Older Jet DC Motor Problems

[Jonathan Tuttle]

My trusty JSL-10TS motor is having problems.


First, some background. I was given the saw missing the power switch & thermal cutoff assembly. I wired in a simple power switch from a Craftsman saw. So, no thermal cutoff in the circuit. I have also disassembled the motor twice and blown out everything. The brushes look fine, but I've ordered a new set anyway. I've looked at all the wiring and it's fine as well. At the time I did all this, I thought it was an AC motor. Jet tech support informs me it's a DC motor. Normally, I'd expect to see a rectifier circuit somewhere, but I don't see one on the saw or in the parts diagram. Am I misinformed? This is my first DC motor. Would a DC motor even run on AC current?


Anyway, the problem is this: occasionally, maybe once a week or less, when I start up the saw is starts to spin for a fraction of a second, then dies. Just like a popped breaker, but it's not that. If I spin the blade with a piece of wood, it'll stutter for a few seconds and then run normally about half the time. I've tried rotating the blade with the power off before starting it again, but that does nothing. I've also tried different 120v circuits in the house, but it's the same in all of them.


The first thing I'd normally look at would be the starter capacitor, but I don't see one on the parts diagram or under the hood -- I guess DC motors probably don't need starter capacitors. The thermal cutoff would be my second suspect, but there isn't one.


Can you electrical gurus shed any light on this problem? I love my saw and I'd hate to get rid of it!

[Dan Friedrichs]

It looks like this is a "universal" motor (the kind you'd find in a router, etc), not an induction motor.

"Universal" motors are called such because they can be ran on either DC or AC (theoretically - in practice, there are differences in how they are designed). So tech support was not "wrong" to tell you that it's a "DC" motor, but there is no rectifier - it runs on 120VAC.

That said, it's not an induction motor, so it doesn't have a start capacitor.

What you're referring to as a "thermal cutoff" is just a circuit breaker. It's fine that you don't have it.

Replacing brushes is a good first step. Those are the only moving parts.

[Jonathan Tuttle]

Thanks Dan! I'll follow up after I get the new brushes put in.

[Jonathan Tuttle]

Hi Dan. I got the brushes in and it seems fine. Fingers crossed it stays that way!

[Dan Friedrichs]

Good to hear! Those are really the only moving/servicable parts, so the good news is that if it stays fixed, they were likely the problem, and if it breaks again, you know there is nothing else that can be done