I've got a Williams Pharaoh that I recently shopped out, rebuilt the power supply, fixed some minor battery corrosion and replaced the 40 pin connectors on the MPU and driver boards. Everything is working great except I'm having issues with 2 columns of lamps (columns 3 and 4). They blink on and off correctly in test mode but during attract mode they are strobing. It's really noticeable with the PHARAOH letters on the upper playfield. The lights don't blink on and off correctly to spell PHARAOH in attract mode and they are all strobing. I'm using all incandescent bulbs. I've checked the diodes on all the insert lamps and they all look good.

I thought it might be an issue on the driver board so I grabbed the driver board out of my Blackout and it does the same thing so the driver board should be good.

Any ideas on what would cause this?

I checked all the diodes and wires on the affected lamps and they are fine. Any other ideas?

I just figured out the problem and it looks like it's been like this since it shipped from the factory! The problem was the 7 position lamp board for PHARAOH on the upper playfield had all 7 lamp sockets soldered together with the bare wire. This was causing the Yellow-Orange and the Yellow-Black wires to be connected as there is one of each soldered on the two ends of the lamp board. I clipped the bare wire between the R and the A lamp sockets and now it's working perfectly.