EX21 motor going out

[Mimi]

It has been a while since I have been on here. I haven't been out in my shop too much because the motor on my saw is going out. It has a dead spot in it. when I adjust the speed it will just stop. I am trying to figure out  how hard it is going to be to just replace the motor.I know some of you have probably done it. is it easy and I know it will be worth it.

[Jim Finn]

It might be the speed controller that is the problem, no?.

[Lucky2]

Mimi, how sure are you that it's the motor giving you problems, are you sure it isn't the variable speed control switch?

Len

[Phantom Scroller]

Try the motor brushes or the plug in the back is in properly. Roly

Edited June 2, 2016 by Phantom Scroller

[Mimi]

I changed the control panel and still does it.  It is plugged in proper. I called Seyco and told them what it was going and they said it sounds like the motor. Not sure how to check the brushes

.

[CharleyL]

To test the motor you are going to have to unhook it's leads from the saw electronics, then connect an ohm meter to the leads. Very slowly turn the motor shaft and note the ohm readings. Since the brushes are touching segments of the motor commutator there will be a drop in reading each time the brushes cross a gap between the segments, but the readings on the segments should be approximately the same. If there is a "dead spot" where the ohm reading goes very high in resistance then the segments of the commutator that the brushes are touching have an open winding connecting them. With the motor in this position, remove the brushes and look down the brush hole with a flashlight. If the brushes are visibly damaged or the bottom of the brush hole (the commutator segment) is visibly damaged, then this is likely the problem. The brushes are behind the 3/8 diameter black plastic covers on two sides of the motor opposite each other. There is a spring behind the cap, so be careful when removing. At the other end of the spring is a black carbon brush. The brush is square sides and the bottom end will have a curved shape. It should be at least 1/2" in length (it wears away and becomes shorter as the motor runs. New brushes are easy to replace, but be certain to always replace a used brush with the curved end the way that it came out. The curve should match the curve of the motor rotation.  A damaged commutator or open winding inside the motor will require motor replacement. 

 

If you replace the brushes, do the test over again to be sure that you don't also have a damaged commutator or open winding. The motor should have approximately equal resistance at each segment as you slowly rotate the motor. Variations of a few ohms

at each reading will not affect the running of the motor. A very high reading compared to the rest will affect the running of the motor. 

 

If you can, it's a good idea to blow out the motor with compressed air before you put it back on the saw (wear eye protection). As the brushes wear, tiny pieces of their conductive material will settle in the bottom of the motor and could cause motor damage later on, if not removed.

 

I haven't worked on an EX. But the design is very similar to my DeWalt788. With it, the side cover opposite the motor must be removed. You probably have already done this to be able to disconnect the motor wires for the test above. If not, follow them to their connection point and disconnect them. Be certain that you can return each wire to it's correct terminal by labeling one wire and it's connection somehow (a piece of tape on one wire and it's connection)or some other method). If connected opposite, the motor will run backwards. This doesn't matter on a DeWalt, but might on the EX.

 

Then the bolt in the end of the motor shaft must be removed to separate the shaft and eccentric from the motor shaft. After it is free from the motor shaft, you can then remove the bolts that hold the motor case to the saw. It's not that hard to do, but keep track of the pieces removed so you can replace them correctly later.

 

Charley

Edited June 2, 2016 by CharleyL

[WayneMahler]

Charlie has a great point. This works as long as you  have the equipment to test. If have access to an ohm meter it would best for a digital. Watching a needle sweep on an analog may mislead you as you turn the motor over. Keep us posted on the progress you make please. 

[CharleyL]

Actually, I prefer an analog meter for this, but a digital meter will work.

 

You don't actually need the exact ohm meter readings, just the trend. As you slowly turn the motor shaft you will get short high readings as the brushes cross the insulation between the commutator segments, and then the meter should return to an approximate same ohm reading as previous segments, as the brushes ride over the segments of the commutator, then another short high reading, followed by another approximately the same lower reading. What you are looking for is a place where the ohm reading goes very high and stays that way longer than it does when crossing the short space between the segments.  If you don't get a long high reading, that's wonderful, because it means that your motor is OK. A long high reading indicates trouble, and you have to proceed further to find out exactly what it is.

 

 

Speed control problem-

 

The speed control can be diagnosed in a similar manner, if you suspect that it is bad, but it has to be disconnected from the saw's electronics to do this. On a DeWalt 788 there is a small connector in the three wires running to the  speed control about 4" from the speed control. Unplug the connector and you are ready to test.

 

There are three connections on the speed control. Using an ohm meter, connect one lead to the center terminal and the other lead to either end terminal. Now, slowly turn the speed control shaft. The ohm reading should slowly increase or decrease, depending on which end terminal that you connected to and which direction that you turned the shaft. If you find spots during the slow rotation that the ohm meter jumps around, or it stays at a very low or very high reading, the control is bad. You should also test by putting the leads on the two end terminals of the control. This reading should be steady, and on the DeWalt 788 it should read 50,000 ohms, or very close to it. I'm not sure what the reading for an EX saw is, but it will likely be the same.

 

If your speed control is bad, DeWalt wants to sell you a complete speed control board including the speed control. Radio Shack, or another electronics parts supplier can sell you a 50,000 ohm (linear taper) potentiometer (what they call the speed control) for about $1.85. Radio Shack carries one at a great price, but the shaft is too long and is round instead of having a flat on one side. I have used these as a replacement by using a hack saw to cut the shaft to length and a file to make a flat on the shaft. Be sure to turn the shaft of both the old and new controls to the same end stop and file the flat in the same position or your numbered speed knob will not be the same speed for a given number setting. Test the knob to see if the flat is enough for the knob to fit.

 

Now, un-solder one wire from the old speed control at a time and solder it onto the same terminal of the new control. Do this 3 times using a low wattage (about 40 watt) soldering iron and "Electronic Solder" and you can install this new control in your saw. Plug the 3 wire connector in and test your saw for speed adjustment, then un-plug the saw and continue re-assembly.

 

Harbor Freight sells a digital multi meter with several ohms scales for less than $6.00, and sometimes gives them away free with any purchase if you catch the right one of their weekend sales. I have about 8 of them scattered around my house and shop. They are quite accurate and will do this job, and many other electrical jobs around the house and shop quite well, so it's a good idea to have one if you don't already. You can't loose at $6.00, or even better if you can get one free.

 

Charley 

Edited June 2, 2016 by CharleyL

[Mimi]

Thanks for the information. I will get with a neighbor down the street and see if the can help me with this. I am not really good with electronic. will let you know what happens. 

[Lucky2]

Good luck with it Mimi, hopefully, the repair is a cheap one.

Len

[CharleyL]

Mimi,

 

If you can find an ohm meter or a multi meter and can't get help using it, send me a PM.

I'll work with you by PM, e-mail, phone, or whatever, to help you diagnose your problem.

 

Charley

[Ron Johnson]

It's possible the brushes on the motor are worn and need replacing Mimi. Unscrew the caps on each side of the motor, unscrew the brush and visually check. You can tell just by looking. To replace may cost $20.00 each. I've replaced mine twice in the last 16 years which only takes a few minutes. The brushes should be available through Seyco or order them through a local electric outlet which I had to do. I now keep a spare set on hand eliminating any shut down time. Good luck.

[Mimi]

Well i pulled the brushes and they are not flat on the end . They are curved. I guess they can be bought at a hardware store .could this cause the problem. I could replace them and see how it goes.

[JustLarry]

Mimi - the brushes are curved so they can make good contact with the armature.

 

Larry

[CharleyL]

Mimi,

 

The curved end is OK. It's the length and general condition that is important. From the curved end to the spring should be a minimum of 3/8-1/2".  If less than that, replace them. New brushes won't have the curve. They wear that way when used. When you put a "still good" used brush back in make sure you orient it so the curve follows the rotation of the motor. When facing the back end of the motor, install the brush with the curved side of the brush facing you. You can actually use a shorter brush, but plan on replacing it with a new one very soon. If you let them wear until the spring touches the commutator, the motor will be ruined, and scroll saw motors are extremely expensive. 

 

Charley

[Mimi]

sorry it has been a while since i have been on here. I finally got my saw fixed it was not the motor after all thank goodness. I called Ray at Seyco and he diagnosed the problem and sent me the part. It was just the speed control after all. So saved a bunch of money and time. Now am taking the craftsman off the stand and putting my Excalibur back where it belongs and going to buy me some wood and get to cutting.. I am very proud of my self for installing the part myself. Now got to go get some work done. Thanks everyone will post some finished work 

[dgman]

Great to hear Mimi! Looking forward to seeing some pictures of your completed projects!

[amazingkevin]

Incredible info never seen in ssv ,amazing what will turn up when you nee it,Thanks !

[CharleyL]

That's very good news, Mimi.

 

But now we want to see what you make with your repaired scroll saw. Please post some pictures.

 

Charley