Transistor blowing, how do you check coils again?

Spbeyond

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Hey guys, I may have been stupid here. There is a transistor on this stern I am working on and it was blown so I replaced it. I thought It was for the scoop so I replaced that coil because I thought it tested out bad (at 003 and the beeper going on the dmm with the diode cut). Put it all back together and it played good, for a few minutes, then the fuse blew. I tested the transistor again and it was bad again. I figured hey I must have messed up the install so I cut it out and replaced it. and the game played again right until the ball hit one of the pop bumpers the the fuse instantly blew and the transistor went again.

So can a bad coil blow a transistor? Once I realized it had nothing ot do with the scoop I noticed the paper on that coil looks burnt. Cut the diode and it tested at 003 with the beeper sounding on the DMM. I thought that meant bad but I cut the diode on another know good coil and it tested at 004. Am I doing this wrong? I thought a good coil would test out much higher.
 
Since the coil looks like its been REALLY hot do you think its probably toast?
 
Since the coil looks like its been REALLY hot do you think its probably toast?

Depends. I would check the coil diode and if it's shorted and the coil is reading close to the other pop bumper coils and the plunger travels smoothly through the coil sleeve I would replace the coil diode and try it. If it's working fine I would probably leave the coil. It would also depend on how burnt it looks. If just the paper has gone brown that's one thing. If the bobbin or windings looks melted that's another story.

Ultimately it depends if there are shorted windings. I would think that a coil that reads 3 ohms with the other pop bumper coils reading 4 ohms wouldn't instantly cause the transistor to blow.

Anyway... did you check the coil diode?
 
I replaced it (the diode on that coil), still blows. EF

The coil doesn't fire, and the fuse and transistor will blow immediatly upon the ball hitting that pop bumper. I have another coil, you think I should throw it in?
 
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I replaced it (the diode on that coil), still blows. EF

The coil doesn't fire, and the fuse and transistor will blow immediatly upon the ball hitting that pop bumper. I have another coil, you think I should throw it in?

Sure it wouldn't hurt to try the new coil. Just be sure your coil diode is installed with the correct polarity.

Before that I would try it with that coil completely disconnected. Could also be a short somewhere else. If you can close that pop bumper switch (during game play) with the coil disconnected and it doesn't blow the fuse or transistor you know the problem is isolated to either the coil or coil diode.
 
I don;t know what game you're working on ... however the basics ......
If a coil tests below 3ohms (3 is quite iffy IMHO) it's basically shorted - get rid of it. And to answer your question - absolutely a bad coil will blow a transistor.
I'm not sure how your DMM reads out but mine would show 4. <-- notice the decimal point is AFTER the 4. If your reading is .004 it's toast.

Test the transistor itself - put DMM on Ohms buzz mode and put one lead to the TIP of the transistor and another to a ground point on the board. If it buzzes your transistor is toast.

If there's any burn marks/browning on the coil wrapper get rid of it.
 
Thanks guys! Seriously if your ever in utah drinks are on me! The crazy thing is my DMM doesn't show a decimal place when your measuring ohms. Might be why Im messed up. I figured that ment .003 ohms but maybe its 3.0
 
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Thanks guys! Seriously if your ever in utah drinks are on me! The crazy thing is my DMM doesn't show a decimal place when your measuring ohms. Might be why Im messed up. I figured that ment .003 ohms but maybe its 3.0

If the good coils are reading 004 you can assume it's not .004. If it's not an auto ranging meter it can read like that depending on the scale it's set for.

I thought that meant bad but I cut the diode on another know good coil and it tested at 004.
 
Freaking tested just the switch on the pop bumper without the coil, nothing blew. Put a brand new coil/diode on it and it blew the fuse and resistor. Also another pop bumper and scoop doesn't work. its crazy. I am out of ideas on why that is blowing.
 
Freaking tested just the switch on the pop bumper without the coil, nothing blew. Put a brand new coil/diode on it and it blew the fuse and resistor. Also another pop bumper and scoop doesn't work. its crazy. I am out of ideas on why that is blowing.

Are you triple sure that you installed the coil diode with the correct polarity? The banded side of the diode will go to the positive side of the circuit.
 
It doesn't hurt to check your wiring at the board as well, and you may as well check that diode you installed and make sure its ok. Check your voltage too, make sure its not out of spec somehow. Dont forget to check the board diodes, if you have them.
 
The thicker wire (yellow) should be toward the band right? thats how it was. I will have to recheck everything!
 
You've got some kind of wiring problem, something's shorting out somewhere. It's got to be right there at the coil, or it would do it as well when you pressed the switch but had the coil disconnected.

You said it blew the resistor, you mean the transistor? Keep in mind that on many boards, there is

1. a transistor
2. a pre-drive transitor
3. an IC chip

If ANY of those are bad, it'll blow fuses, and eat up transistors, lock on coils, etc.

My guess would be your predriver transistor is bad as well.
 
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