Could you provide images of the circuit boards in the head?

I'm just curious if there is "battery damage" https://pinwiki.com/wiki/index.php?title=Bally/Stern#The_Single_Largest_Culprit_in_MPU_death

also if you have original or replacement boards

There are some troubleshooting steps to isolate where that short may be coming from if not from battery corrosion ( I don't have them at the top of MY head but other Pinside members do )

The boards visually look good , battery had been removed from MPU with "NVRAM" installed

New capacitors on SDB and some voltage regulator upgrade seems to have been done

In the pic of the playfield I noticed 2 balls locked in the "ball-walker" (or ladder) area. Upon start up that is one of the first solenoids to fire (along with the coin reject solenoid on the coin door)

With power off,First visually inspect those 2 to see if they are burned , you should be able to manually actuate the "ball walker" solenoid to release the balls

If you have a multi-meter it's be best to test for a resistance on those coils. you can manually actuate all the others as well.

nice catch by oldschoolbob

The rectifier board image does show fuse "F4" being blown , the confusion is the "e3 test point"

On the SDB it's tough to see if the components surrounding "q13" are ok , also on the schematics it's tough to distinguish the difference between the associated "Ball launcher" and the "ball kicker"

There are times if either the coil or a board component fails that drives the coil it takes them both out.

It's great to have both slochar & Quench on this thread & their diagnostics by removing connectors will help quickly resolve the culprit.

Stern F2k - q13 (resized).jpg

Stern F2k ball launcher - kicker (resized).jpg