How to test a power pack

[danray35e]

Im a little confused as to the proper way to do this. I read the manual but its talking about neon lights and other things I don't have. I have a multimeter. Can I do it with that?

Its a 76 johnson 55hp I only have spark on one cylinder. First thought was coil. So to check coil I switched them. Now the coil that wasnt firing is firing. So now I am at the power pack. I understand it has to receive a signal to switch from coil to coil so I suppose it could be that it is not getting the signal to switch. Not sure how to proceed at this point. without the neon lights to test with.

 

[Joe Reeves]

Re: How to test a power pack

Forget the neon light test as it's very unlikely that oyu'll ever track one of those things down, and it's not needed anyway.

You have successfully proven that both coils are good. This leaves the powerpack and timer base sensor.

There is only one timer base sensor on that model and if it fires one coil, it is okay and should fire the other coil UNLESS the powerpack is faulty... OR... perhaps the timer base sensor wire leading to the non firing coil is broken or shorting somewhere.

Check the timer base sensor with a ohm meter at the powerpack for a proper reading. Disconnect the wires from the powerpack first of course.

If the timing base sensor is okay, that leaves the powerpack. Not difficult to trouble shoot that system.

 

[danray35e]

Re: How to test a power pack

Forget the neon light test as it's very unlikely that oyu'll ever track one of those things down, and it's not needed anyway.

You have successfully proven that both coils are good. This leaves the powerpack and timer base sensor.

There is only one timer base sensor on that model and if it fires one coil, it is okay and should fire the other coil UNLESS the powerpack is faulty... OR... perhaps the timer base sensor wire leading to the non firing coil is broken or shorting somewhere.

Check the timer base sensor with a ohm meter at the powerpack for a proper reading. Disconnect the wires from the powerpack first of course.

If the timing base sensor is okay, that leaves the powerpack. Not difficult to trouble shoot that system.

Is this the coil you are referring to for me to check?
Test No. 3
Sensor Coil Low Ohm Check

Test No. 4
Sensor Coil High Ohm Check

 

[F_R]

Re: How to test a power pack

That would be the tests. However, the one sensor triggers both cylinders, so if one works the other should also. Same goes for the wires. So how does it know which cylinder to fire? By the polarity of the signal from the sensor. A positive pulse fires one cylinder, a negative pulse fires the other cylinder. Same sensor, same wires.

OK, I suppose it COULD be a problem with the gap or something, but that is so unlikely. I'm afraid you have a bad power pack.

BTW, the modern way to test that stuff is with a DVA meter. The neon tester is so old school. And no, an ordinary multimeter won't get it.

 

[danray35e]

Re: How to test a power pack

That would be the tests. However, the one sensor triggers both cylinders, so if one works the other should also. Same goes for the wires. So how does it know which cylinder to fire? By the polarity of the signal from the sensor. A positive pulse fires one cylinder, a negative pulse fires the other cylinder. Same sensor, same wires.

OK, I suppose it COULD be a problem with the gap or something, but that is so unlikely. I'm afraid you have a bad power pack.

BTW, the modern way to test that stuff is with a DVA meter. The neon tester is so old school. And no, an ordinary multimeter won't get it.

Thanks so much for that informative explanation of how it figures out which coil to fire. I kept imagining a switching signal from under the flywheel where perhaps the mechanism telling it to switch was faulty, but now i get it. one coil sensor, one wire and the switching mechanism is the polarity changes as the magnets pass. I am an electrician but not used to thinking in terms of dc. I have a dva but was not sure how exactly to to set it for what I was going to read.

 

[OLDIRON]

Re: How to test a power pack

On that motor, if you get fire on only one cyl. And both coils prove to be good. It's 99% sure the powerpack is faulty. By the way, a DMM, or a VOM is not a DVA. Without a DVA, you won't get true voltage reading. Replace the powerpack and she'll throw a wicked spark on both cyls.