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Thread: Dewalt 925 motor problem

  1. #1

    Dewalt 925 motor problem

    Hello All,


    I am new to the forum, pardon any misspeaks. I have the Dewalt 925 that was in my father's basement workshop when I was a child. I am certain he bought it new around 1960, when that house was built. It did not see heavy use as he was a physician. It remained in the shop until the 1990's, when he gave it to a woodworking cousin. The cousin downsized two years ago and offered it to me. I, of course, jumped at the chance to acquire this saw that had been the center of many great memories.
    I have used it only occasionally for home projects. Last summer, while using it to cut a thick piece of wood, it was bound up and stalled. After that, it would not 'spin up'. It would slowly turn until it kicked the circuit breaker (only once). During disassembly I discovered that the felt washer in the brake assembly had disintegrated, so I removed it. The saw worked fine after that, but without the brake it took a long time to spin down. It then sat unused until this summer. My grandson had a project requiring making two cuts on 1/2" plywood, 8" and 10". After making the 10" the saw again would not spin up. Again disassembling it I discovered one of the brake springs was loose in the brake. All of the springs were stretched and distorted, so I removed the entire brake assembly, including the friction plate (i.e.: there is nothing between the motor and bearing. This did not fix the problem. The motor spins freely by hand, but still only turns slowly when turned on, until it kicks the circuit breaker.


    Sorry for the lengthy post, I am just trying to provide as much data as possible.
    Any assistance will be greatly appreciated.


    Thank you,
    Roy

  2. #2
    Join Date
    Aug 2020
    Location
    St. Albert, Alberta, Canada
    Posts
    68
    It sounds like the run winding isn't getting power.

  3. #3
    Quote Originally Posted by Bill Yacey View Post
    It sounds like the run winding isn't getting power.
    Bill, Thanks for the reply. How do I check that? BTW. I have all of the original documentation that came with the saw, including a hard copy book that I guess my Dad bought that shows everything that can be done with the saw.

  4. #4
    Join Date
    Aug 2020
    Location
    St. Albert, Alberta, Canada
    Posts
    68
    If you open up the motor, you will find a set of start contacts on one end of the motor shaft. These contacts must be closed when the motor is at rest, and open up when the motor comes up to speed. Take the UNPLUGGED AC line cord and clip the leads of a multimeter to the hot and neutral blades of the plug, set your meter to read resistance.

    Turn the power switch to the on position and note what it reads; then manually open the start contacts and see what the meter reads. It should read a fairly low resistance with the start contacts open, a few ohms. If it doesn't read anything, check the resettable circuit breaker for continuity, or for loose wires inside the motor. Some induction motors have a thermal circuit breaker embedded inside the windings; these can go open which renders the motor scrap, unless you can get at the leads from the breaker to bypass it.

    Edit: I'm not familiar with this particular motor. Are you sure the "brake" you disassembled and removed wasn't the centrifugal weight and spring assembly for the start switch contacts?
    Last edited by Bill Yacey; 09-12-2020 at 1:04 PM.

  5. #5
    Quote Originally Posted by Bill Yacey View Post
    If you open up the motor, you will find a set of start contacts on one end of the motor shaft. These contacts must be closed when the motor is at rest, and open up when the motor comes up to speed. Take the UNPLUGGED AC line cord and clip the leads of a multimeter to the hot and neutral blades of the plug, set your meter to read resistance.

    Turn the power switch to the on position and note what it reads; then manually open the start contacts and see what the meter reads. It should read a fairly low resistance with the start contacts open, a few ohms. If it doesn't read anything, check the resettable circuit breaker for continuity, or for loose wires inside the motor. Some induction motors have a thermal circuit breaker embedded inside the windings; these can go open which renders the motor scrap, unless you can get at the leads from the breaker to bypass it.

    Edit: I'm not familiar with this particular motor. Are you sure the "brake" you disassembled and removed wasn't the centrifugal weight and spring assembly for the start switch contacts?
    Bill, Thanks. I suspect you have hit the problem on the head. I thought that assembly was the brake slowing the motor when power was cut. Where can I get replacement springs for the assembly?

  6. #6
    Join Date
    Aug 2020
    Location
    St. Albert, Alberta, Canada
    Posts
    68
    I honestly have no idea. Perhaps ask around the forums to see if someone has a motor for parts?

    Depending on how the centrifugal mechanism fastens to the shaft, you could probably use one from another motor with the same shaft size and motor speed. I'm assuming the motor is a 3450 RPM?
    Last edited by Bill Yacey; 09-13-2020 at 10:06 PM.

  7. #7
    Quote Originally Posted by Bill Yacey View Post
    I honestly have no idea. Perhaps ask around the forums to see if someone has a motor for parts?

    Depending on how the centrifugal mechanism fastens to the shaft, you could probably use one from another motor with the same shaft size and motor speed. I'm assuming the motor is a 3450 RPM?
    Bill,

    Mine is a 3425 rpm. I don't think it matters. I suspect I have fried windings. See what you think:

    Saw50.jpg

    Roy

  8. #8
    Bill,

    Do you have any idea where I can get a replacement motor and how much it should cost. Mine is a 235 frame.
    SawModelPlate.jpg

  9. #9
    Join Date
    Aug 2020
    Location
    St. Albert, Alberta, Canada
    Posts
    68
    It looks like it got pretty warm. Anytime an induction motor doesn't come up to speed within 1 second after turning it on, there's something wrong and should be immediately switched off until the problem is rectified, or else you wind up with burnt windings.

    I'm not sure where you might find another motor. As I mentioned, I would inquire around some of the vintage tool forums.

  10. #10
    DeWalt RAS forum, or Facebook vintage RAS group. Or buy a donor saw off Craigslist or Facebook marketplace. Or buy a better saw and use your saw for parts. Lots of RAS’s out there. I wouldn’t have that motor fixed unless it was the only option.

  11. #11
    Join Date
    Jun 2017
    Location
    Landenberg, Pa
    Posts
    361
    Come to the Delphi DeWalt RAS forum, we’ll find you a frame 235 no problem.

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