Bad touch digitizer ground connection?


The first thing I noticed was that the touch digitizer becomes completely unresponsive if the phone is laid on certain surfaces (specially my bed and my desk). Touching the metal frame of the phone fixes this issue until I let go.
Then I noticed some ghost touches happening around the center of the screen.
I’ve been doing some hobby work with tiny electronics in the past, and this specific issue has occurred to me before in a bit of a “lab setup” where I didn’t ground the touch digitizer correctly.
I haven’t opened up my phone just yet in case this is a known issue with a known (potentially software?) fix and I’d rather avoid ripping some delicate ribbon cable or something in the process.

Does anyone have an idea? Any known solutions?
Or should I just go ahead, check the connectors or maybe do some probing to figure this out myself?


Hello. I think that could very well be it. Regarding the ghost touches, you can look through comments in this thread: Ghost inputs on FP4



I’m doubtful. The display is all built by DJN. It communicates via i2c and SPI on a flex cable to the main board. The touch is done within the LCD cells and a chip controls both mounted on a flex PCB inside the backside of the display.

The issue with sensitivity I believe did not appear until Fairphone pushed a mitigation that reduced the sensitivity of the screen. This mitigation reduces the length of a ghost touch spaz out and maybe frequency but did not solve the issue. In my experience it’s a bad mitigation as it doesn’t solve the issue and also makes the screen way less usable.

I would get rid of the FP4 and buy a FP5 if you really want to use their products.

It’s not really the sensitivity that’s the issue, the sensitivity is actually fine Imo. I’m on a custom ROM though so I don’t know if that fix is applied there.
The “issue” is complete unresponsiveness when laid on certain surfaces that are well isolated from earth.
It’s not really an issue for me, I just pick up the phone and then it works but it’s certainly interesting and I’d like to know more.

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The “sensitivity” issue solved by attaching a cable (no need to charge) or touching the frame with a finger, was introduced by the software " fix" for the ghost touches. Whatever they did, we dont know and they dont explain this or if there is any intention to fix the new bug. Maybe the CustomROM developer can explain what they did and what is causing this? Because yes the ghost touch “fix” is implemented in CustomROM as far as I know.


yvmuell’s post explains better what I was getting at. What you are complaining about is a side effect of the software mitigation that fairphone implemented.

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