I had an interesting lamp board repair recently. Lamp board would sporadically lose all lamps that were driven by u4. It was all or nothing, and the lamps would come and go with pressing/flexing on u4 (u4 was already socketed). Poking around on the bench revealed that r71 was cracked, which sends the PD3 signal to u4, and flexing the board would temporarily connect r71 back together.