LS1028A random screen tearing/flashing [resolved]

The LS1028A based Reform just came.

I booted the pre-installed SD card which has Debian GNU/Linux in console mode on it.

The screen would randomly flash/display garbage, especially in the top left part.

The screen cable connection is very awkward with the eDP adapter so it may very well be mechanical problem.

Anyone else seeing this?

Yes, this is a known problem and related to shielding/interference with the flat eDP cable. Here is a video that shows the effect of different positions of a flat ferrite ring around the cable:

This is the one that was used in the video if I’m not mistaken:

But there is a much simpler solution which is to just surround part of the cable with tape:

The tape in the photo is this one but other kinds of tape should work just as well:

On IRC Lukas said:

it looks like the most important thing is that the cable doesn’t hug the hatsink nor the module too much. my theory is that it is about ground plane discontinuity

Thanks for the reply. There is already something on the cable covered by black tape so it’s possibly a pre-installed ferite.

Then I guess @mntmn will be the person who will be able to solve your problem. :smiley:


I’m very sorry that you are experiencing this issue. The real fix is the photo that josch posted above, with the yellow tape. Unfortunately we figured this out only after going with the ferrite solution, which turned out to be a red herring. The ferrite just made the FPC cable sit in a better position mechanically between the heatsink and module.

The real solution appears to be taping around the section of the FPC cable that is between module and heatsink (after the folded portion), because this will keep the cable a millimeter away from the heatsink and module. My theory is that this prevents the heatsink to become a ground plane for the differential signals that then abruptly ends where the cable exits the heatsink area.

In the meantime we have also respun the eDP adapter so that we can use a different cable that does not need the origami to flip it around. If you don’t want to try to apply the tape solution, please contact and we will send you the new adapter + with tape preapplied.

Thanks for your reply.

I will look for something that can be applied to the cable to keep it from touching the heatsink first.

Adding some tape around the cable indeed seems to resolve this problem.

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