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Thread: My Toshiba T1100 Repair

  1. #1
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    Lightbulb My Toshiba T1100 Repair

    I'm opening this to share my adventures in repairing a T1200 Toshiba, circa 1984



    I wish the alreadi thanks Modem7 for his great Toshiba ressources on minuszerodegrees.net





    I'm very happy with the exterior condition of the unit.
    I also have what seems to be a VERY rare modem/RTC/rs232 optional card.


    When all goes well, here's what you can see:






    I'll first describe my battery replacement ( in the next messages ), then other repairs.

  2. #2

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    Very nice machine!!
    I wait for future post about repairs!

  3. #3
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    This is obviously a T1100 (not plus) and not a T1200 as I put in the massage body but it seems I can't edit.

    Step 1 )

    Batteries !

    What I got with it looked like a 1992 replacement, this was not a 1984 battery, but it's not something someone has built in hosue either. I guess they put tape on it to avoid rattling.




    Batteries where in a sorry state to say the least (1992 at best)




    I bought equivalent batteries in Poland, where NICD are still in stock (don't ask me why) despite beeing forbidden in europe since 2006.



    Soldered them



    I also recycled the original 2x5A fuse ( which would make it a 10A fuse).



    Battery I created looks as good if not better then the original from toshiba

    One thing that was really difficult was to recycle the original cables (which I did) because they were oxidized even inside the plastic, in the while length ! Never saw something like that. I really struggled to solder them back, after cutting 10cm out of them.

    Strangely enough; 100% fully charged this delivers 14V (on an empty load) instead of 12V. It works anyway and is within the Toshiba specs (+/- 20%).

  4. #4
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    Issues i've got

    - the freaking "B" key does not work. I tested with a multimeter and contact does not happen at all when you press it.
    I plan to unsolder the $/pounds key and swap them, as i'll never type "uk pounds" on this laptop.

    - I have to power it on at least 10 times to get it to boot. This is a real issue for me.
    I could blindly "recap" all the electrolytics and hope for the best ; but they don't seem leaky, the one i've unsoldered "as a test" is perfect in an ESR meter, and i'd like to get a real diagnosis. I'm poking around with the oscilloscope.
    So for all I can tell is that plugging in the screen provokes a 3A current spike at boot, which doesn't happen with cd screen unplugged, and I find this very weird. All voltages are correct (+12v,+5v,-5v,-12v) and all within tolerance. It's difficult to make measurement with the laptop running because it has to have the lid cloded to have keyboard & screen. This makes debugging a PitA.

  5. #5
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    Quote Originally Posted by CedsRepair View Post
    I have to power it on at least 10 times to get it to boot. This is a real issue for me.
    For readers, is this intermittent 'boot' failure: 'nothing appearing on screen' or 'will not boot from diskette' ?

    Quote Originally Posted by CedsRepair View Post
    I could blindly "recap" all the electrolytics and hope for the best ; but they don't seem leaky, ...
    The vast majority of faulty aluminium electrolytic capacitors that I have encountered, showed no visible signs of failure.

    Quote Originally Posted by CedsRepair View Post
    ... the one i've unsoldered "as a test" is perfect in an ESR meter,
    The primary property of a capacitor is capacitance. If I was measuring an aluminium electrolytic capacitor, capacitance would be my first measurement (measured out-of-circuit), and then I would measure ESR (which is a crude measurement).

    And for any in-circuit ESR measurements, I would be watching out for capacitors wired in parallel, something that would compromise an ESR measurement.

    Quote Originally Posted by CedsRepair View Post
    It's difficult to make measurement with the laptop running because it has to have the lid cloded to have keyboard & screen. This makes debugging a PitA.
    Your "it has to have the lid cloded to have keyboard & screen" has me confused. If the lid is closed, the keyboard cannot be accessed, and the screen cannot be seen. Maybe you meant partially closed.

    Quote Originally Posted by CedsRepair View Post
    So for all I can tell is that plugging in the screen provokes a 3A current spike at boot, which doesn't happen with cd screen unplugged, and I find this very weird.
    I do not see 3A peak at power on time of either of my two T1100's. It is about 500 mA peak (measured using the min/max mode of my Fluke multimeter).

    My T1100's can power up and boot to DOS from a (720K) boot diskette when the display unit is unplugged from the mainboard. I can tell that by:

    * About 35 seconds after turn on, I hear a beep from the speaker (if fitted), then I see the access LED on the front of the diskette drive turn on; then

    * Once I am sure that the DOS boot from diskette has finished, I will hear the speaker beep whenever I enter the following DOS command: echo ^G con
    (The '^G' bit is done by holding down the CTRL key and then pressing the G key.)
    (Of course, the DOS command could optionally be put into an AUTOEXEC.BAT on the boot diskette.)


    BTW: If your T1100's speaker is missing, a speaker gets connected to connector PJ1 on the mainboard.

    BTW: On both of my T1100's, I am yet again seeing poor power connection to the floppy drive. The connector (shown [here]) is very loose, and the poor connection stops the drive from working. Need to permanently resolve.

  6. #6
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    The boot failure/success ratio is currently 9 misses for 1 boot.

    On a full battery, I switch the power button, the screen "blinks" (you can see the pixels lighning up if you put contrats to 100%)
    It often briefly displays two horizontal lines while I power cycle.

    Then nothing happens.
    No memory count/test, no beep; nothing. Also, no error code on LPT (I checked)
    I can leave it like that 5 mins, nothing will ever happen.

    With an oscilloscope but without the top cover ( so keyboard + screen removed) all I can see is :
    - All voltage rails are OK ( good voltage + no ripple )
    - The CPU gets a good 4,77 Mhz clock on it's clock pin.

    I've got this behaviour both on "LCD" setting, but also on CRT setting. (And with or without the keyboard+screen.)

    Basically something crucial fails to power up,
    I suspect the "bus controller" which got a tiny little bit of corrosion out of the old battery, but the rest of the motherboard looks tidy.

    I could (as many people do) "recap" the power stage but again, I see nothing wrong with the voltages. Could they have leaky/faulty caps while outputting the perfect voltage they're supposed to ?

    Hope this clarifies and really thanks again for your time on this,
    (forgive me if my english sounds weird, not a native speaker, also the fact the forum doesn't allow me to edit my previous messages does not help)

  7. #7
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    Quote Originally Posted by CedsRepair View Post
    ... also the fact the forum doesn't allow me to edit my previous messages does not help)
    In a way, that is good. E.g. Since a particular thread started a month ago, I have been reading new posts as they have appeared. The post count in that thread is now at 50, and the last post that I read was #47. All I should need to do now is read posts #48, #49, and #50. I should not need to also re-read the previous 47 posts because of the possibility that someone may have added/altered information in one of those posts.

    But there is some time-limited post editing ability. For example, 30 minutes ago, I made a post to a thread. Right now, I still see an 'Edit Post' option (to the left of the 'Reply' option) for that post, but I know that sometime later, my 'Edit Post' option for that post will disappear.

  8. #8
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    Quote Originally Posted by CedsRepair View Post
    With an oscilloscope but without the top cover ( so keyboard + screen removed) all I can see is :
    - All voltage rails are OK ( good voltage + no ripple )
    ...
    So you have eliminated the possibility that your 3A (peak) drawing display unit is causing power instability at start-up time (the time period that it is drawing 3A).

    Quote Originally Posted by CedsRepair View Post
    ... so keyboard + screen removed ...
    In case the information is useful to someone later, the diskette drive is not required either. With no display unit, no keyboard, no diskette drive, and no option card plugged into my good T1100 mainboard, the POST issues a single beep about 35 seconds after I turn on the power switch.

  9. #9
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    Quote Originally Posted by modem7 View Post
    ... the POST issues a single beep about 35 seconds after I turn on the power switch.
    About 18 seconds for 256 KB of RAM (i.e. that soldered to mainboard).
    About 35 seconds if an additional 256 KB is added via the plug-in module.

  10. #10
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    In my case removing the floppy did not help.

    So even without screen, keyboard, floppy : no post beep. (Well : once every now and then)

    I'm really a bit out of options. Voltage rails seem fine, unless a very short transient at boot time causes an issue (that is not to be ruled out)

    Battery is as charged as can be (it's new). Motherboard looks OK. I tested one of the big 470uF caps of the dc-dc converters, out of circuit, and they are ok on esr & capacitance.

    I feel i'm so close to find the solution and yet, i'm not making much progress.

    Really the issue here is that my problem doesn't seem to be a power problem.
    And the 80c88 CPU get's it's clock. (that's as much as I can tell with an oscilloscope)

    So what is the actual boot process of the thing would help investigate a bit.
    I'm still feeling that this is related to the bus controller. (the chip in the middle of the motherboard)...
    I cleaned it at least 5 times...

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