Tablesaw Troubleshooting Help

[Dave Richards]

A friend of mine asked me to look at his tablesaw to see why it won’t run. It’s a Jet cabinet saw wired for 220V. He thought it was the switch so he bought a new one from Jet and installed it matching the locations of the wires. It still doesn’t run.

I poked around this evening and discovered that if I push the relay in manually—with a stick—the saw will run just fine. Based on that, I rule out power supply and motor. Pressing the ON switch doesn’t do anything. It appears that the relay coil is not being energized.

The momentary contact switch that is depressed via the green button appears to be good. I get continuity through the switch when the button is pressed.

The lower section of the assembly—the stop portion has me a little stumped. There is a small wheel that appears to set a tripping current level for a breaker. Below that is a small plastic knob which has settings marked Test, Manual and Auto. It seems that this must break the circuit to the coil when the red button is pressed. What I can’t tell is which position it should be in for normal operation. The new switch came with that dial in the Test position which is adding to my confusion.

Anyone have any thoughts? There’s little in the way of information included with the switch. The wiring schematic is almost impossible to read. I’ll look closer when I can get to work where I have a lighted magnifier.

I don’t want to have to stand there with a stick holding the relay in so he can use his saw. Help? Anyone ever seen this before?

Thanks.

Dave

[Todd Willhoit]

Dave,
I guess this is my initiation to SMC. I have been lurking for a while, but no posts.

I am not familiar with the Jet circuit, but I do know a bit about motors and motor protection. The "breaker" you are looking at is probably an overload (OL) relay. The plastic knob has three functions: 1) Test - trip the relay to see if it works (Similar to the trip button on the GFCI in your bathroom/kitchen.), 2) Manual - the relay requires a manual reset in the event of an overload, and 3) Auto - the relay automatically resets some length of time after the overload. This "time", being the time required for the bi-metallic strips in the OL relay to cool and move to the normal position.

From your comments, I assume the saw is using a 120V control circuit with a motor contactor (really big relay). If this is the case, the circuit usually has the start and stop switches and a set of normally closed contacts from the OL relay in series with the coil of the motor contactor, and an auxiliary contact from the contactor to seal-in around the start switch. If the OL has tripped, or a wire has become loose, the circuit cannot energize.

With the start button depressed, you should be able to verify continuity from either side of the start switch to the contactor coil, and across the coil itself. If you don't have continuity, try to reset the OL and check for loose wires. If you have continuity, look for a blown control power fuse, disconnected ground wire, or open circuit in the contactor coil.

If you are able, please scan and post a picture of the schematic. I am sure there is a simple explanation to the problem.

Best of luck!
Todd

[Cecil Arnold]

I wish I had an answer, and I apologize if it seems I'm hijacking the thread, but I have the same problem on my new MM16. It seems there is no power to the magnetic coil that allows the switch to function. Like you, I've run contineuity(sp) test on all the over rides etc, and installed a new switch. The tech keeps telling me that he could fix it in only a few minutes once he gets here (next Wednesday). It's become a personal challenge, but so far nothing I try seems to work. I'll keep watching this thread, and if I learn anything will pass it along in the hope we both can overcome the electric grimlins.

[Martin Shupe]

Cecil,

Check the "push button" kill switches on the top and bottom doors of you MM-16. My door hinges got loose, so the button was not depressed far enough. Whenever I started my saw, it would start for just a moment, then the kill switch would stop it. That might be your problem.

[Jim Becker]

David, you or your friend can call the Jet "Tool Doctor" at 800-JET-TOOL (800-538-8665) to get assistance with this problem. The switch on a Jet cabinet saw (3hp) is a magnetic switch and will not function if the electricals to the saw are not properly working right. Do a "stupid thing" check by inspecting the plugs, cords and outlet to be sure all conductors are where they are supposed to be and there is no damage to them or the cord. If this does not show you anything, you may actually have an issue with the motor if the relay is tripping and keeping the machine from firing up. Call Jet for more assistance.