Two rows of white squares on my LCD 2004

[Scintilla]

Hello Everyone,
I thought I would share the problem I've been having with several a 'upgraded' RUMBA and TANGO Arduino PCBs running with Windows 10. I hope it might stir some memories of similar experiences and be of general help. It seems to be a very common fault.
I have scoured the web, and this fine forum as usual, but so far I have drawn a blank.

The problem(s):
I have the LCD 2004 display correctly plugged into the EXP1 and EXP2 connectors, I connect the USB with the PCB jumper in the USB power mode and the display presents the usual characters as expected. At first...

I shut down my PC and, on returning the next day, I'm the proud owner of the 20 white blocks on rows 1 and 3. The LCD display is completely unresponsive to all inputs.

On reinstalling my old RAMPS 1.4 PCB, as a test for the LCD, the display works fine.

I am aware of the screwed-up EXP1 and EXP2 PCB silkscreen outlines on some PCBs so I have tracked the pins from the display to the PCB to ensure that they are all in the correct orientation. This is born out by the fact that they work at first.
My question is: how can it work one minute and not the next? And why does my old PCB work fine all the time?

I have tried uploading a sketch and the compiling and upload appear to work normally. I have the polite 'Thank You' at the end of the upload but still no characters on the LCD 2004.

Pardon my complete ignorance on this subject but I'm wondering if it is possible to 'de-flash' the USB chip which could affect the operation of the LCD?

My only other conclusion is that I have two dud PCBs in a row. A pretty unlikely answer, but I'm getting desperate for some progress with this problem.
As always, any suggestions gratefully received

Thanks,
Scintilla.

[geneb]

If the display works fine on your RAMPS board, then there's nothing wrong with the display.

g.

[Scintilla]

Hello geneb,
Thanks for replying to my post and, yes, it means the problem is not with the LCD itself.

I think there is something amiss with the way the Arduino IDE communicates with the RUMBA board(s) via the USB interface. I have no idea how this works but I understand the USB chip needs to be 'flashed' with some code so that it can communicate with the ATMEGA 2560 and the LCD display.

I'm wondering if I'm somehow crashing the USB code because I have had issues with the wacky EXP 1 and EXP 2 socket orientations on different boards. This might explain how my old RAMPS 1.4 still works with the LCD 2004 but at least two RUMBA PCBs and a TANGO V 1.0 have gone out to lunch.

I fail to see how it's possible to mis-orientate plugs and sockets without doing some mischief to the electronics. Some PCBs come without the black plastic shroud and some come with the shrouds the wrong way around. The attached picture shows two electronically identical boards with completely loopy markings.
I have traced individual pins back to the PCB to ensure which EXP is which so that mystery is solved. It's easy to refer to the circuit schematic to match, say, the 5V pwer and Ground pins to the appropriate socket.
Having done all this tracking I still have three dud PCBs and one good old RAMPS and a good LCD.

I think the next step is to try to teach myself how to re-flash the USB to restore the LCD operation...

If it sounds like I'm 'clutching at straws' it's only because I am

Thanks again for any comments,
Scintilla