Gottliebs system 3 combines the strobing of the switchmatrix and lampmatrix. Strobing these is done by the driverboard. Is the controlled illumination working? If not, checking the appropiate fuse is the next thing to do at the transformer assy. Reading the switches is done by the CPU board.

Hmmmm.....tricky......is +20V present at the driverboard?

The whole flippercoils circuit is solitairy...... Not driven by transistors at the driverboard. There is a sensorboard with optocouplers however which interfaces between flipperbuttons and switchmatrix. This board is located under the playfield. Are you using the flipperbuttons when navigating through the diagnostics menu? If you can, there is a part of the switchmatrix working. If not, you can try to disconnect it and see if there is a change.

Q17 is controlling a "left bottom" flasher. How can this be related by miswiring the left flippercoil?

I am something missing here. When miswiring the coil, the diodes at the coil will cause the flippercoil fuse to blow when pressing the flipperbutton. The diodes won't probably survive too. Nothing more. Or ?????