(Topic ID: 238390)

Firepower credit knocker problems

By mdhawkeye

3 years ago

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  • 17 posts
  • 5 Pinsiders participating
  • Latest reply 3 years ago by Schwaggs
  • Topic is favorited by 1 Pinsider


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#1 3 years ago

Refurbing a Firepower I bought a few weeks back. It's my first pinball, but I've done several other similar projects (jukebox, helped my son on a Blackout, etc) so am somewhat familiar with the workings. The credit knocker solenoid was toast...completely fried, dark brown and the knocker stuck in the sleeve. I'm assuming in a past life the sleeve got dirty, the knocker stuck and burnt out the coil. Replaced the solenoid and still nothing. When I pulled the driver board, I noticed the trace for the solenoid (#14-> pin 4 on SJ9) was totally burnt out of board...YIKES!!!! I replaced EVERYTHING in the path of that circuit...the resistors R68, R69 and R70, and the transistors Q40 and Q41. I used a tiny jumper wire to go from the emitter of Q41 to pin 4 to replace the trace. So far I've blown 3 TIP122 transistors. I figured the first was sloppy soldering on my part, the second I pulled because it was getting REALLY hot during the solenoid test, and the third sparked and cracked in half during power up :-O I tested voltage as best I can with a digital multimeter coming out of the resistors and the Q40 BEFORE Q41 and all seems to be in spec as best as I can tell (hard with DMM in the back box...suggestions welcome). Voltage off of pin 4 all over the map again because of my tools but off the emitter of Q41 when I can reach it seems correct, between 32-35V. I know the ICs in the path are doing the correct thing (used a logic probe to see that they were pulsing properly). I've looked at most wiring coming from board to molex, and molex to knocker and dont see anything obvious. I'm kinda lost now, and would appreciate the expertise of those who have been here before.


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#4 3 years ago
Quoted from Schwaggs:

When these transistors are burning, is the knocker firing?

Nope, it never engages at all

Quoted from Schwaggs:

Power up the board with the driver board connector that runs to the coils removed and see if the transistor still burns or over heats. If it does, you have a problem with the board.

One of the attempts I made yesterday, I did just this, and No, it did NOT get hot

I plan on looking at this again this afternoon. Will post the results. Thanks for your help!

#5 3 years ago

FRIED ANOTHER ONE ! hope there wasn't collateral damage to neighboring bits. This one came complete with smoke!

Schwaggs - Tested with the plug OFF the board. Transistor did NOT get hot, maybe warm but not like yesterday. I had it firing on the self test for quite a while. I don't think it got any hotter than the one next to it when I was testing it as well. Voltage at the knocker coil with the plug removed was ~34VDC.

When I powered up, I did NOT hear the coil energize or see the plunger get pulled up. I DID see smoke almost immediately coming off board. I pulled the board again to take a look. I don't see any apparent damage, but will replace the things in that circuit again.

I'm all out of spare TIP122, so will have to wait for my order from Mouser to arrive to try again. Any pointers appreciated.


#7 3 years ago
Quoted from Schwaggs:

Did you confirm the power wire is soldered on the correct side of the knocker coil (banded side of the diode)?

Yep...the wire coming from the connector (pin 4, brown/blue) is connected to the banded side of coil

Already ordered TIP122s Next time!

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#11 3 years ago

Thanks for the help...finally got back to this (life gets in the way of the important things... )... Swapped the wires, plug the board back, and KABOOM! Blew it again, but really bad this time. I had unfortunately closed the backbox so i could lift the table to see if the solenoid got energized....Thus I missed the explosion and the small fire that ensued! Obviously something more going on than just my stupidity in wiring the power backwards.

The little incident took out quite a few other nearby components. I replaced a bunch of resistors and a few transistors in the vicinity. and verified that everything back to where I started except that now I have aboard with quite the scorch mark. I probably need to dremel it out and fill with epoxy.

Before I do anything else though, I need to figure out root cause. I can only think that something in the wiring from the board to the solenoid got screwed up when the original solenoid went bad. I'm going to have break open that bit of harness and inspect more carefully.

Other options I can think of: 1) Do nothing, live without credit knocker (that doesn't fit my anal retentive personality) 2) repair board 3) send board OUT for repair and diagnosis 4) Is it possible to re-use one of the UNUSED solenoid circuits on this board that firepower ignores (i think 2,3,4 maybe). That would mean nasty jumper wires but I have one of those anyway.

All suggestions welcome. Thanks again for the assist.

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2 weeks later
#13 3 years ago

@schwaggs - Finally getting back to this - replaced all the bits that got burnt from my stupidity, dremelled out board, filled with 2 part epoxy, new jumper wire, new diode on the coil and.... now the coil stays energized when powered on! Progress!!! Hooked up logic probe and see IC5, pin 15 pulsing hi/lo like it should. I see IC4 (7408) pin 12 pulsing (other end of IC5-15), pin 11 (out)...nothing, 13 pinned hi. Do I interpret this properly meaning this IC is toast? or could it be socket or traces or schmutz between legs?


#16 3 years ago

Schwaggs - swapped in a new IC4 today and EVERYTHING WORKS!!!!! One rollover target to fix and I'm in business! Thanks for all the assistance. It is greatly appreciated. You pinball guys are much like the jukebox guys (my other toy habit)...always willing to share your expert knowledge so us rookies can learn so we can help others later on...great community!


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