Unisaw electric problem

[Bob Vaughan]

I have a 2003 unisaw. As I shut down the saw I thought I heard a pop. I started it up again and the motor turned on and was spinning but the blade was very slow in turning. The blade rotates easily on the arbor and the belts are intact. Some searching yields opinions that it may be the start or run capacitor. Is it easiest to remove the motor then check and replace it? Any other tips? I haven't replaced one of these before.

A "pop" sound is likely one of the capacitors, but checking the centrifugal switch is a good idea if the capacitors seem good.  The problem is that all Unisaw motors are not the same.  Below are some of the newer Unisaw motors with the centrifugal switch contact points circled.

   

   

   

[SteveS]

I pulled out the capacitors and they seemed just fine; no bulging or smells. I haven't pulled the centrifugal switch yet.

I removed the spring clamp from the plastic fan shaft but it doesn't want to easily come off. How do you remove it without breaking?

[Bob Vaughan]

I removed the spring clamp from the plastic fan shaft but it doesn't want to easily come off. How do you remove it without breaking?

from this thread

http://owwm.org/viewtopic.php?f=1&t=31506&start=0

   

[John Mihich]

Are you sure the arbor isn't spinning but the blade is loose?  Or the arbor sheave sheared its key?  Or the motor sheave?  

I would start with manually putting some torque on the motor (unplugged, please
) while holding the blade with a stick of wood to see if the arbor sheave or blade is loose.  To check the motor sheave, you'll probably have to pop off the fan cover and hold the fan gently (don't bend or break it).  Pop the belts off and check the set screws, but be aware that there may be two set screws, or even one on top of another.  

It sounds odd that the 'pop' happened at shutdown.  Capacitors usually blow on start-up, and switches don't usually make any sound when they weld themselves together.  Unless it physically came apart as the motor slowed, but still, in a TEFC motor (sealed up), I don't know how much internal sound would get out, and it should still run at full speed with the run capacitor still intact, just have wimpy starting.


If one leg is open, you'll get nothing I'm afraid.  It's just a 2-wire (hot/hot) circuit; just at double the voltage of the common 120V (hot/neutral) circuit.  What comes in through one conductor goes back through the other, reversing direction every 0.0083 seconds (1/120s) at 60Hz.

I didn't know that.  I just assumed it needed a neutral.  I was studying to be an electrical engineer (50 years ago) and don't remember that.  Of course I didn't take my last year; changed major.  All the work we did was 110 or DC work.  In the Navy I know all lines were with a neutral and of course the whole ship was ground.  I guess I am not too old to learn something new.

[TDKPE]

Here's a couple of schematics (sort of) of a 120/240V motor (no start winding or capacitors shown) that I made long ago, but they're clean enough to demonstrate the point.

At 120V, both motor windings are in parallel, but it could just be a single winding, or purely resistive load.  Connected between L1 and N, it drops 120V across the pair of windings.

   

At 240V, windings are in series (could substitute a single winding, or purely resistive load like a water heater element).  Connected between L1 and L2, the two together drop 240V.  No neutral needed.  Opening the circuit at any point will cut power completely, though parts can still be at 120V, hence the two-pole breaker with common trip.

   

At 240V plus small 120V loads, like a clothes dryer, the big current is between L1 and L2, but the small load like the motor, light, and control is across L1 (or L2) and N.  Those 120V loads are shown as being not part of the 'motor', but slide one down below the two-pole breaker and make it smaller (like maybe 5A) and it'll represent a clothes dryer rather accurately.

   

I'm showing + and -120V on L1 and L2, which is relative to ground/neutral, but of course, that polarity is reversing as is all the current directions every 1/120s on 60Hz power, and voltage peaks are actually 170V (times square root of 2 = RMS).  But I digress.

[SteveS]

Got the fan off but now at a loss of how the cover is removed. I loosened the four attaching bolts but cover won't budge. Tried tapping it with a hammer to see if it would come straight off or needed to rotate but nada. Couldn't find explicit directions regarding it.

   

[Bob Vaughan]

Got the fan off but now at a loss of how the cover is removed. I loosened the four attaching bolts but cover won't budge. Tried tapping it with a hammer to see if it would come straight off or needed to rotate but nada. Couldn't find explicit directions regarding it.

Pop on the end of the shaft with a piece of hardwood and a hammer.  The pulley end will drive out.

Go back and read that thread I linked to. The process is there.

[SteveS]

Thanks. I went through that web page but didn't know if it applied to newer motors or not.

[Bob Vaughan]

Thanks. I went through that web page but didn't know if it applied to newer motors or not.

The middle photo above should be similar.  Its an 83-651 Marathon made in the late 1990s.
Electric motor makers are constantly changing their designs to cut costs, so the Marathon-made motor you have maybe slightly different in some details, but the principles will be the same.

[SteveS]

I whacked on it fairly hard yesterday and it didn't budge. Is there anything to remove on the opposite side before driving it out?