(Topic ID: 214125)

WPC knocker firing repeatedly


By arolden

1 year ago



Topic Stats

  • 15 posts
  • 9 Pinsiders participating
  • Latest reply 1 year ago by herg
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#1 1 year ago

Hi everyone.

Trying to help troubleshoot a friend's FT. Any help is appreciated.

Basically, when the game is turned on and the MPU boots, the game will go into attract mode but the knocker will fire constantly. It keeps going off repeatedly until you turn the game off or you start a game. For now it is unplugged.

I have tested the transistors at Q68 (TIP 36) and Q67 (TIP 102) and even the 2N5401 predriver transistor. All test OK. The diodes and resistors associated with these transistors are also OK. Coil resistance is 4.2 ohms which is in spec for the AE-23-800.

Where should I go from here? I considered this may be a fault with the driving 74LS374 IC, but I have never seen these fail in a way that they constantly activate the associated component. Rather, when they fail the components seem to stop working instead.

Appreciate any troubleshooting advice.

#2 1 year ago

I would check and remove knocker coil and see if it is rubbing on the metal bracket and grounding out. Secondly, reseat ribbon from cpu to driver.
Beyond that it sounds like a weird issue.

#3 1 year ago
Quoted from arolden:

Hi everyone.
Trying to help troubleshoot a friend's FT. Any help is appreciated.
Basically, when the game is turned on and the MPU boots, the game will go into attract mode but the knocker will fire constantly. It keeps going off repeatedly until you turn the game off or you start a game. For now it is unplugged.
I have tested the transistors at Q68 (TIP 36) and Q67 (TIP 102) and even the 2N5401 predriver transistor. All test OK. The diodes and resistors associated with these transistors are also OK. Coil resistance is 4.2 ohms which is in spec for the AE-23-800.
Where should I go from here? I considered this may be a fault with the driving 74LS374 IC, but I have never seen these fail in a way that they constantly activate the associated component. Rather, when they fail the components seem to stop working instead.
Appreciate any troubleshooting advice.

Hi there,Did you test the knocker coil with a mutimeter to see if that coil has shorted?

#4 1 year ago
Quoted from pinballplusMN:

I would check and remove knocker coil and see if it is rubbing on the metal bracket and grounding out. Secondly, reseat ribbon from cpu to driver.
Beyond that it sounds like a weird issue.

Sure does sound weird,Lol!! Maybe your a pin wizard and the game is giving free plays!!

#5 1 year ago
Quoted from pinballplusMN:

I would check and remove knocker coil and see if it is rubbing on the metal bracket and grounding out. Secondly, reseat ribbon from cpu to driver.
Beyond that it sounds like a weird issue.

Ribbon cable from MPU to driver was reseated but no change in behaviour.

If the coil was grounding against the bracket, wouldn't it be constantly engaged instead of firing over and over?

Quoted from pinmike:

Hi there,Did you test the knocker coil with a mutimeter to see if that coil has shorted?

Yes that's how I measured its resistance. Is there a different method to test for a short?

#6 1 year ago
Quoted from arolden:

Ribbon cable from MPU to driver was reseated but no change in behaviour.
If the coil was grounding against the bracket, wouldn't it be constantly engaged instead of firing over and over?

Yes that's how I measured its resistance. Is there a different method to test for a short?

Power off,Meter set to ohms,place one probe on outer right tab of the coil,one probe on outer left tab of the coil.
meter should read 2 ohms or higher

#7 1 year ago

Will it do it in audit/diag mode? Is it random or does it go off with some regularity?

I'd go into test and cycle through, I wonder if it's going off at the same time something else should be.

#8 1 year ago
Quoted from pinmike:

Power off,Meter set to ohms,place one probe on outer right tab of the coil,one probe on outer left tab of the coil.
meter should read 2 ohms or higher

Yes it was 4.2 ohms which is correct for that coil.

Quoted from Slim64:

Will it do it in audit/diag mode? Is it random or does it go off with some regularity?
I'd go into test and cycle through, I wonder if it's going off at the same time something else should be.

I didn't try it in test mode - will do that next. It went off regularly, about twice per second. You know when you get a double or triple knocker after beating multiple replay levels? It's like that but constant.

#9 1 year ago

i have the same issue with my lethal weapon. it came with the wiring for the knocker and looked like there was one there before.gave up on trying to fix this problem...let us know if you fix this

#10 1 year ago

Do a factory reset.
Possible that the game is set up for Coin meter units, and the game - for some reason - is trying to advance the 'coin meter'. In WPC games, the coin meter used the knocker output.

#11 1 year ago
Quoted from Coyote:

Do a factory reset.
Possible that the game is set up for Coin meter units, and the game - for some reason - is trying to advance the 'coin meter'. In WPC games, the coin meter used the knocker output.

Huh... I didn't think of that. Will do a factory reset and see if that helps.

#12 1 year ago

Try removing and reseating the ASIC chip. This can cause weird things to happen if some pins don't connect correctly.

#13 1 year ago
Quoted from arolden:

Huh... I didn't think of that. Will do a factory reset and see if that helps.

Good luck. I'm kinda doubtful that's the actual issue, but if everything else checked out okay.. might as well try.

#14 1 year ago

you say it stops when you start a game? is there a relay somewhere that switches between flasher and coil? that might not be working..

#15 1 year ago
Quoted from tonycip:

you say it stops when you start a game? is there a relay somewhere that switches between flasher and coil? that might not be working..

Not in a FT. It's a WPC game. There might be a short, though. Have you tried running through flasher test to see if anything there causes the knocker to fire?

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