Since all the LEDs are out, I would check is the + and - 15VDC power supply that powers the LEDs. Look for + and - 15VDC at the LED (R68, R70, R77, R79). There is a jumper J19 that you should reseat to ensure that there is a good contact and power is getting to the low voltage power supply. Then trace forward through the power supply to the LEDs.
Since all the LEDs are out, they are probably ok but they need to be checked. This can be done with a small battery and a limiting resistor. The LED will work or it won't.
The next step would be to examine the circuit that drives the LEDs. This gets more complicated.