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Venue 11 Pro travel keyboard - touchpad initialization issue

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Venue 11 Pro travel keyboard - touchpad initialization issue

This question has been answered by eigenmatt

Hi,

I recently bought an Venue 11 Pro 7140 and am having some intermittent issues with the touchpad, similar to issues reported by some others here. Basically:

* If the battery inside the travel keyboard is flat or disconnected, the touchpad works reliably.
* If I keep charge in the keyboard battery, I have intermittent problems with the touchpad not sending any touch events (even though the USB HID part works fine and I can even run the MSP430 firmware update utility).

I probed the 6-pin connector that presumably goes to the touchpad and found the following:

* With the tablet disconnected, the 3.3V rail seems to be floating at around 2.0V.
* After connecting the tablet, it comes up to 3.3V.
* However, pin 3 of that connector is now low whereas it's normally high when the touchpad is working normally.

My battery voltage is about 7.8V so seems to be fine.

I assume that, with the tablet disconnected, either (a) the touchpad is meant to be off and it's being back-powered with 2V through some path, which might be putting it into a bad state, or (b) it's meant to be on and I have a power supply issue.

Before I dig further, does anyone have any more insight based on this data, either via inside information or probing their own unit?

Matt

Verified Answer
  • I managed to fix it in the end, it was a failed transistor in the travel keyboard, specifically the transistor that controls power to the touchpad/keyboard/STM32.

    N.B. for other users: this is only relevant to this specific scenario where the touchpad doesn't work reliably with the battery charged and works reliably with the battery *flat*.  Unless you're certain you know what you're doing you should call Dell tech support.

    Full write up of my troubleshooting here: http://zmatt.net/dell-venue-11-pro-travel-keyboard-troubleshooting/

    Matt

All Replies
  • Hi eigenmatt,

    Thanks for posting.

    Here is some information you may find helpful: http://dell.to/2qQW8qa

  • Hi Robert,

    Thanks for the info. My problem is actually the opposite - the touchpad doesn't work reliably when the battery *is* charged.  The root of the problem is that my touchpad is being powered with ~2V when it should be off (e.g. when not connected to the tablet), which sometimes causes it to end up in a bad state.

    Edit (24/5/2017): my previously posted schematic was incorrect, I'm redoing it and will report back when I have a definite diagnosis.

    Matt

  • If that's the case, please perform a diagnostic check, then contact Tech Support for further assistance.  Thanks.

  • I managed to fix it in the end, it was a failed transistor in the travel keyboard, specifically the transistor that controls power to the touchpad/keyboard/STM32.

    N.B. for other users: this is only relevant to this specific scenario where the touchpad doesn't work reliably with the battery charged and works reliably with the battery *flat*.  Unless you're certain you know what you're doing you should call Dell tech support.

    Full write up of my troubleshooting here: http://zmatt.net/dell-venue-11-pro-travel-keyboard-troubleshooting/

    Matt