Re: Dead Miter Saw: electrical ?

[Crater]

Here's one for the electrical among us. . .

> >Last week I was going to make a cut on my Hitachi Miter saw: I pressed >the trigger lock release and hit the trigger - as the saw came on, my >finger slipped off the trigger, and I immediately hit the trigger again. >Bad things happened. I blew the fuse at the panel, so I put a new one >in, and tried again: a little "rwhirrr" from the saw and the fuse blew >again. Dead saw. I have already bought another saw, but I want to fix >the other saw if possible. Can anyone offer a diagnosis? Thx. > >Kim

Most likely the switch has seen its day. Most problems I run into have been power cords.. this is still a possibility as well.

[Wilson Lamb]

Too easy. I don't see how the switch can blow a breaker, unless a wire falls off and shorts to the other side of the line.

Hitting the switch while the saw is coasting shouldn't cause any more current surge than starting from stopped. In fact, the surge will be reduced, so I don't see why your action should have caused the problem.

I'm not sure how that motor is wound, but if it is a compound winding, with the field in parallel with the armature, a bad brush contact would do what you report. If it's series wound, all current must go through the brushes and a bad brush would cause complete deadness.

The symptom is typical of shorted turns in the winding. That's a random occurrence and probably means curtains, since parts are so expensive. Repair would consist of either replacement of the field assembly (stationary windings) or the whole motor.

[Bob S.]

Don't all these type saws have the electrical brake on them ? When the switch is released it disconnects the power from the mains but then uses the EMF (if that's the correct term) of the motor windings to charge a capacitor or some kind of reverse winding to apply a reverse current flow to stop the blade. So a bad switch is a real possibility and/or a bad cap (or other device) used in the braking mechanism.

Bob S.