HP LaserJet M9040 dark Panel, no image

[rvalente]

Hello Mates,

I've a M9040 at the office, few years ago the control panel died but, we kept using through ethernet, no one used the scanner anyway. Suddenly it seems the network config was off, could not find its IP any more so, time to fix the panel (yeah, great...  )

The display is blank in all contrast range, no image during the turn-on/warm-up process. The touch and the keyboard are responsive, If I press copy the scanner and printer works normally.

I was playing with the board and resetted the LCDs flat cables while the board, once the image came back perfect for a few seconds, the printer finalizing the boot/warm-up and it went dark again. I'm suspecting of a poor power supply for the contrast. The photos does not make justice but its possible to see something very dark in the upper left corner (ready/warming, but in portuguese).

The control board is made by Optrex japan, is a XILINX FPGA + Epson LCD controller (seems to handles the touch and the display).

The comms with the formatter board (name given for the printer motherboard) seems to be clock + data in + data out, the service manual gives little to no information on schematics, attached the few useful shots. The 24V and 3V3 signals are fine.

Anyone has any idea or tip for where to start?