Stepper motor driver problems - L297/298

[brentonw2004]

Hello. I recently built a bipolar driver using a L297/298 combo. I basically followed the datasheets given for the 297/298 and added some screw terminals and adjustments for control. I just finished assembling everything today, but I cannot get it to work. When powered on, the motor just vibrates and hums. I am using two separate computer power supplies to power the driver. One for the logic and one for the motor supply with the grounds tied together. I have the connection for SYNC left open, CLOCK going to a 250Hz 5V square wave, and CW/CCW grounded. I am certain that the motor is wired in the correct order. I have tried the driver with CONTROL enabled and disabled with very little change. I have not observed any smoke, excessively hot components, or anything else to suggest that the circuit is fried. I tested and made sure all the chips were getting power. I have attached a copy of my schematic that I made. Any advice would be greatly appreciated as to the validity of my schematic or suggestions for troubleshooting my issue. Thanks!

 

[ClydeCrashKop]

250Hz is way too fast. Use a 555 timer to trigger it at about 10 Hz until you get it working, then you can turn up the speed. Even manually single step it to start.

 

[SeanL]

also, what voltages are you measuring on the motor outputs and the supply input voltages.