Hi!
I'm trying to repair an old treadmill that is not working. It's an Aeorobics Inc Pacemaster 870X. After a period of not using the treadmill (summer time), it stopped working. Currently, when the start time and start speed are inputted and then the start button is pressed, there is a short delay and then a message shows on the display saying there's a dead sensor and the tread does not move (I'm assuming the problem is not the sensor since there is no movement of the tread to sense). I have troubleshooted it extensively and have replaced a few parts ($50 worth!) to no avail. Rather than go into all the details of that, can anyone help me understand how the circuit works that powers the motor? I've drawn the relative part of the circuit and have attached it.
When the user inputs the speed and distance and presses start, the relay closes and provides power to the Crydom L512F SCR diode. When power is supplied to the gates, a DC voltage is applied to the motor. The gate signal seemingly is a 120VAC signal that goes through an optical isolator. The isolator is turned on when a VN 2222 transitor is turned on with a signal from the microprocessor.
What I don't understand is:
1. What voltages at the Crydom gates would be expected? DC or AC. And is that appropriate? I don't think I've traced the PC board incorrectly. The specs for the Crydom are here: http://www.crydom.com/en/Products/Catalog/l_3.pdf
2. How does the speed of the motor vary? Does the microprocessor turn the transistor on and off at different frequencies such that the effective voltage to the motor therefore can vary?
I have found that if I ground pin # 2 of the opto isolator, the motor and tread works, but quickly shuts off and a different message is displayed that would indicate that the speed of the motor is not correct (not surprising). So I'm afraid that the signal from the microprocessor is not correct, but I don't have an O scope to look at it. But could the microprocessor be bad since many of the other functions work, eg the display, the incline angle, the diagnostic messages, etc.
Any suggestions to further troublshoot? I've replaced the Crydom module and the opto isolator.
Thanks in advance for any help!
EDIT: Minor change to schematic
I'm trying to repair an old treadmill that is not working. It's an Aeorobics Inc Pacemaster 870X. After a period of not using the treadmill (summer time), it stopped working. Currently, when the start time and start speed are inputted and then the start button is pressed, there is a short delay and then a message shows on the display saying there's a dead sensor and the tread does not move (I'm assuming the problem is not the sensor since there is no movement of the tread to sense). I have troubleshooted it extensively and have replaced a few parts ($50 worth!) to no avail. Rather than go into all the details of that, can anyone help me understand how the circuit works that powers the motor? I've drawn the relative part of the circuit and have attached it.
When the user inputs the speed and distance and presses start, the relay closes and provides power to the Crydom L512F SCR diode. When power is supplied to the gates, a DC voltage is applied to the motor. The gate signal seemingly is a 120VAC signal that goes through an optical isolator. The isolator is turned on when a VN 2222 transitor is turned on with a signal from the microprocessor.
What I don't understand is:
1. What voltages at the Crydom gates would be expected? DC or AC. And is that appropriate? I don't think I've traced the PC board incorrectly. The specs for the Crydom are here: http://www.crydom.com/en/Products/Catalog/l_3.pdf
2. How does the speed of the motor vary? Does the microprocessor turn the transistor on and off at different frequencies such that the effective voltage to the motor therefore can vary?
I have found that if I ground pin # 2 of the opto isolator, the motor and tread works, but quickly shuts off and a different message is displayed that would indicate that the speed of the motor is not correct (not surprising). So I'm afraid that the signal from the microprocessor is not correct, but I don't have an O scope to look at it. But could the microprocessor be bad since many of the other functions work, eg the display, the incline angle, the diagnostic messages, etc.
Any suggestions to further troublshoot? I've replaced the Crydom module and the opto isolator.
Thanks in advance for any help!
EDIT: Minor change to schematic
Attachments
Last edited: