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Thread: Toshiba T1200 internal power supply issues

  1. #1

    Default Toshiba T1200 internal power supply issues

    Having some issues with the internal PSU on the Toshiba T1200 I got recently.


    When I first got it, I noticed all of the caps were leaking, and the entire PCB was covered in electrolyte, so I washed the PCB and replaced all caps.


    Now when I plug it in, the green light comes on, but when I flip the switch, nothing happens. The motherboard board definitely works, because I was able to get it to fire up by connecting 5-volts directly to the motherboard's power connector. It booted from a floppy disk and everything.


    Here's a pic of the PSU (the two big caps are bent over because the replacements were quite a bit taller than the originals, but they are fine):


    thumbnail_IMG_4928.jpg


    Is there a component that commonly fails on these? Or has anyone successfully replaced the internal PSU with something else? There's a lot of connections though, so that wouldn't be too easy I don't think.


    And yes, the fuse is good. I've resoldered almost everything on the top side of the board to no avail.


    Always loved the T1200, so I'd really like to get this thing working! Also can't wait to see if the funky JVC 26-pin hard drive works too.


    Thanks!
    Compaq - “It simply works better”

  2. #2

    Default

    Well, I tried to replace one of the chips on the board, and now the light just “blips” on the board. Put the original chip back, and the same thing still happens. Don’t know what happened. I have replaced SMD chips in the past with great success.

    I think I’m just going to search for a parts unit now. I’m getting a little tired of all this eye and neck strain to get nowhere.

    Surely if I get another unit I can get something that works.
    Compaq - “It simply works better”

  3. #3

    Default

    Hi! I have the same problem with my T1200. My board is also partially corroded (I've washed it but it#s not helping).
    I think I will try to use external power sources instead of the PSU to check if the laptop actually working. Main problem will be emulating signals that PSU should send to the main board (it T1200 don't have it -- I don't know).
    Also it will be hard to find a device providing 22V.

    Quote Originally Posted by compaqportableplus View Post
    Well, I tried to replace one of the chips on the board, and now the light just “blips” on the board. Put the original chip back, and the same thing still happens. Don’t know what happened. I have replaced SMD chips in the past with great success.

    I think I’m just going to search for a parts unit now. I’m getting a little tired of all this eye and neck strain to get nowhere.

    Surely if I get another unit I can get something that works.

  4. #4

    Default

    Quote Originally Posted by l4l View Post
    Hi! I have the same problem with my T1200. My board is also partially corroded (I've washed it but it#s not helping).
    I think I will try to use external power sources instead of the PSU to check if the laptop actually working. Main problem will be emulating signals that PSU should send to the main board (it T1200 don't have it -- I don't know).
    Also it will be hard to find a device providing 22V.
    The internal PSU in these (and all of Toshiba’s early battery-powered laptops) is utter garbage. If you come up with a solution I would love to hear it, but until then these machines are on my blacklist and I will be avoiding them.

    Stick with the AC-powered units like the Toshiba T3100e. They are much better. If you want a good, early battery-powered laptop, get a Zenith. Those are very reliable in my experience.
    Compaq - “It simply works better”

  5. #5

    Default

    Quote Originally Posted by compaqportableplus View Post
    The internal PSU in these (and all of Toshiba’s early battery-powered laptops) is utter garbage. If you come up with a solution I would love to hear it, but until then these machines are on my blacklist and I will be avoiding them.

    Stick with the AC-powered units like the Toshiba T3100e. They are much better. If you want a good, early battery-powered laptop, get a Zenith. Those are very reliable in my experience.
    Thank you for the answer!

    So far my research is here, I'm going to do a bit of reverse engineering to understand how it's working: https://docs.google.com/spreadsheets...it?usp=sharing

  6. #6

    Default

    About the original PSU: I have changed all capacitors and the fuse.
    Result: now at least LED is green when PSU is turned off. When it's turned on (switch S1) - LED is red and blinking.

    My checks of outputs with multimeter:
    - PJ4: everything is 0 except two pin which are about 5V (one of the is supposed to be 5V, another is unspecified).
    - PJ2: 12V instead of 5V


    Good news: I have found a patent for this PSU (or very similar one) and it is expired: https://patents.google.com/patent/US5239495

    I did some rev.eng. and have restored most of the PCB connections except ones under the IC14 (TMP47C440AF - that it the main controller). I have the image of the PCB itself.
    And it looks like failure to provide 5V in PJ2 comes from the out 4 of IC14. TMP47C440AF is currenly rare thing to find at it is about $10 (not sure about quantity - it could be that minimal order is 100 pieces or so)
    .

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