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Thread: Toshiba T1200 schematic

  1. #11

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    Quote Originally Posted by rimmeruk View Post
    The blinking red light is the battery charging circuit protection, the battery needs to be functional and chargeble along with the DC input power.
    If you have missed any caps on the board then you may also get the blinking red light. You could say anything which does not power on
    has a design flaw, I wouldn't say it was a flaw as it works with all the correct capacitors and batteries replaced.

    I've repaired 2 units with the blinking red light and the blinking led that you are talking has other conditions in which it blinks to show
    the diagnostic code. There is also an led code output on the LPT port which are all listed in the repair manual with the correct procedure
    to remedy the fault. I guess that you did not use an LPT diagnostic connector on the LPT port as the blinking red led suggests there was a fault
    code available and the error could be something other than the battery or power.

    You see, almost all Toshiba laptops from that era had an integrated diagnostic circuit and ROM which allowed the use of a LPT dongle to diagnose
    any faults with the system through the printer port (of course you'd be stuck if the LPT port failed). These dongles are easily made with just a handful
    of leds and some wiring. I have used the for all sorts of diagnostics on Toshiba's and you can even reset the CMOS chip and any registered passwords.
    If you are serious about repairing and restoring vintage computers, you would have one of these dongles.

    I guess you were lucky to find 6 working laptops, that's not to say the non working Toshiba's had design flaws is it.
    Thinking about it, you could say that all electronics from that era had design flaws when you compare them to the advancement
    in electronics today

    I'm only trying to point out that you may have missed something else when diagnosing the board and you may have focused all your
    attention to the power supply when the fault could of been something as simple as a jumper switch or corrupt CMOS memory.

    Sorry for the lenghty post, but I always like to detail my response with as much information backing up my statements rather than
    one-shot comments.

    What has it got to do with a Zenith center-negative plug ?

    That's interesting about the post codes. Didn't know the Toshibas had that. I knew machines like the IBM PS/2 did though. And yes, I replaced ALL of the capacitors with brand-new, name-brand components. None were missed.


    I did not use an LPT code reader, but I DO have one, so lets not assume things here. I am very serious about repairing vintage computers and have restored many.


    I actually wasn't lucky at all with the Compaqs. The Compaq SLT is a very well-engineered machine. You don't just get lucky six separate times on one type of vintage computer. If you get six units all from different places and they all work, it's a damn good machine. Period.


    Let me be very clear about one other thing too: the Toshibas were not my first rodeo. They are far from it, in fact. I am not a newbie. I don't consider myself an "expert" by any means and never will, but I do know a little bit about vintage computers.


    Some of the systems I have repaired include the two Compaq LTEs that had capacitor damage, which required me to hunt and repair broken traces with a magnifier and a multimeter. They are fully-working now, and have been for over a year (see this thread about them: http://www.vcfed.org/forum/showthrea...E-8086-repairs). Or the Compaq Portable I spent about a week diagnosing the dead CRT on, which, after swapping some parts around and looking over the schematic for a while, I determined was the horizontal output transistor, which I replaced, and the CRT worked fine afterwards.


    That being said, I'm not saying there is no way the Toshibas I have couldn't be fixed by anyone, I'm saying the issue was NOT just the caps, as they have ALL been replaced and the machine still doesn't work. I also cleaned the PSU board VERY well.


    Pretty sure I mentioned this above in another post, but I will say it again: I have seen several other cases of people replacing the caps in these early (pre-386 era) Toshiba laptops and it not fixing the issue. I'm not the only one.


    And I'm sticking to it about the design of these being flakey. I have worked on/repaired/recapped lots of vintage PCs/Macs and I have never seen anything as temperamental as these early Toshibas (just the early ones, 386 and later units seem to be very reliable). Hell, I successfully restored a Macintosh Portable even (one of the most temperamental Macs ever). But these Toshibas are something else, that's for sure.


    And another thing, I have nothing against Toshiba, I've got a T3100e, 2 T5200s (gray AC-powered plasma models, very reliable) and some newer 486 and Pentium models (like a Libretto 50CT among others), and they are all great. Some of the better machines I have actually. But their early battery-powered machines just aren't reliable enough to warrant me owning them.


    About the Zenith, I'm pretty sure you mentioned Zenith's odd power supplies above. That's what I'm talking about.
    Compaq - “It simply works better”

  2. #12
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    Quote Originally Posted by compaqportableplus View Post
    I actually wasn't lucky at all with the Compaqs. The Compaq SLT is a very well-engineered machine.You don't just get lucky six separate times on one type of vintage computer. If you get six units all from different places and they all work, it's a damn good machine. Period.
    But maybe all six were repaired under warranty and/or repaired subsequently.

  3. #13

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    Quote Originally Posted by modem7 View Post
    But maybe all six were repaired under warranty and/or repaired subsequently.
    Some of them have had the hard drives replaced and memory upgraded, but beyond that, they don’t appear to have had much else done to them. These machines don’t break much even at 30-plus-years of age, so I’d say it’s unlikely all 6 of mine had major failures back in the day. That’s not to say an SLT never broke, obviously anything can happen, but they aren’t trouble prone by any means.
    Compaq - “It simply works better”

  4. #14

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    Quote Originally Posted by compaqportableplus View Post
    Some of them have had the hard drives replaced and memory upgraded, but beyond that, they don’t appear to have had much else done to them. These machines don’t break much even at 30-plus-years of age, so I’d say it’s unlikely all 6 of mine had major failures back in the day. That’s not to say an SLT never broke, obviously anything can happen, but they aren’t trouble prone by any means.
    Also, all six were from different purchases. I didn't buy them in a lot from the same place or anything. Sorry if I didn't make that clear.
    Compaq - “It simply works better”

  5. #15

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    You'd be surprised how missing a single SMD tantalum capacitor can prevent the machine from powering up or functioning correctly.
    The Toshiba T1200 has many small SMD tantalum caps that leak but also don't show any external signs of failure. It's not just the
    obvious electrolytic caps that should be replaced.

    As for the vintage 386/486 Compaq's, I agree they are great machines, but just as likely to have the same issues. I've repaired many
    Compaq, Toshiba's, Dell, IBM etc.. and some are more favourable to work on than others. Compaq are very easy to dissasembe and access
    the mainboard, so too some Toshiba's, esp the T1000/T1200 series. Compaq made their machines more accessable more than any other
    manufacturer laptop I've worked on. Compaq do seem to have a alot of screen failures or issues with the display.
    The T3000/T5000 series are a figgin nightmare of a machine, I've had 2 units arrive to me and I quickly sold them on, it was like dissmantling a tank.

    Yes, I've read some of your posts and your photos with descriptions have helped me with some of my repairs and I thank you for that.
    Sometimes, these old vintage micros can be hiding a very simple repair, that even the most knowlegable electronics guy could overlook.
    I spent days on one particular machine, that would just refuse to boot or power up. Turned out to be a corrupt CMOS memory
    chip. There was even 2 jumper pads on the board with it silk screened to reset the CMOS chip. I had to place a solder blob over the
    pads and power on. I was just kicking myself when it finally booted with just a CMOS error. Sometimes removing the batteres does not always
    reset a CMOS chip and many chips have external pads for jumpering to do this.

    Just something to take into account when working on these machines, it is not always the caps that prevent them from powering up.
    The BIOS/CMOS is the first call from the CPU and if that comunication fails then some machines will fail to boot. Still, all the caps
    should be replace as a matter of course, as they too are integral to the correct operation of all the components and power supply.
    Last edited by rimmeruk; September 22nd, 2020 at 12:40 PM.

  6. #16

    Default Toshiba T1200 Power Board

    Here is a photo of the main power board for the Toshiba T1200.
    All of those elctrolytic caps must be replaced and I have also highlighted 2 SMD tantulum caps which
    also must be replaced. The large one is 10uF 16V and the smaller one is 3.3uF 16V. You can use standard
    electrolytic caps to replace the SMD tantalum's, if your OCD will allow that Just shorten and bend the legs
    into an L-shape and solder to the pads.

    I don't use hot-air guns to remove SMD caps, usually when they leak they are very easy to gently twist and pull
    away if you heat one side with an iron. The round SMD caps are very easy to remove without any heat by gripping
    them with some long-nose pliars and gently twisting them off in a circular motion. I very rarely rip the pads
    using this process if I'm careful enough. In fact, using hot-air on SMD caps will cause the pads to lift.
    The board can then be cleaned with IA and the pads re-tinned with some solder.
    Attached Images Attached Images
    Last edited by rimmeruk; September 22nd, 2020 at 01:02 PM.

  7. #17

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    rimmeruk,

    There was one cracked tantalum cap on the 1200’s PSU board I replaced and I did check the other and it seemed fine, but maybe it isn’t.


    And yes, I agree that things can get overlooked quite easily. I’ve done it many times and still do occasionally.


    Also, something I want to reiterate; I was in no way claiming above that a Compaq has never broken and that they are 100% immune to problems, that would be silly, but I can genuinely say that I have never had a major issue with any SLT and I have had one of them for almost 10 years now. Again, not to say one could never malfunction, but they are definitely more reliable than some of the others.


    And another thing I want to reiterate, I’m in no way saying I am the “best” at repairing vintage computers, and I hate arrogant people that feel that way. There are many people on this forum and elsewhere that are far more experienced than I. I’m always eager to hear advice from other people that repair this stuff. The only point I was making above is that I have fixed a few of these things before.


    I am very happy to hear some of my posts have helped you.


    Thanks for that photo. I did have a chip unsoldered from the PSU board in that machine though, so I’d have to dig those parts back up and reinstall that chip to do any testing.
    Compaq - “It simply works better”

  8. #18

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    You're welcome, I don't believe anyone or claims to be an expert

    There are even more SMD caps on the main logic board to replace, it's a pain in the ass job when you start, but the reward is worth it guess.

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