The fact that it resets when you power it up and the issue coming and going with power cycling are pretty good clues that it probably isn't a playfield diode at fault. Check +5VDC logic supply at MPU IJ17 Pins 4,5,6 = +5.03 VDC @8.1 mV AC ripple. You might have a failed filter capacitor or bad regulator, or even a bad cable crimp. Increased current draw when activating your flippers is likely causing the supply to dip enough to trip a reset.

Just so you know, sometimes you CAN tell if a diode is bad by looking at it (i.e. it will be crumbling, or cracked) but visual inspection of a component doesn't tell you much if anything about if it's good or not.

I agree with wayout440 that it's more likely to be power supply and connector related though. 32 years for a filter cap is a long time.

If your dmm lead probes are not needle sharp, you can grab the positive voltage from one of the first components the logic voltage feeds into, such as L1. You want to keep the harness plugs installed, as that provides a load and an accurate measurement under running conditions.

All you need to do to measure AC ripple is leave the dmm probes in the same location and switch your meter to read AC voltage.

like others have said it sounds like a cap not doing its job until its warmed up. double flipping pulls the 5v rail down causing a reset when the cap probably would keep it high for the brief surge.

I always replace all power supply caps on a game like this vintage . Reflow ps header pins. Check large ac input connector for burned pins as well.

https://pinside.com/pinball/market/shops/1013-kahrus-circuits/00092-wpc-power-fix-daughterboard
Get one of these, works great.

Magic bullet board doesnt work with System11 games.

OP actually has to properly diagnose and fix this one.

Unfortunately F14 is not WPC. But that WPC daughterboard won't help you if J101, J114, J210, Z-connector or C31 are bad.

Yup. Might not even be the power supply itself...could simply be a worn out oxidized connector pin. Troubleshooting is more cost effective than throwing in parts randomly anyway. However, like when I actually determined my power supply to be failed on some system 11 games I purchased modern replacement power supplies for long term reliability - which generally had newer, cooler running components and nice features like LED status indicators. I did this with several system 11 games like Taxi and F14 Tomcat. Then the removed units I sold online for cheap spare parts. On average you might buy a new system 11 aftermarket supply for around $100, get about $20 back from selling the old one....but won't help you much if the original problem later turns out to not be caused by the problem power supply in the first place.

Not really. Band aid for an underlying issue that will occur later on down the road. Good to have in a pinch where you HAVE to have something up and running for a party or tournament, but not a viable long term fix IMO. Fix the board properly.

And as others have pointed out, not appropriate for F-14.

4.98V isn't bad for the DC voltage. What was the AC ripple voltage?...that will provide info as to if the filter caps are good. You might also try the flipping again while measuring to see if there is any change. If you find one flipper causes it but not the other, I would be suspicious of a failed flyback diode on that particular flipper circuit.

Here is also a link to some discussion about the U10 failure message:
https://pinside.com/pinball/forum/topic/u10-pia-failure-where-to-find-and-replacement-repair-advice

That is correct.

This should be over 12 volts. This should be checked at the power supply to determine whether you have a bad connector or you need to rebuild the power supply.