In the past few weeks I've been working on a new CNC instructable, but I was having trouble getting my motor drivers to cooperate. At first I couldn't seem to get them all to even start up. I decided to try out these Texas Instruments DRV8825-based Stepper Motor Driver Module designed as a drop-in replacement of my existing drivers:
I was getting better results but still missing some steps so I checked the 3.3V from my modified phone charger. It was showing the expected voltage on the multimeter, but when I looked with my $20 single-channel oscilloscope, I saw frequent peaks above 9V.
I added an electrolytic capacitor I found and smoothed out the peaks to around 3.6V. That's it, right? Wrong! It took a few more trial runs and a night to sleep on it to realize I also had a mechanical binding issue on the x-axis. After removing 2 screws, it's working great again.