Scott,

I received your support ticket.  Thanks for the links.
I know double optoisolation can be very tricky, and we have had problems with this in the past.  I can assure you this has nothing to do with the problem you are experiencing now.  Depending on the board, some can optoisolated at 100khz and others at 1Mhz.

I presume this is the board you bought back in 2008.  Are you just setting this up now, or was it working ok and then it started having problems?

The problem you are describing makes me think that the board is underpowered.  Possible causes for this are:
-   Problems with the power supply.
-   External short draining power from the system.
-   Damaged chip on the board, which can create an internal short, leaving other chips underpowered.

I suggest you take a look at this guide for trouble shooting this with your board: 

Please let me know how it goes.

Arturo Duncan
http://cnc4pc.com

Scott,

I had this same type of problem with a New Hermes engraver that I converted to run from Mach3,  The opto were too slow. 
It manifested the problem by climbing in the z, x & y axis all in one direction. 
I was doing some text engraving and the letters ran at an up hill angle, getting lighter and lighter, and closer and closer spacing.
Since the driver board was all TTL circuits I simply jumpered out the opto isolators.

Right now it seems like that is where the problem lies for me as well.  Need to do some more testing to be sure.
Thanks
Scott