The game boots, plays, and scores. The problem is the drop targets won't reset and the target saucer related to the drop targets won't kick out the ball. They score points, so I'm guessing the MPU sees those units. They don't react to the solenoid test, but do reset and kick when I ground the transistor ground tab. I have an AllTek MPU and a completely rebuilt, and tested, original SDB in the game. These two solenoids are controlled by transistors 11 & 16 on the SDB. I have replaced every component in both of these circuits. The associated IC's have been replaced. The male pins have been re-flowed and most of the female connectors re-pinned. I have put two other circuit boards in the game and the problem remains. There is 43vdc at both coils and they are good. I am assuming the ground signal is the problem but I am not sure how to isolate the problem. I am about out of ideas, so I'm reaching out to the brain trust. Any, and all, suggestions will be greatly appreciated.

All the other coils on the play field fire, but I changed the fuse holder and fuse just in case.

Tested the transistors before I put them on. And you are correct, tab grounding was only mentioned to indicate that there was a clear path from the transistor to the coil. I have put in at least two other SDB's and gotten the same result. Very frustrating.

The game has a new AllTek ultimate mpu in it, on top of that I had another alltek mpu on hand which gave me the same results when I put it i the game. I replaced all of the female pins on the mpu and the sdb, and verified, with the schematic, that the connectors were pinned correctly.

The common power wire is yellow and I have 44.7 vdc at both coils, my problem is in getting ground to those coils when the contact is made. If I ground the tab on the associated transistor, the coils fire. I appreciate all the effort, keep 'em coming.

Earlier, I had bypassed all the game wiring to no avail. Found the problem though, a new U2 socket was bad. I'll start continuity testing them before mounting from now on. Thanks to all.