Lamp 1 is exhausted.

Replace lamp module 1. See service manual chapter ."Lamp and Lamp Module".

Malfunction of the Lamp Ballast on the Lamp 1 chain.

Replace the Lamp Ballast. See procedure "Replace a Lamp Driver Board".

The lamp power cable is disconnected from the Lamp Ballast.

Check that the lamp power cable (reference 1 of image) is properly connected.

Malfunction on the ULCB module.

Replace ULCB module. See procedure "Replace the ULCB".