A "gentle tap" on the neckboard could point towards dirty contacts on the CRT neck pins, or dry joints on the neck PCB. Be VERY careful working on anything near the CRT, or boards. If you are not sure, call in a tech. If it is a dry joint, it is a 10 minute fix.
Have you read through the P2K Wiki ?
https://pinwiki.com/wiki/index.php?title=Pinball_2000_Repair
