(Topic ID: 183115)

Road show diverter coil locked on *Fixed*


By lavmech1

3 years ago



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  • 12 posts
  • 5 Pinsiders participating
  • Latest reply 3 years ago by lavmech1
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#1 3 years ago

I had the playfield of my Road Show up to look at some bulbs (with the power off). When I closed everything up and switched on the machine I though I heard a coil lock on. I found the right rear diverter coil locked on and smelled burned. I've only owned this game for a couple of days so I don't know the machine's history. The closer I look at it though, the worse it seems. It's in rougher shape than I thought and now this happens for no apparent reason. Not cool. I need some help.

I looked for the transistor for this coil Q64 I think. Not burned up visibly. Not sure if it's worth trying to test that first. No voltage coming from the pin for the solenoid at the MPU connection J130 wire 6. There's about 71 volts coming into the solenoid plug (which I have disconnected to prevent locking it on-see the pic). The coil looks pretty bad. Lots of corrosion on this game. Could it be shorted internally or something? Can coils lock on when they fail? Any advice is appreciated. Thanks!

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#2 3 years ago

Use your DMM and test for continuity from suspect transistor tab to ground...if you get a beep then the transistor is bad. That transistor and it corresponding pre driver should be replaced.
Some people will replace the coil and diode as well...

#3 3 years ago
Quoted from cosmokramer:

Use your DMM and test for continuity from suspect transistor tab to ground...if you get a beep then the transistor is bad. That transistor and it corresponding pre driver should be replaced.
Some people will replace the coil and diode as well...

Great, that's easier than I thought on testing the transistor. I'll do that this morning. Also, there is NO diode on the coil. I saw that another diverter coil also had no diode. Should ALL coils have a diode as a rule?

#4 3 years ago

The tab of Q64 -a TIP36c- is already conected to GND so it will beep anyway.
To test this transistor for a short, unplug J130 and measure continuity from GND to J130-6 / J131-1

#5 3 years ago
Quoted from zaza:

The tab of Q64 -a TIP36c- is already conected to GND so it will beep anyway.
To test this transistor for a short, unplug J130 and measure continuity from GND to J130-6 / J131-1

Ahh, that would explain why I got continuity to ground from the tab of all of the large transistors (Q64,66,68,70,76,78,80). I'll have to test it the other way after work this afternoon. Thanks!

#6 3 years ago
Quoted from zaza:

The tab of Q64 -a TIP36c- is already conected to GND so it will beep anyway.
To test this transistor for a short, unplug J130 and measure continuity from GND to J130-6 / J131-1

Good to know, thanks...I tested tip 102 and 122 the other way with success...just when I think I know enough to help someone else I stick my foot in my mouth...
Sorry OP

#7 3 years ago

There is no continuity from ground (i used the braided ground wire in backbox) to any of the pins on J130 or J131. I checked at both the plug and the header because I wasn't sure which side you meant. So, if not a bad transistor should I look back at the coil next?

#8 3 years ago

So, I think I'm making progress. No short to ground along the wiring harness and the transistors test ok. But the coil terminals themselves looked awfully close to the bracket it's held in. When I repositioned the coil lugs AWAY from the metal bracket the problem disappears! If I rotate the coil to where it touches the bracket I get either a distinct hum from something nearby or I get the hum AND the locked on coil. So, the coil is grounding out on it's own bracket. Problem now is I can't see how the coil is supposed to be other than the way it is now. It looks like it's mounted the way the bracket intends but how can this be if it's going to be so close to grounding out?!? I'll include pics of the coil when it's ok and when it shorts out. Maybe its in the bracket backwards?

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#9 3 years ago

The coil is backward.

#10 3 years ago

Awesome. Yes, I just found the diagram in the book. Now I'm wondering do I have to reverse the wires when I rotate the coil so it pulls the right direction?

#11 3 years ago
Quoted from lavmech1:

Awesome. Yes, I just found the diagram in the book. Now I'm wondering do I have to reverse the wires when I rotate the coil so it pulls the right direction?

No.

#12 3 years ago

All fixed. Turned the coil around. Working perfect and no chance of shorting out against the bracket. I guess the moral of the story, as always, is to check the obvious things first. The problem was right there staring me in the face the whole time!!! Thanks to everyone who helped out!!!!

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