Also from Clay's guide, general common issues with System 11 lamps:
Most Common Problems with Lamps.
Bad bulb. Any light bulb can burn out. Often you can visually see the bulb is burnt, but sometimes you can't. Test the bulb with your DMM, set to continuity. Put your test leads on the bulb. No continuity, and the bulb is bad.
Wire broken away from the socket. This happens quite often and requires re-soldering the wire back to the socket lug.
Diode broken away from the socket. If the lamp diode becomes disconnected from its socket, the lamp will not light.
Corroded or Bad Socket. Games imported back into the US from other countries exhibit this problem more often. Re-seating the bulb in its socket often fixes this problem. On 555 plug-in sockets, bend the contact tabs slightly for better contact.
Blown Fuse. If several GI lights don't work, check the fuse associated with them. If all the CPU controlled lamps don't work, check the fuse by the BIG 30,000 mfd capacitor and bridge bolted to the back of the backbox.
Burned Connector on the power supply or interconnect board. This happens most often with GI (general illumination) lamps. See Burnt GI Connectors for more info.
Lamp matrix power resistors. On the CPU board, lower right corner, there are eight .4 ohm, 3 watt wire wound sand resistors (R113, R116, R119, R122, R125, R128, R131, R134). Sometimes these resistors get hot and de-solder themselves from the CPU board and fall off (or the solder joints need re-soldered).
Bad Column Transistor. The TIP42 transistors that control the lamp matrix columns often fail. If this is the case, all the lamps in a particular column will be brightly locked on.
Two Lamps act as One. If a lamp diode has a shorted on, this can cause two different lamps to act as one.