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Thread: Toshiba T1900C

  1. #21

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    Quote Originally Posted by DankEngihn View Post
    One last thing. Did you have the power supply plugged in? If so, remove it, and try again.
    first no psu, while I gave 12V to the battery leads on the mobo.
    I did try also giving both, 19V psu (to the pwr connector) and 12V to battery leads, but that changed nothing either.

    I did notice now that that 3V lithium battery what was earlier removed, is rechargeable.
    That may be why it still had 3V voltage - a couple of days ago I did have the psu connected over night.

    Still wondering, what is the purpose of that second dead, small finger battery.

  2. #22

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    It might be the RTC battery. If so, it needs this to post.

  3. #23

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    Quote Originally Posted by DankEngihn View Post
    It might be the RTC battery. If so, it needs this to post.
    batt.jpg

    I found out from t1900c maintenance manual about the batteries. RTC battery is in fact that rechargeable 3V lithium battery.
    I connected it and tried to boot -> still no change.

    Next, I was thinking to make the printer port led tester. It would not be very difficult to make, but I also noticed, that
    there are bios configuration requirements for it to work, thus it maybe not helpful after all.

    pport.jpg

  4. #24

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    Just found out information that there is a 5amp fuse on the lower system board and 2 amp fuse(s) on the higher system board.
    I have not checked these, since I was not aware of them before, but they go on the check list now.

  5. #25
    Join Date
    Oct 2016
    Location
    Dutchess County, New York, USA
    Posts
    89

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    Go ahead and check the fuses, always a good check.

    In your 4th photo showing the power supply there's two light blue electrolytic cap's and both have bulged tops, a sure sign that they need replacing. Others ???

    Check the RTC/BIOS battery for 3vdc to see if it is still okay - with main power removed. Then test again with power plugged in to see if there's voltage higher then 3vdc charging the battery. I doubt if a bad battery would prevent a boot, but while in there testing that's a test of the poweer supply to see if there's any voltages coming out of it (them).

    Also check for voltage going to the on/off switch since it needs to have power at all times so that the laptop can be turned on. On newer stuff it's often 3vdc, but on older laptops it might be 5vdc or GOK's. But one pin needs to have voltage and time there's the main battery or AC adapter power so pushing the button starts the boot process.
    Crazy old guy with a basement full of Pentium 1 laptops and parts

  6. #26

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    Thanks DeltaDon for your input!

    I did remove the two light blue caps. My eyesight is so bad that I can't really see if they are bulged or not, but
    others on the internet reported that these two were bad on same model laptop. I'm also starting to think that I need to
    start putting back some caps where I have removed suspect ones. And then checking if there is any change.

    I will check RTC voltage, when psu is connected to the mainboard. First thing on monday evening, since I'm out of home for the weekend.

    I kind of believe, that on/off switch is working. When I connect psu to the motherboard, DC IN led stays on, green.
    It does not blink. Only when I press on/off switch, the DC IN blinking will start (one long, three short blinks).
    But, I can still check the voltage for that switch too.

  7. #27

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    Wait... You tried powering it up with missing capacitors?

    No wonder it doesn't work right. They're needed to complete some circuits.

  8. #28

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    Quote Originally Posted by VintageVic View Post
    I did remove the two light blue caps. My eyesight is so bad that I can't really see if they are bulged or not...
    Visual inspection will not reveal 75% of the issues associated with bad caps. IOW, for every bulging cap there are likely three more that do not show any visual signs of being defective.
    PM me if you're looking for 3" or 5" floppy disks. EMail For everything else, Take Another Step

  9. #29

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    Quote Originally Posted by DankEngihn View Post
    Wait... You tried powering it up with missing capacitors?

    No wonder it doesn't work right. They're needed to complete some circuits.
    ahm, a bit shamed to say that that's right.
    I once had shorted tantalum cap in 1541 drive and removing it enabled the drive to boot.
    But, as said in this thread earlier, only tantalums get shorted and that test cannot apply here.

    So, my search for spares starts here.

  10. #30

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    Electrolytic capacitors can fail short as well, usually caused by short but extreme power surges.

    I have a biostar board with caps that look fine, but have completely failed short around the CPU.

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