My Diner playfield had an issue that is very common with this game – raised inserts in the middle of the playfield. Both the character inserts as well as the DINER inserts had the problem. During play, the inserts would cause the ball to jump around at high speed, and divert the ball along an unnatural path at low speed.
I first removed the insert lamps PCB and moved the flashers aside to gain access to the inserts, then heated them one at a time using my heat gun.
Then, from the topside, I used some small pieces of poplar wood to press the inserts down by hand. I first used a rubber mallet, but evidently just pressing by hand was enough to push them down to level.
In the photo above (click for a larger image), I am halfway through the character inserts. I have leveled the Haji and Babs inserts, but Boris and Pepe clearly are raised above the level of the playfield. After repeating the process for all these and the DINER letters, the game plays so much better now! The ball rolls smoothly over the playfield with no jumps, bumps, or deviations. Awesome! 🙂