More testing, and a video !

The 10,000uF 35v capacitor arrived yesterday, so I connected it across the power supply to the board, but the glitching was unfortunately still there. I also added a further 0.1uF capacitor as well but this was no better. The scope showed that the capacitor reduced the ripple, but the steppers still glitched.

With this scope connected to the power supply input I could monitor the waveform at different motor speeds. At very low speed (1KHz) there was ripple, which you would expect, but there was also a sort of saw tooth pattern which might be the stepper pulses appearing at the power supply. The stepper was glitching at these lower speeds.

As I increased the frequency up to about 6KHz the waveform started to smooth out and the saw tooth slowly disappeared. The stepper was then very smooth and did not glitch. Above 6KHz the waveform and the steppers continued to be smooth.

I've posted a private video on YouTube. Sorry it is low quality, my camera is quiet old. Also, YouTube has moved the sound well ahead of, and out of synch with, the picture. Don't know why.
www.youtube.com/watch?v=q8Ov7v74Kbo

I've sent all this info to Roy at DIYCNC to see if a replacement PSU is the next thing to try.

Other info, when I turn the steppers by hand, the blue power light comes on on the board (when it is switched off). They must be generating current as alternators. If I drive the steppers with my cordless drill then at quite low speed the drill stutters. If I repeat this but don't plug the motors into the board then the drill can spin them up to high speed very smoothly. Is this all normal behaviour?

Thanks
Barry