This treadmill problem is driving me nuts - Please help

[Frank747]

I am posting this in the hope that you learned gentlemen out there may be able to help me with my treadmill problem.
My treadmill is an Infiniti model MA100, with a DC motor (180 V, 7.5 A). The circuit diagram and photographs of the Motor Control Board are attached. While I was running on it at 8 km/hr it suddenly stopped. I turned the power off and after a few minutes turned the power on again and press the start switch. The motor ran normally at very low speed but when speed on the console was incrteased past 2km/hr or with a load on, the treadmill stopped and displayed an E1 error, which is related to speed sensing. I then did the following:

1. Replaced the speed sensor. This made no difference
2. Checked the motor operation using a 12 V battery. Motor ran as normal with no sign of mechanical damage. Measured the static resistance of the armature winding at 2.5 Ohms.
3. Checked the Motor Control Board (MCB) for any obvious damage such as blown capacitors, resistors, burnt tracks, etc. No damage could be seen. Then disconnected and tested every semiconductor (transistors, diodes, optocouplers) on the MCB as well as every capacitor. Found transistors Q6 & Q7 to be faulty. These are unknown types, so I took a punt and replaced them with a BC558B and a 2N3710 respectively.

After the above checks and repairs, the current situation is as follows:

1. 
   With the motor disconnected from MCB
   
   (a) Switch treadmill on
   - Console display seems to be normal
   - Voltage measured across M- & M+ is 0 V
   - Voltage at collector of Q1 =11V
   - LED 5 (speed sensor led) is OFF
   (b) Press Start
   - Console display seems to be normal
   - Voltage measured across M- & M+ is about 7 V
   - Voltage at collector of Q1 = 320 V
   - LED 5 (speed sensor led) is OFF
   - After 6 seconds console displays E1 error (as expected since there is no input from speed sensor)

1. 
   With the motor connected to MCB
   
   (a) Switch treadmill on
   - Console display seems to be normal
   - Voltage measured across M- & M+ is 0 V
   - Voltage at collector of Q1 =11V
   - LED 5 (speed sensor led) is OFF
   (b) Press Start
   - Motor does not spin
   - Console display seems to be normal
   - Voltage measured across M- & M+ is about 7 V
   - Voltage at collector of Q1 = 320 V
   - LED 5 (speed sensor led) is OFF
   - After 6 seconds console displays E1 error (as expected since there is no input from speed sensor)
   
   With the motor disconnected from MCB and run separately on a 12V battery
   
   (a) Switch treadmill on and press Start
   - Motor spins as normal
   - Console display seems to be normal and timing starts
   - Voltage measured across M- & M+ is 7 V
   - Voltage at collector of Q1 =320 V
   - LED 5 (speed sensor led) is OFF
   - MCB is receiving speed sensor signal and so treadmill stays on. No errors shown
   
   With treadmill ON and Start pressed
   
   - measured 320 V b/w collector & emitter of Q1
   - measured +12 V & -12 V at output of voltage regulators IC1 & IC2 respectively
   - measured 15 V across capacitor EC6 (output of rectifier bridge 2W06)

The only component I haven't tested (apart from each resistor on MCB) is the Astar -101 baby board because I don't know what to test for (I have no circuit diagram for it). Could this board be the culprit? I hope not because I don't know where I would be able to get one from.

I have spent many hours on this treadmill problem and I don't know what else I can do. So any help would be greatly appreciated, please.

 

[Tha fios agaibh]

Components can test fine but fail under a load.
I would isolate the power supply and see how much load it can handle (within its output rating) without the voltage dipping.

Perhaps D2 or the bridge rectifier is failing under a heavy load?

 

[Frank747]

Thank you Tha. As shown in the circuit diagram there are 3 power supplies. 1) +12V & - 12V regulated power supply; 2) high voltage supply to the motor; 3) unregulated 15 V power supply via rectifier bridge 2W06. Since you mention diode D2, I guess you are referring to 1) above. I have tested the outputs of the regulated power supply with the treadmill turned on and the start button activated, and they have the correct voltage. The motor was not running so I guess this test was not under load? I will try what you suggested, that is to isolate that power supply from the rest of the circuit and test it again. My gut feeling is that the base of transistor Q1 is not getting a signal and therefore it's not turning on thus not delivering any current to the motor. What do you think?

 

[Tha fios agaibh]

Print is a bit hard to read but a few thoughts.

Strange that Motor + is ground. It first made me think Q1 was for voltage regulation.
Its base is fed from Q5 which needs Positive at its emitter (print marked -12) and it base voltage would to be less than that to fwd bias it.

Have you checked the opto isolators?

 

[Frank747]

I apologize for the poor quality of the diagram. I downloaded it from a similar post and then made some amendments based on my board layout.
Just to be clear, M+ is connected to the board ground or common point and not mains ground.
You are right about the emitter of Q5. I have checked the board tracks and amended the circuit diagram accordingly (please see attachment).
As you suggested, I have also measured the output voltages of the regulated power supply under simulated load conditions using a resistor, with the following results:

IC1 (+12V regulator)
- no resistor across pin 3 and earth, V=11.86
- 100 Ohms resistor across pin 3 and earth, V=11.84
- 27 Ohms resistor across pin 3 and earth, V=10.64 (dropping to 9.96 V after pressing Start on treadmill)

IC2 (-12V regulator)
- no resistor across pin 3 and earth, V=-11.92
- 100 Ohms resistor across pin 3 and earth, V=-11.90
- 27 Ohms resistor across pin 3 and earth, V=-11.38 (dropping to -10.70 V after pressing Start on treadmill)

Do you think the voltage regulators are faulty? Any thoughts on that?

 

[Tha fios agaibh]

I don't know how much current is required but adding a 100Ω resistor will only load it 120ma. A lower resistance would be better but probably unfeasible unless you have high wattage resistors or a load bank or smaller motor to hook up.


Likely a problem with the power supply somewhere.

I don't think it's a regulator but I've seen diode and bridges test ok but fail under load.

I would try it with the motor connected and follow along both positive and Negative sides of 12v rails and try and see where along the path that the voltage collapses.

Measure voltage with respect to ground.

Good luck