Shopsmith Forums

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judaspre1982 wrote:Not sure if that motor has thermal overload protection, but if so, you may want to check for continuity thru the overload switch. I have had these devices fail from time to time for no apparent reason.The ones I refer to are the bi-metal type that open when an over heat occurs in the windings.

Dave

There is a thermal overload switch on the main motor but the main motor works fine. I can't find an overload switch on the lift motor which is where the problem is.

A little more info.

In addition to the AC cable there is a signal? cable running from the main control panel to the same circuit board as the AC line. This signal cable has 4 wires that attach to the circuit board.

It appears that the circuit board may be 24VDC but the motor is not. When I attach a voltmeter to the motor on the wires that come from the circuit board and attach to the brushes, I get readings I don't understand. If I measure on the DC scale I get 100 VDC if I measure on the AC scale I get 240 VAC. The input to the board is 120 VAC.

The other thing I don't understand is why do I get any reading at all? All I did was to turn on the electronic panel without selecting any actions. It seems to me that I shouldn't get any reading at the motor UNLESS I instruct the saw to raise or lower.

tdubnik wrote:There is a thermal overload switch on the main motor but the main motor works fine. I can't find an overload switch on the lift motor which is where the problem is.

A little more info.

In addition to the AC cable there is a signal? cable running from the main control panel to the same circuit board as the AC line. This signal cable has 4 wires that attach to the circuit board.

It appears that the circuit board may be 24VDC but the motor is not. When I attach a voltmeter to the motor on the wires that come from the circuit board and attach to the brushes, I get readings I don't understand. If I measure on the DC scale I get 100 VDC if I measure on the AC scale I get 240 VAC. The input to the board is 120 VAC.

The other thing I don't understand is why do I get any reading at all? All I did was to turn on the electronic panel without selecting any actions. It seems to me that I shouldn't get any reading at the motor UNLESS I instruct the saw to raise or lower.

I cannot explain the AC voltages being present at the motor; what I would be looking for is a DC voltage to the stepper motor.

Do you measure DC anywhere on the circuit board and if you do, what potential.

Do you see a bridge rectifier on the board anywhere. The output from that bridge should be an "on demand" DC voltage.

:mad:I wish I could join you in the shop. I love to work on this sort of problem.

I understand from your description that the system uses a stepper motor. The way it functions is it knows the position at zero height, it then sends a series of pulses to the motor to obtain the required height. Each pulse represents one section of rotation of the motor, for example 1 deg. Unfortunately this means that using a voltmeter will not give any meaningful results as they are only accurate when measuring DC and AC at about 50/60 Hz. This is why you are getting strange results.
Sorry I cannot be more helpful in diagnosing the problem but I hope this will help you understand how a steeper motor functions.

Like I said, I wish I could be there in the shop to work on this. Keith, DC is DC and AC is AC. Either can be measured if using the right instrument.

I had another thought to go along with all else that has been discussed. This could also be a control problem. That is to say, the motors and power supplies could all be good while something else is causing the problem.

Questions in pix.
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I do not think this is a 'stepping' motor.

The 'strange' voltage reading will depend upon what type of meter you are using.

What is under the board on the opposite side(the side the control cable goes to)?.

I'll try to do some more analysis and get some better pictures tomorrow.

Stay tuned.

I took another look at things this morning and just raised some new questions.

When looking at the circuit board I don't see a rectifier that converts AC to DC. (second pic below)

The label on the motor itself indicates 120 VAC. The input to the circuit board is 120 VAC. Now the question is what voltage should run the motor and is it AC or DC? I tired to measure the voltage but you see the strange results I got in the previous post. I thought about hooking 120 VAC directly to the motor but am worried about burning up the circiut board or motor.

I do not believe this is a stepper motor. It appears that height is controlled by a sensor. I believe the main contorl panel sends a signal that turns on the motor and determines direction (up/down).

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The 4 black things with a stripe on one end are diodes and are connected as a a full wave bridge would. The + and minus outputs are the white wire and red wire respectively. The red thing connecting these points is either a small capacitor or a resistor(cannot see enough of it). Now the power input(120v ac) is unusual in that the neutral(white) only connects to the brown wire. It would be helpful to know what wires go to what on the motor.

The motor appears to be an universal motor(runs on either ac or dc) but the dc polarity will determine direction if field and rotor polarity rare reversed. Cannot tell much about control cable 'side' (wires in way).

Need to know both field winding connections and brush connections.

DO NOT CONNECT 120V AC TO ANYTHING ON THAT MOTOR! I do not think it is 'wired' for direct application(field/rotor not so connected).

More analysis and pics.

Here is a better picture of the circuit board with the wires and connections annotated. Notice that the brown wire is connected directly to the white of the AC input and then directly to the motor winding. This would indicate to me that the motor is running AC.

Another interesting thing is that the right half of the circuit board is seperate from the left half. You will notice that there is no bridge or components connecting the right and left halfs of the board. I believe that the right half of the board is a sensor circuit that sends the height information to the main panel. I'm not sure how it works unless the two little black boxes are some kind of proximity sensors as there is no physical connection from this side to the motor other than the mounting screws for the board itself.

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