I purchased the Univelop / CNCgeeker 4/5 axis TB6560 driver boards (see photo) a few weeks ago and got them working on my new homebuilt CNC router but found that it was missing steps (see photo) and the errors were repeatable and were not speed dependent. After changing nearly every setting in Mach3 and Windows XP, I narrowed it down to the Univelop / CNCgeeker TB6560 driver board.
When a direction change was sent from Mach3 to the parallel port, it was correct but a delay mismatch in the optocouplers on the driver board was causing the step pulse to arrive at the TB6560 IC sooner than the direction pulse. So the motors were turning one step in the wrong way after each direction change!
I have attached a photo showing the step pulse happening before the direction pulse. This is measured at the step and direction pins of the TB6560 IC.
I was able to fix this by swapping a resistor and shorting another. I published the details of this fix on my web site at cockrum.net
A perfect example of the kinds of problems people run into with these cheap Chinese drivers. Congratulations on having the tools, knowledge and time to solve this one.