HighTekBikes
100 mW
Testing and Replacing Hall Sensors in a MAC Motor
When your motor runs rough, quits running or makes noise and runs hot, the first thing you should check is the hall sensors. It is 90% of all motor problems. Although you can test sensors with a voltmeter, Hightekbikes sells a handy tester for $39.95. Everyone with a sensored motor should have this in their tool kit.
How to test Sensors:
First, it is useful to think of the mysterious hall sensor simply as a NPN transistor. Instead of a base lead to turn it on, a magnetic field turns it on. The collector of an NPN floats when not connected so it is always pulled high with a resistor. It drives to ground and sinks current when on. So there are three leads +power, ground, and the collector output. Note that since the output floats, it will measure as an open circuit unless it is pulled up by a resistor. The controller has the required resistors internally, and supplies +5V to power the sensors. Therefore, it is easy to test the sensors with the controller connected and turned on. The only issue is probing the connections on the connector without shorting out the probes. This circuit is ground referenced so you always measure from ground (black wire on meter and connector) to the sensor output. To measure without the controller connected, you need to use a resistor to pullup the sensor lines, one at a time. The supply voltage, in this case +5V, is used. Simply connect the sensor lead to a 10K ohm resistor, then to the 5V lead on the connector. Any resistor from 2K to 100K will work fine (available at Radio Shack). You measure at the sensor lead to ground. While holding the probes, slowly turn the wheel, it should go from +5V to ground. A DD motor can rotate either direction, a geared motor has to be turned backwards. The sensor will operate up to 15V so you don't have to use 5V, you could use a little 9V battery or a 12V, whatever you have handy. If it is stuck high or low, or 2-3V, then you have a bad sensor. Obviously you have to check for broken wires which would measure 0V. If you can't determine if there is an open or a stuck low condition, simply measure from the sensor output to the +5V (or other supply voltage) which will read the supply voltage for a stuck low and zero for an open.
If you don't have a meter and are too cheap to buy one, you can use a 25 cent LED instead. You just need one more resistor, about 500-1000 ohms. Solder the resistor in series with the LED and use that instead of the meter. The difference is that you now go from +5V to the sensor output instead of ground. First, connect to ground and +5V (with resistor connected) to determine which is the plus and minus side of the LED. One way it will light up, the reverse will not. So now when the sensor turns on, it will supply ground to the LED, turning it on. Leave the pullup resistor mentioned above connected while testing.
Replacing sensors in MAC motors:
You don't have to replace the PCB, but you have to be handy at soldering. First, follow the colored wire for the bad sensor up to the PCB and locate the correct traces leading to the sensor. Carefully cut or chip away the epoxy above where the pins are soldered in. There maybe some of this glue under the PCB where the sensor is, if so this has to be cut loose so you can partially lift the PCB. Clip the leads close to the sensor so the legs are hanging down under the PCB. Unsolder the legs, pulling them out with the needle nose plyers. Use a solder sucker or solder braid to clear the pin holes. Next remove the old sensor. This can be a little tricky, so some patience is required. It's clued in so you have to force it out by tapping on it with a small screw driver or pointed tool. Don't worry about breaking it into pieces, just clear the side channels that the sensor case slides into. Be careful not to damage the layers of metal around where the sensor goes, or scrape the lamination off the coils. Put the new sensor in, it only fits correctly one way. While inserting it into the slot, first insert the three wires into the PCB. You have to bend the leads at a 45 deg angle and lift that section of the PCB while inserting the leads. Next glue the sensor in position with a drop of super glue. After that dries, solder the leads to the PCB and trim the leads. Test the sensor by running a magnet over it, then re-assemble the motor.
When your motor runs rough, quits running or makes noise and runs hot, the first thing you should check is the hall sensors. It is 90% of all motor problems. Although you can test sensors with a voltmeter, Hightekbikes sells a handy tester for $39.95. Everyone with a sensored motor should have this in their tool kit.
How to test Sensors:
First, it is useful to think of the mysterious hall sensor simply as a NPN transistor. Instead of a base lead to turn it on, a magnetic field turns it on. The collector of an NPN floats when not connected so it is always pulled high with a resistor. It drives to ground and sinks current when on. So there are three leads +power, ground, and the collector output. Note that since the output floats, it will measure as an open circuit unless it is pulled up by a resistor. The controller has the required resistors internally, and supplies +5V to power the sensors. Therefore, it is easy to test the sensors with the controller connected and turned on. The only issue is probing the connections on the connector without shorting out the probes. This circuit is ground referenced so you always measure from ground (black wire on meter and connector) to the sensor output. To measure without the controller connected, you need to use a resistor to pullup the sensor lines, one at a time. The supply voltage, in this case +5V, is used. Simply connect the sensor lead to a 10K ohm resistor, then to the 5V lead on the connector. Any resistor from 2K to 100K will work fine (available at Radio Shack). You measure at the sensor lead to ground. While holding the probes, slowly turn the wheel, it should go from +5V to ground. A DD motor can rotate either direction, a geared motor has to be turned backwards. The sensor will operate up to 15V so you don't have to use 5V, you could use a little 9V battery or a 12V, whatever you have handy. If it is stuck high or low, or 2-3V, then you have a bad sensor. Obviously you have to check for broken wires which would measure 0V. If you can't determine if there is an open or a stuck low condition, simply measure from the sensor output to the +5V (or other supply voltage) which will read the supply voltage for a stuck low and zero for an open.
If you don't have a meter and are too cheap to buy one, you can use a 25 cent LED instead. You just need one more resistor, about 500-1000 ohms. Solder the resistor in series with the LED and use that instead of the meter. The difference is that you now go from +5V to the sensor output instead of ground. First, connect to ground and +5V (with resistor connected) to determine which is the plus and minus side of the LED. One way it will light up, the reverse will not. So now when the sensor turns on, it will supply ground to the LED, turning it on. Leave the pullup resistor mentioned above connected while testing.
Replacing sensors in MAC motors:
You don't have to replace the PCB, but you have to be handy at soldering. First, follow the colored wire for the bad sensor up to the PCB and locate the correct traces leading to the sensor. Carefully cut or chip away the epoxy above where the pins are soldered in. There maybe some of this glue under the PCB where the sensor is, if so this has to be cut loose so you can partially lift the PCB. Clip the leads close to the sensor so the legs are hanging down under the PCB. Unsolder the legs, pulling them out with the needle nose plyers. Use a solder sucker or solder braid to clear the pin holes. Next remove the old sensor. This can be a little tricky, so some patience is required. It's clued in so you have to force it out by tapping on it with a small screw driver or pointed tool. Don't worry about breaking it into pieces, just clear the side channels that the sensor case slides into. Be careful not to damage the layers of metal around where the sensor goes, or scrape the lamination off the coils. Put the new sensor in, it only fits correctly one way. While inserting it into the slot, first insert the three wires into the PCB. You have to bend the leads at a 45 deg angle and lift that section of the PCB while inserting the leads. Next glue the sensor in position with a drop of super glue. After that dries, solder the leads to the PCB and trim the leads. Test the sensor by running a magnet over it, then re-assemble the motor.
