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?
Solved! Go to Solution.
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.
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/