Picked up a Jurassic Park a while ago. When I got the machine from the former owner he stated that the left flipper was not working. After getting the machine home, found out that the former owner had replaced the left flipper coil, end of stroke switch and the flipper board with new replacement parts, but the flipper still did not work. Checked the flipper board and F3 Fuse was blown, which is the circuit for the left flipper, note right flippers work just fine. Replaced the fuse and it would just blow again once you tried using the flipper. Pulled the flipper board out and began testing.

The following items tested bad on the board for the left flipper:
F3 blown fuse
D6 1N4004 diode shorted
Q10 TIP36C Trans. shorted all terminals
Q9 TIP32C Trans. shorted all terminals
R20 47 ohm resistor tested 11ohms
SR2, not sure if bad, but tested as the same for the right flipper circuit.
All other items in the circuit, appeared to be OK, tested the same for the right flipper.

I then replaced all items above, except the SR2 trans. Rechecked all items tolerances and they all appeared to be the same as the right flipper circuit now. Reinstalled and tested.

Left flipper again did not work. Recheck the FB and F3 again was blown, I mean, really blown, was black a bit in the glass tube.

Pulled FB out again and all the same items above are again shorted or bad.

Could there be a short in the wiring? I am not sure as what is wrong. Wires do appear to be OK.

Last note: did talk to the previous owner and it appears that this same problem was happening with the older parts that were in the machine before he had replaced them. This leads me to think there is something else wrong other then the board or the flipper coil.

Is there anyone that could help me in the direction of what to check on next. Any help would be great.

Checked power coming into the board as follows:
Connector side CN2 pin 11 & 12 should be 50VDC, tested at 75.1VDC
Connector side CN1 pin 8 should be 5VDC, tested at 4.9VDC

Your thoughts

I guess this is why I am scratching my head to what the problem is as the first time I thought I had checked all the components that are around the area of the problem and/or the section associated to the left flipper. Again it appeared to be just the components close to the F3 fuse. Checking further in and they appeared good. I guess I just don't want to replace the same components again and have the same results again. I don't mind replacing the parts again, but would like to have an idea that the problem would be fixed or I found another problem that I repaired along with the same components.

Would you think the problem is else where other than the FB that would be causing the shorts? Or is this where the problem is and I am just not replacing all that's wrong?

I have just checked every components that is associated with the left flipper circuit and the only ones that tested bad are the original ones that I first replaced. Disconnected the wires leading up to the flipper coil and checked for shorts to ground and found none.

Please is there anyone that can help me shed some light on what is wrong or what to check next. I feel replacing the 5 bad parts again will result in the same failure. Any ideas.

Thank you Hawk007 for your suggestions, I will give it a try and look today!

Update, I removed the same items above on the FB. Checked all traces and everything appeared good. Replaced the components again on the board. Also looked again on the machine itself for possible other problems. Replaced the flipper coil with a new one just in case it was the problem. Reinstalled the board and turned on the machine. Started a game and the flipper worked!

Conclusion: I am not sure as to what the real problem was, but am happy that its finely working!