Delta Unisaw Switch

[GreggH]

Hi.  I'm a new member but have been a browser numerous times over the years.  Now I need to ask my own question so I have to drop the pretense of anonymity.

I have a 3hp Unisaw that is about 15 years old.  It has worked fantastically to this point.  Today the power switch froze in the ON position.  I can push the Stop button and disengage electricity but as soon as the Stop is released, the saw starts back up.  I have unplugged it and the situation repeats when replugged.  I removed the switch cover and one can see the three reddish buttons pop in on their own when the Stop button is released.  There is a little bit of blackening around the screw and wire engagement contact (1L1) where one wire of the 220 power goes out of the On switch.  I'm not sure if the black was present before this started, appeared when this started or is due to me performing multiple On/Off cycles to determine if something stuck could be unstuck.  Both the On and Off buttons on the controller depress easily and freely with no grittiness.

I refound this forum with a search but the only semi-relevant thread had the opposite problem of a saw not turning on.  So I ask for help......

[TDKPE]

Sounds like the contactor is stuck closed, or at least the auxiliary contact is.  Both the auxiliary contact, and the 'stop' button contact, are closed when the saw is running.  When the 'stop' button is pushed, it breaks the small circuit that energizes the coil on the main contactor and the contactor opens.  

Releasing the 'stop' button reestablishes that part of the circuit, but the auxiliary contact (mounted to the side of the main contactor), if it's stuck closed, allows the coil to become energized again, pulling in the main contactor.  The auxiliary contact and the 'stop' button are connected in series, so either one of them being open deenergizes the coil. The 'start' button loops around the aux contact to close that circuit which closes the main contactor, which in turn pulls the aux contact closed to hold the coil energized once the 'start' button is released.

You need to find that aux contact and examine it for damage.  Or there might be a short in the small gauge wiring that's part of the coil circuit, of which the 'start' and 'stop' button are also included.  But I'm guessing the aux contact is stuck closed.

[GreggH]

Sounds like the contactor is stuck closed, or at least the auxiliary contact is.  Both the auxiliary contact, and the 'stop' button contact, are closed when the saw is running.  When the 'stop' button is pushed, it breaks the small circuit that energizes the coil on the main contactor and the contactor opens.  

Releasing the 'stop' button reestablishes that part of the circuit, but the auxiliary contact (mounted to the side of the main contactor), if it's stuck closed, allows the coil to become energized again, pulling in the main contactor.  The auxiliary contact and the 'stop' button are connected in series, so either one of them being open deenergizes the coil.  The 'start' button loops around the aux contact to close that circuit which closes the main contactor, which in turn pulls the aux contact closed to hold the coil energized once the 'start' button is released.

You need to find that aux contact and examine it for damage.  Or there might be a short in the small gauge wiring that's part of the coil circuit, of which the 'start' and 'stop' button are also included.  But I'm guessing the aux contact is stuck closed.

That was it exactly.  I only had to wait to try it until the Cardiac Chiefs could hang on.

Thank you much!

[TDKPE]

That was it exactly.  I only had to wait to try it until the Cardiac Chiefs could hang on.

Thank you much!

Stuck aux contacts?  

We may meet again, as Buffalo is my neck of the woods out here in western NY.  
  I can’t believe how many folks are walking around in Bills gear.  They’re usually treated like lepers. 

[Lumber Yard®]

Tom knows his stuff. The Unisaw from that era (I also own one) have issues with the cheap mag switches. You might find it less of a headache to just order another cheap replacement.