Treadmill motor speed controller

Thread Starter

wings515

Joined Aug 7, 2015
14
I have an MC2100SD1-12 controller. I built a PWM using an NE556. I can vary the PW between 15 msec and 40 msec at a PRF of 50 msec. I am using this to drive a wood lathe. I placed a magnet on the drive pulley and connected the RPM sensor to the two terminal block marked HD7. When I first turn it ON it will run for about one minute and maintain speed. I have also used the sensor from the tilt motor to drive a tachometer so I can see the actual speed. After this first minute the motor will start to slow down and finally stop, The LED on the board is steady. Once in a while the LED will flash and the motor will try and turn. Measuring the voltage across the motor terminals confirms 0 volts when it is stopped.
I also measured the output of the line bridge and it was 108 volts. This seems low, I did measure the diodes in the bridge with a DVM in the diode mode but bridges can be misleading with this method.
Looking at the reverse engineered schematic, the zener D8 shows a 1N474. Mine is a 1N4744 and it measures 15 volts which is per spec.
One thing that is puzzling, the DC motor voltage referenced to bridge common is in the area of 150 volts on both sides of the motor when stopped.
I do have an HP1740 scope but I am reluctant to connect the ground of the scope to the common on the bridge output since this circuit is floating.+
Any ideas on the next step in T/S would be helpful.
Best regards,
wings515
 

Thread Starter

wings515

Joined Aug 7, 2015
14
Thanks for the reply. I did add the feedback sensor to the HD7 connector with the same results. I kinda thought an isolation transformer would be required.
Now all I have to do is find where I put that transformer. I know I have it somewhere.

Thanks
Dan
 

Thread Starter

wings515

Joined Aug 7, 2015
14
Found my isolation transformer and before I connected my scope to Common on the board I measured the AC voltage between Common and the scope ground with the transformer installed. It was 67.1 VAC. I did not want to proceed since this seems high to connect these two together. Also measured the AC output of the bridge, 53 VAC, I am tending to think the bridge is bad.
Thoughts?
 

Thread Starter

wings515

Joined Aug 7, 2015
14
Just thought, I put the isolation transformer on the scope, should I have put it on the controller board since the bridge is connected to the line voltage?
 

MaxHeadRoom

Joined Jul 18, 2013
19,449
I usually connect the equipment to the transformer.
If the circuit is anything like the pdf reverse engineered ver. the bridge is just for the DC supply, there is no SCR bridge on this one.
If so the bridge should show the AC in rectified.
It is an un-smoothed bridge so it will be less than 120v.
Max.
 

Thread Starter

wings515

Joined Aug 7, 2015
14
Bit the bullet and connected the floating common to my scope ground using an isolation transformer on the device. NO SMOKE! Started T/S and determined the SCR was not turning ON. Using the reverse engineered schematic of the MC2100 I grounded pin 2 of U4 the TD3052 which would fully turn ON the internal LED. This did not cause the motor to run full up. Probing pin 6 of U4 showed voltages in the area of 150 VDC with some ripple. Removing the power I checked the diode voltages again on the SCR and they seem OK but then I measured the resistance on all leads. Even in the circuit the Gate to Cathode resistance was 65 ohms in both directions. Back to the bench and I removed the SCR, again it measured 65 ohms in both directions out of the circuit. I placed an order at Digikey for 2 of them. They are less than $3 each. While out of the circuit I am going to check the TD3052 again to see that it is also not failed.
 
Top