This may be Data East related, not just BTTF specific.

I purchased a BTTF with some issues. I played fine, but the bottom pop bumper coil had melted, taking the driver and pre-driver transistors with it. I replaced the coil and the transistors, and also repinned J5 on the PPB board that had been done badly by the previous owner.

Now on startup, the top left, top right and left slings are locked on. All other driver transistors have been checked I'm sure there's a simple explanation but I can't seem to find it. I've linked another post about other issues with this game, maybe they're related.

https://pinside.com/pinball/forum/topic/bttf-issues

Did some reading and found this anomaly with respect to DE Revision 3 games:

http://techniek.flipperwinkel.nl/desega/index2.htm#trans

Based on this, I did some investigating in the basement and found one diode (D2, 1N5234) and its associated capacitor (C42, 0.1uF) are a dead short; both are on CN18 which is not used in BTTF

I also checked some resistors on CN19 which is used on BTTF and found the following:
- one 560 ohm resistor (R21) only reads 280 ohms
- all 6 2.7K resistors (R20, R22, R24, R26, R28, R30) read low, between 1.28K and 1.91K

So I'll be replacing D2 and C42, but what about the resistors? Are their low resistances of concern? Should I be replacing those as well?

Upon further investigation when I took the MPU board out for repair there was a sh!tload of battery corrosion that wasn't clearly visible until closer inspection, far too much to repair. So I broke down and got a new Rottendog MPU ($450 CAD before shipping, yikes!) and she's back up and running again.