Repair Craftsman electronic radial arm saw?

keith1445 · Post by **keith1445** » Mon Jun 06, 2011 2:45 pm

I have attached the image showing the motor wiring. If you can detail the codes on all the components we might be able to diagnose the other circuit

dusty · Post by **dusty** » Mon Jun 06, 2011 3:04 pm

tdubnik wrote: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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The two little black cubical devices are capacitors (part of the dc supply). The little brownish cylindrical device looks to me to be a resistor that is connected across the bridge rectifier. There appears to be a part number written on it that may cross (google it).

There are NONE of the typical signs of damage (over heat, etc) to the printed circuit board or the components. One wire (in the photos) appear to be discolored but that may be the photp image and not the part.

What is at the other end of the 4 control wires (red, black, yellow and green).

tdubnik · Post by **tdubnik** » Mon Jun 06, 2011 3:12 pm

dusty wrote:The two little black cubical devices are capacitors (part of the dc supply). The little brownish cylindrical device looks to me to be a resistor that is connected across the bridge rectifier. There appears to be a part number written on it that may cross (google it).

There are NONE of the typical signs of damage (over heat, etc) to the printed circuit board or the components. One wire (in the photos) appear to be discolored but that may be the photp image and not the part.

What is at the other end of the 4 control wires (red, black, yellow and green).

Dusty,

I don't believe there is anything on the power supply half of the circuit board that converts AC to DC.

Notice that the left and right halfs of the board are not connected by any bridges or components. I believe they are two completely different circuits.

The 4 control wires along with some others feed the microprocessor. That's why I believe they are only sensors.

The power has to be controlled from the main panel. The AC wire that connects to the circuit board also originates at the main panel.

dusty · Post by **dusty** » Mon Jun 06, 2011 3:28 pm

tdubnik wrote:Dusty,

I don't believe there is anything on the power supply half of the circuit board that converts AC to DC.

Notice that the left and right halfs of the board are not connected by any bridges or components. I believe they are two completely different circuits.

The 4 control wires along with some others feed the microprocessor. That's why I believe they are only sensors.

The power has to be controlled from the main panel. The AC wire that connects to the circuit board also originates at the main panel.

In post #19 and again in post #20 you can see four black cylindrical devices standing on end with a wire looping back down to the circuit board. There is a silver band on each of those devices. Notice that on two of them the band is near the board and on the other two the band is at the other end. Those four devices form a full wave bridge rectifier (converts ac to a pulsating dc voltage).

The control circuit is an integral part of this power supply.

tdubnik · Post by **tdubnik** » Mon Jun 06, 2011 4:00 pm

dusty wrote:In post #19 and again in post #20 you can see four black cylindrical devices standing on end with a wire looping back down to the circuit board. There is a silver band on each of those devices. Notice that on two of them the band is near the board and on the other two the band is at the other end. Those four devices form a full wave bridge rectifier (converts ac to a pulsating dc voltage).

The control circuit is an integral part of this power supply.

Thanks Dusty,

I'll yield to you on this one because I am not electronics savvy.

JPG · Post by **JPG** » Mon Jun 06, 2011 11:36 pm

Have you checked the metallic object in the middle that a black wire goes to(from????) that is covered in an insulating film? Possible fuse/overload device.

I agree re right side, but what are they 'sensing' on the rotating parts? Those 'cubes' have three terminals.

Unclear is what controls on/off/direction. Are you sure the '120v' is 'ac'?

JPG · Post by **JPG** » Mon Jun 06, 2011 11:58 pm

Keith, you were close, but you got two diodes reversed.

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The pink? thing across the armature is probably a capacitor, but may be a resistor.

Missing is the metallic object mentioned before.?????

keith1445 · Post by **keith1445** » Tue Jun 07, 2011 5:29 am

Sorry about that, more haste less speed. Can I suggest we understand how the operation of the height control is preformed on the equipment. I think this might help in the diagnosis.
To operate the height adjustment do you dial in a require height and press the go button or do you press a button to activate the motor and watch the dial until it reaches the required dimension.
If either is the case it is highly likely that a measurement scale is incorporated in the pillar providing feedback, this is like an electronic vernier calliper.
It would be beneficial to understand this operation, we could then decide the most likely area of control mechanism is at fault. As previously suggested the fault could either be the control circuit or the power to the motor circuit.
From the comments concerning voltages at the motor this might suggest that the controller thinks it needs to adjust the height as is trying to do so. Indicating again that the motor is at fault.
Can the mechanics of the height adjustment be operated manually, if they can that would rule out any mechanical problem.
I think as JPG says the unidentified object could well be a thermal switch stopping power getting the windings.

dusty · Post by **dusty** » Tue Jun 07, 2011 5:39 am

JPG40504 wrote:Keith, you were close, but you got two diodes reversed.

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The pink? thing across the armature is probably a capacitor, but may be a resistor.

Missing is the metallic object mentioned before.?????

Your corrected drawing depicts a full wave bridge OK - BUT - Are you sure that is what we are dealing with.

I assumed a bridge rectifier to start but that is not what I see now that I study the pictures more. The corrected drawing does not depict the circuit.

tdubnik · Post by **tdubnik** » Tue Jun 07, 2011 7:44 am

The metallic object could very well be a thermal overload but it appears to be intact.

The circular object on top of the motor shaft is magnetic as you can see from the screw I tested it with.

I believe the height is determined by counting motor revolutions. I think the right hand circuit does this. The two little black boxes are positioned close to the circular magnet when the board is properly attached. I see no evidence of a vernier scale inside the column. We need to also remember that the sensor wires are attached to the circuit board on the motor and the only wires I find on the column are the ones for the miter settings.

There are two ways to adjust the height on this saw. The main panel has a jog button with an up and down position. If you press the top on this button the saw raises, pressing the bottom lowers it.

The other way is to set a height from a reference point. Let's say you zero out the blade at table height and want to make a cut 1/2" above the table. First you would press the elevation ref set button to set the diaplay to 0. Next you would press the elevation button and use the keypad to enter .5. Lastly you would press the act button and the saw should respond.

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