Did you replace the small predriver transistor? I think (76 78) I had same problem, had to replace q77,79 predriver and u50, while the Tip 122s are what it calls for, most upgrade to the better Tip 102s. Do you have a schematic?

This is for the upper coil. Did you check ZR7? Its for the lower coil. Also did you check the switch that activates the lower coil, It may be stuck closed. You should disconnect power to the lower coil while you are trouble shooting or you will burn up Q-79 again.

99.9% of the time they look just like the day they were installed in 1987 even when bad. They explode when 70 volts are applied in stead of 5 volts.

There is a manual you can download for free.
http://mirror2.ipdb.org/files/804/Williams_1987_F_14_Tomcat_Full_Manual.pdf

Page 48.

There are snubber relays below the p/f, but the lower diverter is controlled by special solenoid #6 directly.

That is where I was going to send you looking, but since you found it already you should know that it needs a 2.5 amp sb fuse.

You should know this is a problem now, and not replace it.

All this is going to do is melt coils and burn more components on the CPU board.

Sheesh don't use a bigger fuse, thats just asking for trouble.

The first thing I would do is a resistance check from ground to the metal tab of Q-69, Q-71 and Q-75. If they are still original style TIP 122 you should have .5 meg or greater. If they are TIP102 you should see .9 meg and higher. If resistance is low then replace the driver and predriver and coil diode as a set. When the diode is off the coil you should check the coil resistance (23-800 coil is 4.2 ohms). After that is done its time to power up the game into attract mode. You need to check U-45 pins 5, 9 and 12 which should be high at this time, then activate each switch input (skirt for pop bumper) and the corresponding pin on U-45 will go low (pin 9). Once all 3 switch inputs have been checked and passed testing then check pins 6,8 and 11 of U-45 should be high, then start a game and all 3 pins should go low. If this checks out then recheck pins 5,9 and 12 now that a game is started, they should still be high. Now check pins 4, 10 and 13 they should be low when a game is started but go high when you activate a switch input. Start with this and let me know what turns up.

No problem, glad every thing is fixed. Now play ball!

pookycade GRUMPY Hey there. I'm having a similar problem with my F-14 in that my coils on the diverter solenoid would instantly fire when I turned on the machine and if I didn't turn it off, they would literally burn up. I replaced the coils and the Tip122 transistors on both Q77/Q78 (or whichever were the ones tied to the lower/upper diverter coils). Now they don't fire at all during gameplay or solenoid test.

Just trying to track down what to try next since my initial repair seems to have done nothing except prevent the coils from firing at all.

I should mention that everything else is working as it should. Flippers, coils, etc. It's just these two darn diverter coils which really makes the game boring.

Instant firing on power up is usually a shorted Zener diode. Check the corresponding zener diode prior to doing any more testing, since that was the original issue.

Edit: If the Zener is good, you can try and manually short the TIP122 tab to ground quickly to actuate the diverter coil to rule out the TIP122/power side of things. If it does, then it is just the switching side of things, which would likely be the 7402 TTL.

Also, those Zener diodes in that section are your line of defense for accidental higher voltage dumping onto the logic side of the board. Those are supposed to dump offending higher voltages to ground. So they're pretty important in protecting your MPU from a massive cascade failure. The fear of those zeners being in an open state is legit.

When you replace a driver (TIP122) you should always replace the corresponding predriver (2n4401) also. To do further testing you should buy a logic probe. Its also a good idea to install a under play field fuse for each of the diverter coils with a 1.5 amp sb fuse.

About the fuses on the diverters, if you added them on yours would you mind sharing some pics, I have had diverter problems on mine and while I know how to fix it, I never figured out why it happened, and have read a bunch of other people that have had the exact same problem.

I've always mounted screw-on type fuse holders just below each diverter/special solenoid controlled part. I'll usually cut the power wire about 6-8"from the coil. There is almost always plenty of room to install them without worrying about the tabs touching anything.

Another option would be to install Andrew's special solenoid saver PCB that goes in the backbox. http://nvram.weebly.com/repair--conversion-kits.html

Here you go. Not the best pic because I have black lighting in my game room. Im with thedefog in that I normally use fuse holders that screw to the pf but F 14 is real busy so I used this type. These crimp right to the control wire in less than a minute.

20171117_104143 (resized).jpg

Cool thanks everyone. I will replace the corresponding predriver and see what happens. I think I can also handle the 1.5SB fuse holders. Thanks again.

Wanted to thank everyone for the assistance. It was an issue on the MPU and it made it's way through several transistors. All repaired and working now!

Playball!