3 phase stepper driver problem

[vsystems]

Hi, we've got a cnc bed that's using two of these syntron sh-30806n stepper drivers, one of them went nuts one day and we're looking for a way to repair or replace it, however since none of us know how these operated even after extensive googling/searching etc. and we're unable to get in touch with the manufacturer to get replacements, I'm looking for some advice. The one axis works fine, but the second driver has a problem when it's moving slow, it just vibrates the motor and eventually it moves into "high speed" travel mode and it starts to move. Of course this prevents it from operating correctly at all since it's almost always in the slow travel mode while engraving.
Basically, is there any way to easily diagnose if there is a specific component on the driver that we can replace, or is it not worth the effort and I should look for a complete driver unit replacement? I'd really appreciate any ideas on what to do to fix this. Thanks in advance! If i didn't provide enough information, just let me know.
http://www.hollysys-electric.com/dow...r/30806-en.pdf