I am closing this post as problem solved. Let me recap the issue so folks do not have to read this long thread, my attempts to fix the problem, and the workaround/solution.
1) q relay was disengaging randomly during games. Sometimes I could play with no problems, other times it would disengage several times during a game. This would cause the upper playfield to go dead for a few seconds and then reactivate when the q relay re-engaged.
2) checked all switches, made necessary adjustments on switches that would activate the q relay. Checked switch to lower playfield as well. Also checked connections at the switch and the diode.
3) I next checked to make sure all ground mods had been properly done. Everything checked out okay.
4) I next looked at the driver board connections and harnesses. I discovered that by pressing on the A3J2 connector with my thumb I could cause the q relay to disengage by slightly flexing the driver board. I rewired A3J2 twice and the adjacent double sided connector A3J3. I also checked all wiring at each connection against the schematics to make sure everything was wired correctly - very tedious took most of an afternoon. Everything was wired correctly. I also added a thin layer of solder to the edge connectors to build them up a little. None of these efforts solved the problem.
5) I went back to the schematics and looked for pathways on the driver board that affected the q relay. I started bypassing parts of the driver board by wiring directly from the top of an edge connection to its associated transistor. This was trial and error, but finally found the path that was causing the problem. It was A3J2 connecting up to A3J3 transistor Q2. See attached picture. Q2 transistor controls the tilt relay but then connects to the q relay controlled by Q1. So bottom line there is a connection problem on the board - maybe a hairline crack or poor solder track.
Thanks to everyone's help with this problem. Moral of the story, persistence, patience, and systematically going through the steps to fix the problem payoff. It also helps to have knowledgeable people from pinside guide you along the way.
P.S. I have corresponded with Ace - David Hunphrey - at NiWumpf several times along the way. It is a Nisumpf driver board. I cannot say enough positive things about his help. He has offered to fix the board at no cost, and at some point I will send it to him. Right now I am going to enjoy playing a fully functional Black Hole!
Thanks again for everyone's help.