Quoted from seb951:Hi There, i had just about the exact same problem. Single lamp test would light other lights in the matrix on multiple rows. What it was is I had a few of diodes solder backwards in three lamp locations. In my case, both R2D2 Dome Left and Right and the Jabba's right power scoop light. Soldered them the right way and everything worked. Go over all your diodes on the playfield for the lamp matrix. I didn't change any of the LEDs so the messages about that are just plain false --- as I have LEDs from just about all the manufactures including incandescent regular bulbs .
A worthy resurrection.
This is dead on. Having a hell of a time with a row in a Hook i just bought. It had no light board for the ramp inserts and made the inserts light with #47 sockets and connected them to the existing molex. I couldn't for the life of me figure out why I was having issues. Transistor tested fine but replaced, the capacitor was missing and installed, SCR replaced. Everything the problem wouldn't go away. Sure enough, pulled out the 500K light bulb and away went the glowing row of lights. (For the record: the diode was shorted at the light bulb)
Good call Seb