GEN7 stepper problem

Hi

I bought a ready made GEN7 1.3.1 board and having finally got the teacup firmware loaded (no changes other than the baud rate and board type)

I can drive 3 out of 4 of the stepper motor channels. One channel (Y) steps back and forth and doesnt rotate smoothly as the others do.

I have swapped steppers and the motor runs fine on another axis.

I have swapped out the small stepper motor driver boards and this runs other channels fine. So it must be something on the motherbaord I assume.

Any things to check? Broken tracks, solder bridges? Anything else to try?

Thanks!

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Any things to check? Broken tracks, solder bridges?

Yes, yes and yes. I'd guess on the motor side of the Pololu. Power the thing off, pull the Pololu out and measure the coil resistances of the connected motor at the Pololu header. Also check for shorts between both coils. You can use another channel for reference. I've already seen a lot of cold solder joints at the motor headers.

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Anything else to try?

You can also check the signal side of the Pololu. The DIR pin should receive a stable 5V or 0V, depending on commanded direction. The STEP pin should show a low voltage while moving, 0V while at stillstand. "Low voltage" means a constant voltage, depending on the commanded speed. The higher the speed, the higher the average voltage. An oscilloscope would show rectangular 5V signals of constant width, closer together at higher speeds. A cheap multimeter is usually suffiecient, though. The ENABLE pin is 5V for off, 0V for enabled. Should also be stable.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Thanks. will give it a go. hopefully something simple like a solder bridge. Fingers crossed

Hi

I checked for bridges and nothing obvious. Checked the resistance of the stepper with the pololu board taken out and is about 6.8 ohms (slightly less than the motor by itself but I guess there is some reisitnace from the board side).
To check the voltages on the pins, can you point me to a pin assignment diagram. On the Reprap page for the Gen 7 it shows the board but not the pin assignments.

Thanks once again!

The pin assignments are printed on the back of your Pololu/StepStick and also here (EN = Enable):



BTW., make also sure the microstepping jumpers are in a valid state. In doubt, pull them all out.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY