8" LCDs defective?

(I also emailed Pimoroni support, but thought I would post here in hopes of a quicker solution)

I purchased two 8" LCD kits from Adafruit, this kit here:

I connected one of them to my computer and it worked fine at first. But now it displays nothing but a bunch of vertical lines, no image.

I connected the second display, and it displays a very washed out image that initially was mirrored. I tried swapping the displays, and the issues seem to stick with the display and not the control boards (i.e. the mirrored display is mirrored on either control board, the vertical line display is nothing but lines on either control board). After a bit of component swapping, the mirror displays seems to be unmirrored now, but it is still very washed out and flickering.

I’ve tried reseating the ribbon cables with no luck, and I’m not sure what else I can do to troubleshoot. Is it possible I got a bad batch? I can’t see anything obvious on the control boards, cables, or connectors.

I’ve seen a few very similar posts on this forum and the Adafruit forum from this year, but no obvious resolutions were posted by the authors.

Small update: Pimoroni sent me two replacement kits - one of those displays a similar vertical line mess as one of the previous kits, the other won’t even power on at all.

I can’t imagine what I might be doing wrong, there isn’t much to these things. The ribbon cables are fully seated and aligned, there is no visible damage on anything. I’m stumped :(

The odds of getting several faulty displays seems unlikely. Looking briefly at Adafruit’s docs, like many others relating to driving current hungry displays and boards. I would look towards your power supplies, as a first check. If your supplies cannot provide enough current, you will experience brown outs. This is where the voltage falls below the various processors ability to function and crash. This results in messages and data getting corrupted and the kind of results you describe in display.
Try multiple power supplies with a common ground. So each device has a good supply of power and the ground allows data/signals to have the same ground reference.

That’s a good thought, but the power supplies I am using are the ones recommended by Adafruit which output 2.5A, while the displays require 780mA. Also if it was just a power supply issue, I would think each display would be displaying the same issues - but instead I have four displays that all display unique flavors of “not working right”.

Of the four displays I have, I do have one that is kind of working, but if touch the ribbon cable in just the right way the image cuts out. It doesn’t do this if I try to move the cable around near the connector on the control board (as though it were a bad connection there, which seems like it would be the most obvious culprit). Instead it seems like it’s an issue with perhaps some of the components that are on the mid part of the ribbon between the controller and screen, or a connection inside the screen itself.

Of the four displays that I now have, connecting them to the same control board, with either of the 2.5A power supplies recommended by Adafruit, I have:

  • One display that seems to be working ok although with just the right light touch on the ribbon cable the image cuts out
  • One display that has a washed out white/gray image
  • One display that displays nothing but vertical lines
  • One display that is completely dead, the backlight doesn’t even light up