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  1. #1
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    wacom repair

    Following considerations deal with a broken Wacom Intuos3 A4 (9x12) tablet and the steps I took to repair it. The problem it had was that once connected to the usb of my computer, apple/windows did request for drivers but once these were installed the tablet did not show any further response.

    The tablet was sold as non-working and I decided to get my fingers dirty. What was broken exactly was at that time unclear. Although the operating system as described above would recognize the tablet, install drivers and indicators at the tablet showed some light, I measured no function at all at the scan lines or any buttons whatsoever.

    When the device arrived, I spend some time on it initially. My first suspicion was focused on possible defective onboard power supply circuit. Because I did not have any documentation or reference device, this was hard to check. I would need at least a second device for reference measurements.

    Since then several months went by, when I finally found an affordable Intuos 3 tablet. Although it was the smaller A5 model, the larger A4 model is electrically almost identical. Both the A4 and the A5 tablet use the same layout for the power supply circuit, use the same cpu (Mitsubishi, M30240, M16C family) and some undocumented Wacom IC's like a W4023F (See EP0967566 Patent info).

    In order to ease the drawing of a circuit diagram from the power supply part, I scanned the PCB and uncovered its tracks. From this, following image was created:




    The power supply circuit generates three different voltages. The power supply circuit is turned on and off with control pin 40 from the cpu. To get the cpu itself operational, the +5V usb is connected directly to the cpu. A simple measurement already revealed the broken tablet did not enable the power supply circuit for some reason. However manually enabling the power supply circuit, by isolating pin 40, and connecting the control line to gnd, showed the power supply was functional as well at the broken tablet. I noticed a small difference between the A4 and A5 model, that one of the voltage regulators at the A4 tablet produced 5.0V instead of 3.3V. But because its markings were different and corresponded to its voltage, this should be no problem.

    I realized now I had come that far where I actually had taken all steps which I wanted to investigate initially. To get any further I first needed to be sure the cpu wasn't broken at the A4 tablet. So I swapped the cpu's between the A4 and A5 tablet (I used quickchip to prevent damage). Once accomplished both tablets did not show any change in behavior: the A4 tablet was still not working, and the A5 tablet was still operational. This indicated both cpu's were functional. Another component which was also powered from the +5v usb, was a 93C46 eeprom. Exchanging this part along both boards did not change anything either. Because I was unsure whether model specific data was stored into the eeprom, I exchanged both eeproms once again, reverting them to their original location.

    Further measuring and comparing voltages and control lines around the cpu between both boards didn't result into some abnormality. Just to be really sure, I exchanged also the W4023F custom chip, with no change either. From the overall picture I had now, the most likely presumption would be the device did not manage to initialize completely from a software point of view and as a result of that the it would not reach the point where it could enable the power supply circuit. So I had to find more sources which prohibited the cpu to get initialized. Also other components which did not receive power directly from the +5v usb could be excluded. The few components around the cpu were fine, but my attention fell again on the 93C46 eeprom. Although I had done some inspection before at the eeprom, I started now to measure with the oscilloscope at each pin and checked activity during plugging-in of the usb connector. By comparing the measurement with the working A5 tablet, I finally found the problem: one of the pcb tracks, connected between pin 23 of the cpu and pin 2 of the eeprom was open (caused by a bad via?). Connecting a by-pass wire, and replugging the usb connector, made the device to immediately start working.

    Update: after 3 months I found what had caused the bad connection at the pcb track. (In fact there were a few more). I found some left-overs of a sugar/coffee mix, which had been completely dried out. The previous owner must have spilled some of his drink into his tablet, which caused corrosion.

    See the attached pdf schematics which I reverse engineered for further reference.

    •   Alt5th February 2008, 00:50

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  2. #2
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    Re: Wacom Intuos3 repair success, schematics

    Very thorough, impressive. But how did you separate the pcm from the gray hull element? I found the adhesive to be quite strong and did not want to risk breaking the pcb.



    •   Alt25th November 2009, 21:43

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  3. #3
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    Re: Wacom Intuos3 repair success, schematics

    Really impressive work Mozart!

    It's been really usefull your reverse engineering!

    I've followed your steps, and my problem seems to be different. When plugged to usb, it blinks for a second the blue light, but then it falls back to off.

    My power supply goes for 5v on TR001, but then it goes off for all others TR00#! althought i get 5V on CPU 40 pin... Any thoughts? help? seems my intuos 3 9x12 has also some small spot wear off on track 3 that runs on f03.

    Much appreciated.


    PD: By the way, the easiest way to remove the bump-stickers for me has been to gently open the case and while midopen apply a cut to help it open.



    •   Alt3rd July 2013, 00:00

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  4. #4
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    Re: Wacom Intuos3 repair success, schematics

    @chewe. My tablet intuos3 has the same problem with the blue light blinking for a second when plugged in to usb. and then turns off. Did you find a sollution?

    much appreciated

    Cheers



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