Display not working

Hello everyone,
On initial power-up my display did not function.
The printer head connector was unplugged as per the instructions.
the contrast pot, reset and other buttons did not help.
All end stops lit up (as expected from robv’s subject “Are the LED’s supposed to be on all the time?”).
On the control board; LD4 (ext1 heater), LD5 (ext2 heater) and LD6 (bed heater) are lit up red and LD14 (not on the schematics?) is green. Maybe the LD4, 5 and 6 indicators are expected as there are no temperature sensor inputs on any of them.
Driver boards and main board electrical connections look OK, cable to the display was corretly placed and the display to SD board connection looks OK.
Checking the power to the display from the board at CN1 shows that the 12V pin is at 14V and the 5V pin at 0.8V.
Any suggestions?

Are you able to make an USB connection with the printer?

(Just to make sure the mainboard is working.)

There was someone else that had a problem similar to what you are seeing.
His issue was he had the fan plugged into the reset plug.
Try unplugging all of the connectors (except the LCD) apply power to the printers and look at the heater LEDs and see if the display is working.
If the heater LEDs are on do not plug the print head in.

I tried connecting to the board via USB with no success. The arduino software did not recognize it, no sound from the PC recognizing a device was plugged in. The PC did not try and load any drivers or anything like that. I have not used this type of device before, so I have no reference to go by, but as far as I could tell I was not connecting with the board.
Also pulled out all connectors but the display (motor drivers left in place) - no change in the display (still dark) LEDs on the board the same as before.
Any other suggesations?

I would also remove the stepperdrives from the board,
I had one misaligned and the board didn’t come up at all… after resinserting it ok it all worked again…

Looks like success!
Unplugged everything from the board including driver boards - computer connected to the board, everything looked good with main power connected as well.
Added the display - lit up and worked on USB power, everything looked good with main power connected
Added the driver boards, checking for connectivity after each one inserted - all good
Added all other connectors everything looks good. No red LEDs except the axis limit switches
I think it was something to do with the driver boards, maybe one wasn’t seated correctly - thanks mhensen
I have not updated the firmware on the board yet, but for now success.
Thanks to all of you for your suggestions