I'm trying to diagnose a non functioning treadmill with my limited experience. I've traced out part of the circuit that I believe is the culprit. But there's one area (at least for this discussion!) that I don't understand how it works. It's the circled mosfet transistor in the attached circuit diagram.
How does the transistor turn on/off when the gate is connected to ground through a resistor? I believe what should happen when the motor is called for is that the coil supplies 120VAC to the SCR Diode module which in turn supplies a VDC to the motor when G1 & G2 are energized. G1 & G2 are energized when 4.9VDC on pin 1 of the optoiosolator gets through it, which happens when the gate of the transistor turns on. That then in turn supplies the 55VDC from pin 4 of the isolator to pin 6 and turns on G1 and G2 which turns on the SCR diode module, giving power to the motor. Currently, there is 4.9VDC at pin 1 and 4.1VDC at pin 2 of the isolator and that never changes regardless of the call for the motor. As a point of interest, if I ground pin 2 through a 10k resistor when the motor is called for, the motor works.....but only for a second until my arc-fault circuit breaker kicks off! I haven't wanted to try it on another regular circuit breaker for fear that it's not the arc(which I can not see) that is causing it to kick off but high current!
I've replaced the SCR diode module (at a cost of $50!) and the isolator to no avail. Maybe my problem is the transistor, but I would like to understand how it works.
Thanks for any help you can give me.
Doug
How does the transistor turn on/off when the gate is connected to ground through a resistor? I believe what should happen when the motor is called for is that the coil supplies 120VAC to the SCR Diode module which in turn supplies a VDC to the motor when G1 & G2 are energized. G1 & G2 are energized when 4.9VDC on pin 1 of the optoiosolator gets through it, which happens when the gate of the transistor turns on. That then in turn supplies the 55VDC from pin 4 of the isolator to pin 6 and turns on G1 and G2 which turns on the SCR diode module, giving power to the motor. Currently, there is 4.9VDC at pin 1 and 4.1VDC at pin 2 of the isolator and that never changes regardless of the call for the motor. As a point of interest, if I ground pin 2 through a 10k resistor when the motor is called for, the motor works.....but only for a second until my arc-fault circuit breaker kicks off! I haven't wanted to try it on another regular circuit breaker for fear that it's not the arc(which I can not see) that is causing it to kick off but high current!
I've replaced the SCR diode module (at a cost of $50!) and the isolator to no avail. Maybe my problem is the transistor, but I would like to understand how it works.
Thanks for any help you can give me.
Doug
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