Shopsmith Forums

raweber wrote:To answer a few other questions - the power cord is the original that came with my Dad's Shopsmith that he's used for the last 30 years. It's in really good shape.

If a new power switch doesn't do the trick, my next stop will be the take the motor out and take it apart as much as I can to clean it out. There is a lot of fine dust visible inside it.

Thanks for all the help. I'll report back what happens.

The start switch parts move very little on the Emerson motor. A very small saw dust particle could prevent it from making. Unfortgunately the actual contacts are not visible(they are covered by what I think is intended to be a dust shield)(?).

A little gentle banging on the motor housing may release it.


That said, the switch is now the prime culprit. Make sure you did not short out the motor side(or just plain miswire it).

A pix of the switch(as wired after rebuild will help).

If you have an ohmmeter, this might be very easy to isolate.

Unplug the Mark 5/V power cable from the wall.

Turn the Mark 5/V power switch to OFF.

Measure resistance from each of the two AC power pins. You should measure infinite resistance (an open).

Now Measure the resistance between the ground pin and either of the two AC power pins. You should measure infinite resistance (an open).

Now measure the resistance between the ground pin and the other of the two AC power pins. You should measure infinite resistance (an open).

If you measured anything other than infinite resistance, you have either a bad switch or an AC power wire shorted to ground.

By measuring the resistance between the two power pins (on the end of the Mark5/V power cord) while switching the Mark 5/V power switch on and off, you should see the resistance change from infinite to near 0 ohms. If there is no obvious change in resistance, chances are you have a bad switch (always on or always off). A bad switch will MOST LIKELY NOT cause the breaker to trip.

My 12' cord measures about 3 ohms.

To see the effect of an extension cord, plug the Mark 5/V into an extension cord and then make these same measures (last step from above) at the end of the extension cord. The measured increase in resistance is the reason why it is not advisable to use an extension cord with the Mark 5/V.

raweber wrote:To answer a few other questions - the power cord is the original that came with my Dad's Shopsmith that he's used for the last 30 years. It's in really good shape.

If a new power switch doesn't do the trick, my next stop will be the take the motor out and take it apart as much as I can to clean it out. There is a lot of fine dust visible inside it.

Thanks for all the help. I'll report back what happens.

When I replaced the switch that failed on my 520 I had this issue, it turned out when I replaced the switch I created a short and the breaker was doing exactly what it was designed to do. All I had to do was correct the connections to the switch.

As recommend use an ohm meter to check the wiring and switch first, before plugging it in.

I found this thread that might help you (assuming you have the toggle switch as opposed to the "Red Key" switch):

https://forum.shopsmith.com/viewtopic.php?t=711

Particularly this post from charlese:

charlese wrote:Looking at the back of the switch - The two white wires go to the left corners of the switch. The white from the motor goes to the top left and the white from the line goes to the lower left.

Also from the back - The two black wires go to the right side of the switch. The black one from the motor goes to the upper right and the one from the line goes to the lower right.

I suggest you draw a picture of a rectangle with labels showing these wires attaching to the corners. You'll have it next time.

Best regards,

I think the wires from my motor were white & green but it was an A.O. Smith motor. The line wires were white and black as charlese describes. If your motor wires are different colors, that should still give you some guidance - the white wire should be the same at least.

It's got to be the wiring hooked up to the switch... that would be my guess... An easy test is to bypass the switch altogether and hook power to the motor directly... I suspect it will turn just fine...

[quote="JPG40504"]The start switch parts move very little on the Emerson motor. A very small saw dust particle could prevent it from making. Unfortgunately the actual contacts are not visible(they are covered by what I think is intended to be a dust shield)(?).

A little gentle banging on the motor housing may release it. QUOTE]

Normally, when a motor hums, it is the centrifugal start switch points being open. I have never found a bad capacitor in any Shopsmith motor. I have not found this open point problem on the Emerson motor with the dust shield covering the switch points. I assume the dust shield helps keep the switch points clean. I have not figured out how to remove and reinstall this dust shield without damage yet or had a need to file the contact points.

I find humming in the GE and AO Smith motors are caused by the centrifugal switch points being open. Many time, a rubber hammer contact on the motor pan (drill press position) will clear the points to where the motor operates again. I always file the points on either of these motors when I disassemble them. A thin nail file will work to file the switch points.

raweber wrote:All right - I pulled the drive belt - still no go. For the record the motor is an Emerson C55DDR-2015. I can't believe it's anything too exotic since it's what came in my Dad's stock Shopsmith thirty years ago.

Now the twist - it's started blowing the breaker whether it's turned on or not, which makes me suspect the switch. My car's in the shop right now but when I get it back later today I may make a run down to the hardware store and see if I can get a replacement switch.

With this symptom - I do not see how the centrifugal switch could be the cause. When the centrifugal switch is the factor, the contacts are either open (sawdust accumulation preventing closure of the contacts) or the contacts are badly pitted (creating high resistance contacts).

With the switch turned off, if the breaker is tripped the problem is most likely in the power cord or POSSIBLY the switch.

I am reminded of a switch controlling a fireplace flue. After half a dozen experts were unable to figure out the reason my gas fireplace would not operate properly one electrician isolated the problem to the switch mentioned. I appeared to be nearly impossible to get to. The guy finally managed to remove the bottom of the switch box and began to remove the switch. We both noted a fairly large speck of sawdust fall to the hearth. The guy looked at me and said do you suppose that was the cause? The fireplace had been in that house for fifteen years and seldom worked. It worked perfectly every time asked to fire up after that. I asked the guy if blowing a little bit of air in the switch housing might have dislodged the dust. He thought a minute and grinned that he now had a great argument to have an air compressor on his truck. Come to think of it I have read the suggestion of blowing air out of the motor and pan housing when cleaning our Mark V's. Fjimp

dusty wrote:With this symptom - I do not see how the centrifugal switch could be the cause. When the centrifugal switch is the factor, the contacts are either open (sawdust accumulation preventing closure of the contacts) or the contacts are badly pitted (creating high resistance contacts).

With the switch turned off, if the breaker is tripped the problem is most likely in the power cord or POSSIBLY the switch.

With the input that the breaker now trips even with the switch off, the attention must shift from the motor to the power switch!

I 'speculate' the switch was mis-wired during refurbing.

I'm anxiously waiting to hear what the culprit turns out to be... Paul Harvey moment... we have to wait to hear the "Rest of the Story"...