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Commodore C286-LT/C386SX-LT - verschiedene Probleme

    Ok, now are all capacitors on the power supply unit and the Display PCB are changed.


    Please check if the are some more capacitors on the mainboard which are may be faulty because the display circuit has to get the signal Information from the integrated graphics card on the mainboard. This could be also the cause.


    May be the Mainboard uses this critical capacitors for other functions.


    Otherwise it will be more difficult to find the failure because you have to check the display PCB circuit in more Detail.

    Please be Aware that defect capacitors can leak but must not. A leaking capacitor is only one indicator for a defect capacitor. Also it is possible that a capacitor could have lost capacity but it has not to blow or leak. This is than only to detect by measuring the capacitor.


    Goid luck again to find the root cause.

    Good evening,
    it's my first time and first question here.


    Seems that I am also faced with the same error and symptoms regarding the display issue(s) as shown in this thread:


    Commodore C286-LT/C386SX-LT - verschiedene Probleme






    The only difference is that I am working on getting this solved for one C286-LT and one Sanyo MBC-17NB.
    Both machines seem to be build up similar including Power Supply , Mainboard, Screen, etc. .


    I had already changed all electrolytic capacitors on the internal Power Supply and on the Mainboard of the C286-LT.
    After having done that the C286-LT worked for ca. 20 minutes without the mentioned error.
    Suddenly the same error occurred again and did not disappear.
    I checked all connectors and penetrated all components with heater and cooling-spray without any effect.


    So maybe the problem was solved by anyone here or does someone have any new idea/input.


    Thanks a lot for your attention

    Hi Schmitti,
    thanks for your feedback - I already did the PCB check several times.
    Means heating, cooling and physical pressure but no reaction or change was shown.


    I am confused since the LCD-problem appeared in a minor extent before changing all capacitors.
    After changing them the effect disappeared for ca. 20 minutes and suddenly came back.


    So I thought that some components were killed by the original external power supply again.
    Checking all changed components again did not show any fault.
    Therefore I did an "injection" with an external switching power supply for the required operating voltage(s) to be sure.
    Unfortunately no improvement and still the same error.


    So I think it would make sense to use an oscilloscope to check the VGA and sync signals but I don't have the corresponding circuit diagram.


    By the way , if you prefer to communicate in German - no problem


    Thanks

    Ok I see you have done many checks and has done them partly repeated already.


    Do you have checked that all changed capacitors have the same capacity as the original capacitors?
    Do you have already checked if an old original capacitor has damaged some lines on the PCB board?


    This are currently the first topic of my thought.

    Hi,
    thanks for your further thoughts and input.


    Yes, I have re-checked the capacitors and inspected the lines on the PCB.
    I could not find any damaged line or wrong capacitor.
    I think to check the coils, transistors and voltage regulators on the internal power supply.


    Any idea is welcome

    At the beginning you wrote you have an Commodore Laptop and one from Sanyo. These should be nearly the same. Is it possible to use the Sanyo power supply for the Commodore Laptop and in the opposite?
    If yes, does the failure behaviour will Change (a little)?


    Do you have an oscilloscope? If yes, then it would be more easy to check the Output of the power supply with load. But the Laptops has internal an second supply which will Change the Output of the external power supply to the internal used voltages.
    So the internal different voltages have checked all too.


    If you have only an multimeter this not easy to check them because some possible Event are not be able to check with a multimeter only.


    If you have here a measured result please write them.

    Hi Schmitti,
    thanks for your answer.
    Meanwhile I was able to determine that the problem is not based on the Mainboard or Power Supply by simply exchanging the dsplays between Sanyo and Commodore.


    After opening the frame of the faulty Display I could see some coils , capacitors and a little transformer.
    The little transformer seems to produce high voltage for the Cold Cathode Fluorescent Lamp.
    I also could see a high voltage ceramic capacitor with 4.5 KV.
    First inspection will be to change the elektrolyt-capacitors and to check the low voltage signal with the osci.
    The high voltage ceramic capacitor with 4.5 KV is not available in any electronic-store.


    So let' see...

    Hi Schmitti,
    thank you, my last approach was wrong , the ceramic capacitor was not faulty I checked it with a special probe.
    Finally I deactivated the Cold Cathode Fluorescent Lamp circuit completely and the display error was still there.
    After isolating the error-source step by step with osci and multimeter based on signal/voltage comparison I could identify one of
    the 16 OKIM5299B LCD Segment drivers (80 pin layout) on the LCD backplane as final root cause.

    Unfortunately this chip is out of production and I couldn't find any replacement so far.
    So waiting for another idea.

    Perfect, excellent work to identify the bad IC. I have looked for the datasheet of the Oki IC M5229B and found that the file is named msm5229a.pdf for the A version of this IC. But I found the file not. After a longer time I found the B version here:
    https://pdf1.alldatasheet.com/…w/11203/OKI/MSM5299B.html


    May be you can find the IC here:
    - https://www.brokerforum.com/co…arts/OKI/M5299B-eR-en.jsa
    - http://elcodis.com/parts/6363195/M5299B.html
    - https://www.hkinventory.com/p/d/M5299B.htm


    Or an other possibility is to look for old LCD (laptop) Monitors.


    I hope you will have luck to find one IC.

    The faulty display-driver-IC seems to be only a victim of a defective HV-Inverter-Board and/or bad/faulty grounding of this HV-Inverter-Board.

    The HV-Inverter-Board produces the High-Voltage for the display background Cold-Cathode fluorescent lamps (CCFL).


    These inverters are known to get faulty and produce too high voltage peaks which tend to "search" for some way to discharge to ground, like lightning in nature.


    So there are 2 ways to solve this rootcause:


    - modify the display to use LED-Background lighting.

    - use plastic foil and/or hot glue to enforce isolation between the HV-Inverter-Board and all other parts nearby, especially Display-PCB, -Frame or the wiring to the display. Also check for good grounding of the display at the mainboard or internal PSU.


    But this will NOT repair a already defective display! But the other way round: if you just exchange the display(-pcb), the fault will come back soon!


    The fault is starting with -maybe non fatal- discharges at high humidity environments or just appearing sporadic.

    But sooner or later it will destroy some of the electronics, mostly on the display-PCB but also i ve seen completely defective mainboards including even connected HDDs!


    This kind of fault is common to most of the Notebook/Laptop computers of the late 80ties up to about 2010, when LED-Background finally was introduced in mass production.


    Today there are several kits available on the electronic marketplaces to make it very simple to exchange CCFL. Most HV-Inverters work with 12V DC, as also most of the LED-Kits do, so it is rather easy to do this mod.


    With C286-LT/C386SX-LT and NB17/18 the Inverter has the following Pinout (at CN11, which is located on the very upper right end of the main pcb (seen from normal user Position in front of the computer, also this place is available after removing Accupack and small slider door for CMOS-Battery):


    1 GND (switched at the mainboard to enable Software controlled OFF)

    2 +12V

    3 VR

    4 VR2


    VR and VR2 are on the mainboard connected to both ends of an 5k variable resistor (poti) which is labeled brightness ;-)
    So you can use the original brightness control also for analog dimming, if the new LED-Controller has this feature!


    I was working at the early 1990ties for the OEM producing the Commodore Cx86-LT notebooks and some almost compatible "sibblings".



    Start of Ad-block:


    I am planning to reproduce the 2MB RAM Addon-PCBs and also some other nice stuff like 486SLC(2) CPU Upgrades (even for the 286 machines!) and a solution for up to 8 MB RAM (instead of 5MB total reachable via two of above extensions).


    Also a second COM-Port and external Keyboard-connector for using external AT/PS2-Keyboards AND serial mouse at the same time as any other serial stuff like car-diagostic, modem, embedded board programmers is available!


    Last but not least i can offer repair or exchange-/spare-parts for this kind of computer including the external PSU, which is rather bulky, but also unreliable (if not modified), but MUST be used if you want the machine to run and charge NiCD batteries

    (for "mains only" ANY 15/16V 3A Supply will do (correctly wired to the original Mini-DIN connector-cable of cause...)


    All these activities are hobbyist activities, the aim is to keep those pretty little machines alive!


    PN if interested!:)

    Hi RetroVictim.


    Remember to never give up !! :thumbsup:


    Below are photos from the repair of my display.


    1) Broken display:


    Brak opisu.


    2) Desoldered M5299B chips (3 pieces):


    Brak opisu.


    3) Display after assembly:


    https://scontent-waw1-1.xx.fbcdn.net/v/t1.15752-9/167572678_292524688919361_6463146465615492443_n.jpg?_nc_cat=101&ccb=1-3&_nc_sid=ae9488&_nc_ohc=mMenb8IwPucAX905TdN&_nc_ht=scontent-waw1-1.xx&oh=3579a070c635c01ae37ccd4a8fead5dc&oe=6092C58B



    I bought new chips here:

    https://pl.aliexpress.com/item…042311.0.0.528f5c0fOpqnVY


    I did not use any tools to find broken chips. They were very hot compared to the rest and this is how i found the broken ones.


    Now I can think on mods suggested by Roby1111 :D


    The problem I have right now is that I only have 1MB of memory. I also would like to do my own memory extensions but I had to find memory chips M5M44400J first...


    Best Regards