floppy and maybe install an internal battery to make them truly portable. Check it out here: http://www.vcfed.org/forum/showthrea...q-Portable-386

  3. #3

    Default

    Nice work! The issue with the stock LCD panels are usually failed capacitors. The caps may have looked fine, but they were most certainly the issue and replacing them would have likely brought the LCD back to life.

  4. #4

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    Very nice. I found a similar panel to swap into a Compaq Portable III that fit perfectly. I also swapped out its guts (bought non-working off ePay) to make a portable Linux machine, but looks great running DOSBox:


  5. #5
    Join Date
    Oct 2018
    Location
    Fontainebleau, France
    Posts
    3

    Default

    Quote Originally Posted by resman View Post
    Very nice. I found a similar panel to swap into a Compaq Portable III that fit perfectly. I also swapped out its guts (bought non-working off ePay) to make a portable Linux machine, but looks great running DOSBox:
    Did you put a Raspberry Pi or something more powerful?

    Quote Originally Posted by uscleo View Post
    This is neat! Nice computer and nice build. It's hard to come by these old computers in my end of the world (Hong Kong) so I usually have to pay an arm and a leg for them on ebay, but your restoration looks pretty clean. I'm restoring another two compaq's at the moment - the more common Portable III (286) and Portable 386 (both with retro orange gas plasma displays) - the limitation with these devices is that they are CGA only, so most games have to be run via an ISA VGA card on an external monitor. The goal is to remove the floppy and maybe install an internal battery to make them truly portable. Check it out here: http://www.vcfed.org/forum/showthrea...q-Portable-386
    Thanks! They are also very rare in Europe! I looked for one also, even an out-of-order one, but nobody have them, and when they are sold, it is usually 300+. Color screen and VGA graphics make the Portable 486 great for gaming while still being portable. And I added a Soundblaster clone in one of the ISA port. There is a jack to redirect the audio output back to the internal speaker. Very neat design.

    Quote Originally Posted by compaqportableplus View Post
    Nice work! The issue with the stock LCD panels are usually failed capacitors. The caps may have looked fine, but they were most certainly the issue and replacing them would have likely brought the LCD back to life.
    Very probably, but there are about 20 of them, nearly all surface-mounted and of different values. I am not that patient!

    The bad news is that the (brand new) screen started flickering then slowly turned white and won't show any image anymore
    I think I might have put to much stress on the screen connector/cable with my temporary mount and I will check it. I hope the screen is not dead...

  6. #6
    Join Date
    Jan 2012
    Location
    Surrey,BC,Canada
    Posts
    143

    Default

    Resman..your LCD replacement looks great....anyway of sharing some info on the LCD. I, too have a Compaq III Portable (priginal gas plasma crt still works) but just making sure i have spare. Thanks

  7. #7

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    Quote Originally Posted by felixzero View Post
    Did you put a Raspberry Pi or something more powerful?
    I put an NVIDIA Jetson inside. Much more powerful than a RPi yet still leaves a lot of room for additional adapters and power supplies.

    Quote Originally Posted by RizThomas View Post
    Resman..your LCD replacement looks great....anyway of sharing some info on the LCD. I, too have a Compaq III Portable (priginal gas plasma crt still works) but just making sure i have spare. Thanks
    It is a 1366x768 panel with one of those generic controller boards that support VGA and HDMI. I bought it for another project that didn't pan out but just happened to fit the Portable III almost to a T. The bigger issue would be the placement of the controller board and power supply.

    Here is the album of additional pictures: http://www.vcfed.org/forum/album.php?albumid=313
    Last edited by resman; November 15th, 2018 at 08:39 PM.

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