Running into an issue with the Bally Spectrum I’m restoring. All new Alltek boards as well as new power supply board. Only original board left is the S&T. Turn on game, all board LEDs and test points (both PS board and Alltek boards) show proper voltages. All fuses checked. Displays work, coils fire, one can start a game and switches register. However No GI, Insert, or backbox lighting.

A bit baffled on this one...thoughts??

Alright, thanks for the input everyone. After some troubleshooting I was able to resolve the problem: intermittent bridge rectifiers on the power supply module board. This is a new board from PBL, and would sometimes read correctly at the test points, other times they would not. Once BR1 and BR2 were removed and replaced with new bridges the board and lights worked fine. Interesting part is once removed from the board the "defective" bridges tested fine! Best I can figure wherever PBL had these manufactured the automated soldering process was not able to get the solder to wick up from the bottom of the board to the top as it's a 2 sided PCB.

For reference, as BigAl56 mentioned, there are 4 aux lamp driver boards in this pin on top of the 2 main lamp driver boards. 1 of those aux driver (with triac mounted) is used exclusively for the 4 #921 bulbs in the top of the backboard. The 3 remaining AUX driver boards are paired with 3 TRIACs. 2 of those aux boards are mounted under the playfield, 1 is mounted on the back of the backboard. The 3 TRIACS are mounted in the cabinet to the power supply metal panel. Each Aux driver board/TRIAC pair powers a distinctly different GI set (Backbox, Left side of playfield, right side of playfield). Each pair also has a set of specific bulbs that it triggers off of, once again backbox, left side of playfield, right side of playfield. That is how the GI is controlled off/on during gameplay.