Another Sears Radial Arm Saw Motor Problem

[mmcgo21680]

When attempting to power on the Sears RAS (circa 1977) set for 110V, it instantly throws the 20 amp dedicated breaker with no rotation or hum at all. The saw was working fine moments before the failure. I was just doing a couple of crosscuts (i.e.no extended hard cuts). Based on previous posts, here's what I've done so far:

1) tried the saw on another 20 amp dedicated breaker, same results (no extension cords in use) 2) took off the case, cleaned all saw dust out with a compressor 3) "sniffed" for burnt windings (no smell at all) 4) inspected all internal and external wires for nicks, scraps, pinches, etc, (wires look good) 5) Did a basic VOM test on the starting capacitor (seems to check out) 6) Reviewed the "breaking/starter" switch, points are a bit rough and I do see an arc at this point during testing. Is this arcing a symptom of bad windings, etc. or could the arcing itself be the source of thown breaker????

Any help greatly appreciated, Mikemcg PS..First post...Hope I followed proper protocol :)

[Nova]

(snip)

What does "seems to check out" mean? What readings did you get?

With the capacitor disconnected and with the meter set to the highest OHMS setting you should see a small kick of the needle and the reading should then go to infinity as the capacitor charges. If you get a resistance reading other than infinity once the capacitor is charged the capacitor is shorted.

[mmcgo21680]

[Charley]

If the saw trips the breaker without it's power switch on (like when you plug it in with the power switch in the off position), then the problem is NOT the motor. It's a short somewhere in the line cord, plug, or wiring leading to the switch.

[CW]

You have a short.

[mmcgo21680]

[Doug Miller]

No.

You tested only for a hot-to-neutral short. You didn't test for, and therefore haven't ruled out, a hot-to-ground short.

[MOP CAP]

What brand of receptical are you pluging it into? I had a similar problen several years ago after some ham handed carpenters doing some work at my house yanked theirplugs out at an angle and broke the plastic insulating material. When you then tried to plug another cord into the recpt. it would short and trip the breaker. The recpt's were Hubble.

Chuck P.

[mmcgo21680]

With the help of this usenet group and additional ideas, I have identified the problem. It indeed was a short to ground. There is "start switch relay" that had plastic standoffs on both sides of the relay tab as an insulation off of the frame (ground). Over the last 27 years, heat had slowly melted the 1/8" thick plastic tab to less than

1/16" of an inch until the relay tab actually fused to bracket attached to frame ground. Voila, short! I've identified the part at a Sears webpage. Hope to order it tomorrow, but if it's unavailable I'll fabricate small teflon insulation "dots" and glue them to the existing plastic.

Thank you all for the guidance and ideas, Mike

M> >

[J. Clarke]

Just a comment, and not relevant to your problem, but if you are in the US you might want to take a look at

If your saw is affected it gets you a new blade guard and table, for free.