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(Topic ID: 124547)

LW3 Beacon won't stop spinning. Any ideas?

By action76

5 years ago

Topic Stats

  • 14 posts
  • 5 Pinsiders participating
  • Latest reply 5 years ago by snyper2099
  • Topic is favorited by 1 Pinsider


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#1 5 years ago

I picked up a LW3 with a few problem I have been working through. One that has me stumped is that the topper beacon spins continuously from the second it's powered on. I changed Q25, which I believe controls the beacon, because it tested bad. I thought that would fix it but it didn't. The pre-driver tests fine, so I am not sure where to go from here. I guess it could be a TTL chip or PIA? Anybody have this problem before or know how to fix it?

Also, it had a pop bumper stuck on and melted the coil. I replaced the coil and the Q9 and the pre-driver which is a 2N4401. I did not have a 2N4401 so I used a 2N2222A because I read somewhere they were compatible. Well the PB coil does not lock on now but it will not fire at all. Do you think the sub transistor I used would be the problem?


#2 5 years ago

probably riggs was driving last.

#3 5 years ago

Pre driver 2N4401 can test good but still be bad... swap it out first. They are like $1. I would order 10 of them since they fail ALL THE TIME. In pinball, they are more like fuses than transistors.

On the other question... I would swap a known working 2N4401 from another place on the MPU to test your theory, if you don't have a new one readily available.

2n2222a? I've never tried one of those in a pinball. It's not identical but should be ok... nope, legs don't match!

#4 5 years ago
Quoted from action76:

I did not have a 2N4401 so I used a 2N2222A because I read somewhere they were compatible.

While the spec's are similar the packaging is completely different. So even if it might work I would guess you've got it wired incorrectly. 2N4401 is 1-emitter, 2-base and 3-collector. 2N2222A is 1-base, 2-collector and 3-emitter.

Get the correct transistor and try again.

#5 5 years ago

Looks like you would have to mount it backwards for a 2N2222a to work. Good to know this. But,
I would just use the intended part as terryb suggested, not "cram" something like that in there.

#6 5 years ago

Backwards wouldn't work either (that would put the base on the collector and the collector on the base).

OP: Do not ever use a different transistor unless you are positive it is a valid replacement. You not only risk the transistor going up in smoke, but also damaging other components.

#7 5 years ago

well, assuming you twisted two legs to crossover as well... that's what I meant. I would never try to hack that part in there is all I was saying. I fixed my posts.

#8 5 years ago

Wow! I thought I checked that they were both EBC. I guess I read it wrong. I will try swapping that out with the right part and try again. Thanks guys. I'll report back when I try these suggestions.

#9 5 years ago

Update: I replaced the wrong transistor with the correct one and it did not make any difference. I also changed the pre-driver on the beacon just to make sure and it did not make any difference either. A friend helped me track it down and now it looks like a logic issue. I am going to swap out one of the 7402 chips and see if that fixes the pop bumper. I am not sure if that chip has anything to do with the beacon though.

#10 5 years ago

PIA on MPU drives the 7402's, which in turn drive the pre-drive trans, which in turn, drive the main trans. Usually a 7402 drives more than one device/transistor. It is possible for just one leg to short on a 7402.

#11 5 years ago

I'd leave the light always spinning. That's not a problem, that's a feature.

#12 5 years ago
Quoted from snyper2099:

It is possible for just one leg to short on a 7402.

Best I can tell, the chip is made up of 4 NOR gates and each one controls a coil. So it's possible that just one gate is bad and the other 3 are fine, I think.

#13 5 years ago

Well, the new 7402 chip fixed the non firing PB. Still not sure about the beacon yet though.

#14 5 years ago

Well, it could be the 7402 that runs the beacon. Probably a different one.

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