Sounds like some sort of intermittent issue.
If diags is reporting an error, there is still a problem.
Since it sounds like it works some of the time, here are some likely possibilities:
-
wiring issue
This could be anything like a loose wire or improper solder joint, using wires that are too long,
to an actual mis-connected wire.
In particular, what is the glcd modules reset pin (glcd module pin 14) connected to?
Some glcd modules are very picky about the reset signal. -
bad or insufficient power.
Can you measure the voltage between pin 1 and pin 2 of the glcd module?
Is everything powered from the same power supply? -
bad glcd module.
This tends to be quite rare but it does happen.
Was the glcd module ever mis wired and powered up? even briefly?
Can you post some clear photos of your setup with closeups of the solder connections
on the glcd and a photo that clearly shows all the wires and their connections?
--- bill