RE: Bars of squares appearing on bootup
Just had a thought for you. Some people have had problems with their cards reading because their MK3 SD card slots metal shield deforming over time, and someone came up with a fix:
https://www.prusaprinters.org/prints/15388-prusa-mk3-sd-card-slot-fix-not-reading-the-card-at
Obviously you won't be able to print one yet but you might be able to make a temporary one to test whether it is that causing the problem. Find some plastic that is about 1.27mm thick and cut a strip about 43.18mm (slightly under is better) x 25.4, (over is better than under) and slide it in as shown in the video. This could fix it enough for you to be able to print a correct one. If no plastic a stiff card or anything else that's non conductive would do. It just needs to be nice and rigid.
If the existing card works then that is all that is wrong, if it doesn't then get a new card and if that doesn't work I'm afraid you'll need a new LCD board which is (brace yourself....) £51.55 VAT incl., $67.74 VAT incl., 57,15€ VAT incl. direct from Prusa. Hope it's not that for your sake.
RE: Bars of squares appearing on bootup
@3delight
Thanks for dedicating so much time to helping me with these issues, I do have another printer so I should be able to print the piece you linked.
RE: Bars of squares appearing on bootup
You're more than welcome. Great news that you can print that out, at least it will help you with diagnosing the cause! Hope all goes well.