View Full Version : Intermittent X drive motor

05-22-2010, 02:24 PM
You guys are going to love this one. I have a feeling i will be in for a long troubleshoot, but wanted to check and see if I could generate a list of test.

As I said, this is a Intermittent X drive motor. Sometimes on power up and re-zero it sets up fine. Other times I can tell the gantry lags. If I cycle power on the controller I can get the motor back. When I have been able to check with a voltmeter I am getting the 68 or so drive voltage at the connector. I have not checked the signal voltage because I don't know what the value should be. I have a 4G Botrod controller on a PRT96. The motors are Vexta.

Let the analysis begin!!!!

Thanks guys....


05-22-2010, 02:53 PM
I don't think the motor will be "sometimes broke"

Wiring would be the first check (wiggle test) , then a gecko maybe.

The motors could be swapped with the Y one at a time.

Geckos could be swapped out as well.

When you swap a part and the problem moves,,, thats it.


05-22-2010, 02:56 PM
Since you have already verified that you have the proper operating voltage (68VDC), the next thing that I would do is to check all connections. Use a voltmeter and wiggle the wires as you check for continuity.

Next, check signal voltage. If you have G203v stepper drivers (Red case), you should have 0VDC between COMMON and STEP when the motor is idle. You will have about 5VDC when the step signal is active, but you'll probably need an oscilloscope to see the pulses. If you have the G202 stepper drivers (Black base), you should have 5VDC between COMMON and STEP when the motor is idle and 0VDC when the step signal is active.

Check the temperature of the Stepper controllers. They can get hot, but should not be too hot to hold your finger on. If they're too hot, they can enter thermal shutdown mode which normally requires you to cycle the power to reset. Hot stepper drivers can be kept cool enough by using a large heat sink. On my test bench, I mount the four stepper drivers onto a strip of 3-1/2 inch high by 20-inch long by 1/2-inch thick aluminum. They stay at room temperature.

If everything still looks okay, then swap two of the stepper drivers. (Turn off the power first.) If the problem moves to a different axis, then it's probably time to get a new stepper driver.

05-22-2010, 10:27 PM
Mike -

When you mention red or black case your are talking about the drivers in the controller, correct? One thing that can to mind that I was wondering as to how affective this would be. I an thinking about takeing a small lamp or even an LED if it is not bi-polar and hooking it up to the signal ine for each motor. Then I would have a visual as to if it was working or not. I probably need to do some experimenting to see if it draws to much power that it would affect the operation of the motor.

Any thought????

05-22-2010, 11:04 PM
Yes, the Red or Black is the color of the Gecko Stepper Driver.

The problem with used an LED is the current that it takes to light it up, which is about 10mA. Because an LED drops about 1 volt, a 330 ohm or 390 ohm resistor in series with the LED will limit the current to a safe value; however, the G202 sinks 15mA per signal line and the G203v requires a 2.5mA SOURCE per signal line. Depending on the chip that is used to feed the step and direction signals to the Gecko stepper drives, the LED circuit might overload the chip.

You might be able to find a tester or probe at Radio Shack for a reasonable price. I bought mine years ago, but since it is connected to +5V and Ground, the probe draws less than one TTL load, so it is a quick and easy way to test slow moving signals without getting out the oscilloscope. Most probes have a latch or pulse stretcher that keeps the built-in LED on long enough to see fast moving signals.