Working on a Firepower pop. Lower left to be specific.

Background:

Discovered that the lower left pop wasn't activating. Didn't do any troubleshooting because when I opened up the playfield, and took the bumper apart, it was apparent that the coil was fried, and the sleeve was melted. So off to Marco for replacements. (Coil, plunger, yoke, etc, and new parts for playfield.) Following the guide, I was able to successfully rebuild it, or so I thought.

Also, this game has a new Kohout Driver Board connected to the original MPU.

Issue and symptoms:

I have 32.X volts across both lugs on the new coil. It is wired correctly, the red wire is consistent across all the other pops and oriented correctly to the diode. (double and triple checked....)

Still not popping, however I do have connectivity from the switch back to the driver board. So I know the switch is making contact.

The Orange Red wire (Pin 3) is showing 4.89 V at the driver board. Other pops show 4.9 to 5.0) When activated, nothing happens and the voltage goes to 20.X, while other pops go to 60.X. (I know not to hold it down for a long time, )

The switch looks original. I know there is a capacitor and a Resistor in line from the two blades that connect when contact it made on the skirt.

The scoring is working correctly.

So now I am at a loss. What other further testing can I do? There is a Green Yellow that traverses the underside of the playfield. Would that voltage help?

Also I am NOT opposed to rebuilding the switch. PITA location wise, but I am getting better each and every time I work on the machine. If the recommendation is to rebuild, what are resistor, capacitor, and diode components as I can't seem to find a BOM for the switches anywhere......

Thanks in advance for any help.

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OK just ran the test, and nothing registers. All the other pops register, this one does not.

Switch replacement time? Or are there other things I can test for.....

OK, the switch is making contact. I get a continuity beep when I press the two leaves/contact together. Is it possible the contacts are badly corroded and not allowing enough juice to get through to active the solenoid? I have some blades and contacts in the tool box. Not sure if I would use low voltage (gold) or high voltage contacts.

Scoring switch is working and registering scores.

I can make electrical contact both by touching the skirt, and by pressing them together.

Amazing what you figure out after some sleep. This has nothing to do with the switch. The coil isn't firing during the coil test. (I knew that last night, but it didn't register.....) Something is amiss somewhere else. I will open a thread in Early Solid State. Thanks Vid for the guide, I am sure once I figure it out all will be well.....

Run a jumper wire from the side rails (ground) to the NON BANDED side of the coil diode. Did it fire?

-Yes it fired.

If it did, now ground the TIP transistor tab of that pop's driver transistor. Did it fire?

-Yes it fired.

If not, then you have a connection problem between the driver board and the pop coil.
If it did, now look at that driver transistor and the little pre driver transistor next to it.
Testing TIP102 style of Transistors :
Meter in DIODE mode.
Black lead on center tab of transistor (there is a hole in the center tab - it's right on top of the transistor).
Red lead tests each outside leg.
Readings should be between .4 and .6

-May be a variation in the way that the Kohout board is wired, but when I did this, the meter went to "-" in Diode mode, for each leg, no value shown.

-When I tried the same test on another TIP transistor for the other pop bumpers, it did the same thing, with one exception. When I touched the left leg, it fired the solenoid. It did NOT fire on the transistor in question. (Hmmnm)

If you reverse the set up and put the red lead on the center tab, the outer legs should read 0.
Test your work by checking other transistors of the same type on the board.

-Got 0 for each leg, and again the same result as above. Touching the left leg fired the other solenoids, but not the one in question.

Q18 (Transistor in question)

Black lead on center tab
Red right - .456
Red left - .456

Red lead on center tab
Black right - No Reading
Black left - No Reading

Q19 & others (Transistors known working)

Black lead on center tab
Red right - .456
Red left - No reading

Red lead on center tab
Black right - No Reading
Black left - No Reading

So my results are two posts above. Based on the results, the transistor is NOT behaving vs. the rest of the others?

So what say the smart guys? Replace the transistor? This is pretty easy to do, the Kohout boards are very serviceable.

Thanks guys! I just want this pop to work so the game at least plays correct.

Completely understand. I have the BOM for the board and the part is IRL520n. I have a query into Ed @ Great Plains to see if I can get a suitable replacement.

If this was a pure Williams board, and the issue was a locked on coil, what would you replace? Just the transistor or other components?

Update:

I spoke to Ed @ Great Plains, and he recommended an IRL 530n as a suitable replacement. I also had a chance to converse with the Kohout brothers down in Texas, and they responded very quickly. They indicated that likely the mosfet was likely toasted, and that they could either send me a new one, or I could opt to send the board in and have them repair it for $20 bucks including return shipping. I thought this a very fair offer.

I am going to be brave, and attempt the repair myself, using the IRL530n GPE will send me..... Their boards are clean, and easy to work on. If I fail, I will send it back. I won't fail!!!!!

So by this weekend I should be able to report back if I can get the pop bumper running again..... Fingers Crossed!

Well, an update:

Indeed, I did blow up the mosfet on my new Kohout board. I replaced it with an IRL540. I bought an IRL530, but Ed sent me the more robust ones, and promised me they would work. I de-soldered the burnt out part, and put the IRL540 in.

The other problem I was having was that the skirt was getting hung up on the spoon, on certain angles. So I loosened the screws to the bracket that holds the switches, repositioned it, and tested it. No more hang ups.

I put it all together, crossed my fingers.

I now have a 100% working Firepower.

I want to thank Vid and all other posters that helped me through this. I bought this game for my son one year ago for Christmas. And now one year later, almost to the day, it works.

I no longer fear the pop bumper. However I think there is a better way to do them. I am going to ask in a new reply. The lamp holder is a huge PITA. I have an idea.....