Hi There. I have this weird device that is not fully working.
It is a keypad used to control several tools in a harvester. It uses CAN bus to communicate with the devices in the machine.
When it is powered on, it should flash all the buttons for a second, and then only the functions that are active, should remain lit. If you press a button, it should send a CAN msg and corresponding light behind the button should turn on/off.

The broken keypad still keeps its control abilities 100%, but you have to work blind, as the leds behind the keys don't light up at all. No powerup test flash, no working lights, nothing, but when you press a button, the specific tool is activated, so CAN connectivity seems ok.

Inside, it has 2 boards.
Board A (check pics) has connections to harvester. Only 12V, GND, CAN-H and CAN-L are used in a real harvester. It has several transistors, probably for functions that are directly driven by the board, probably connected to the spare plugs, never seen them in use.
It has a small connector to board B. Connector only has GND, VCC, CANH/L and 2 more unknown pins.

Board B has all the logic to drive the CAN signals and the LEDS. LEDS seem to be RGB, as they are driven by several pins, and I have seen them flashing in different colors. Each key has 2 leds. One helps you locate the function it does at night, other turns on/off whether the associated tools is activated or not. This is the faulty board, when I use this board on another Board A, it still fails.

IC's on this board a
1xTLE4473 GV53, this is a LDO dual output regulator, for 3.3v and 5v (5v seems to be inhibited and unused)
2x762T, these are power FET switches. I think one activates TE11 and other activates TE12.
1xA1051/3, this is the CAN line driver, to interface with microcontroller
2xTCL5943, these are 16 output LED drivers
1 microcontroller
1x93LC86, this is an EEPROM for the microcontroler

As everything but the lights seem to work fine, I believe the problem is in some current driver for the LEDs set, but I can't tell how it could be driven.

I have a complete working set and another broken set (only board B is actually failing, as tested exchanging boards)

Can you provide any help on how to diagnose what could be wrong?

I uploaded pics of both boards (you can ignore board A) on both sides, and one of front B with annotated IC's markings

Thanks in advance!
Link to photos: https://drive.google.com/drive/folde...Df?usp=sharing