I am a CET, and I am a fan of olosed lloop stepper/servo’s.
When using these drivers , the manual incorrectly says no resistors are needed when the driving signal is rail to rail 5 volts. But if you check the stats for a 6N137 which is used in these drivers for input opto-isolation you will find a max current limit of 15 milliamps. However that translates to something nearly 30 milliamps when driven by a signal stealer plugged into the 2209 socket. this will eventually blow the led in the 6N137 as it is nearly twice the max current rating.. It will fail, maybe 15 months, maybe 30 milliseconds.
Install a smalll R (170 to 190 ohms) in series with the - terminals of the step and dir terminals will fix that hopefully forever.
Hanpose was notified so maybe the instructions have been updated or the 6N137 has been replaced with something more robust, IDK.