The first screen of Marlin 2.0 is showing some horizontal lines, appearing to be broken We are using the branch bugfix 2.0 and the first screen of Marlin is showing some horizontal lines, appearing to be broken.



After 3 seconds, the boot screen appears and everything works normally.



We have tried to disable the custom bootscreen:

//#define SHOW_CUSTOM_BOOTSCREEN


We have tried to disable the Marlin bootscreen:

//#define SHOW_BOOTSCREEN


We have checked the power supply.

We have wrapped the "flat cable" in aluminum foil and ground everything correctly.

We have deleted the "firmware.bin" and it did not solve the problem.

The first time the firmware is loading the "firmware.bin", those horizontal lines do not appear, but when it is loading the "FIRMWARE.CUR" it does appear.

What exactly is happening? How do I fix those horizontal lines on boot?
Something is causing your screen to get signals to display that before your board properly takes it over after 3 seconds.  It is an oddly repetitive pattern.

If it is software, you should not see it on a stable stock marlin release with minimal customizations to enable the LCD.  Usually nothing else shares pins with the LCD, but please do double check pin assignments.

Beyond software lies a realm of hardware issues:

Issue could be due to bad wiring or wires running in areas where they are picking up noise as the system boots up; LCD ribbons are not particularly noise resistant.  I say wiring but it could be anywhere along the circuit, including circuit boards.

There is also some (smaller) chance that your power supply is providing the noise at the initial boot up in which case you may be able to resolve it by adding capacitors to stabilize the DC voltage.  Not sure what check you already did of the power supply, but a DC (RMS) reading may not show anything strange on a regular multimeter even if there is a strange AC signal.