The solution involves connecting the output of the opto-isolators to Schmitt-triggered buffers (such as the 74HC14 or 40106) as this will produce sharp transitions when the output of the opto-isolator crosses the voltage thresholds of the Schmitt trigger.

But there was an even bigger problem with the opto-isolators: They were not even isolating!

The role of an isolator is to electrically isolate two circuits from each other. However, the designers made the ground on the controller common to the ground on the parallel port by connecting the grounds on both sides of the isolator together. This means that the parallel port is still susceptible to noise spikes and large EMFs that can potentially be generated by the controller.

Fixing this issue is next to impossible, as all of the electronics are integrated onto a single PCB; therefore, the best solution is to just bypass the opto-isolators entirely or design a custom parallel port isolator that sits between the controller and PC.

Grounding and Noise





Sometimes, ICs have large ground and/or heat removal pads on their undersides that need to be connected. The TB6560 is no different as it has a very large heat dissipation pad on its backside but this heatsink pad should also be grounded as to prevent damage to the IC. However, none of the TB6560 Axis controllers ground this pad, and thus, when one of the TB6560 ICs fails, it causes the other TB6560 ICs to fail (if it is a multi-axis board). The solution is to take a piece of wire (preferably with a ring) and connect it to the screw or bolt that keeps the TB6560 in contact with the heatsink. The other end of this wire should be connected to a ground point on the main PCB. This prevents voltage spikes on the heatsink, which can transfer to other TB6560 ICs connected to the same heatsink.

The solution to this is to take a piece of wire (preferably with a ring) and connect it to the screw or bolt that keeps the TB6560 in contact with the heatsink. The other end of this wire should be connected to a ground point on the main PCB and this prevents voltage spikes being present on the heatsink, which can transfer to other TB6560 ICs connected to the same heatsink.