My Mach3 driver has been working ...... until now, when for no reason its has started to go all over the place according to the driver test. There have been no external changes to the breakout board or motor driver controls and no changes to the computer configuration or software. Now the motors will not drive properly of course.

Is there any info on what may have caused this failure?

Could it be a hardware failure in the PC (Laptop)? On occasions the Mach3 test screen will show the CPU speed lower than it should be. However there seems to be no correlation between this and the horrible waveform that is occuring even when the CPU speed indicates at the corret value.

Here's an update ...... I thought the driver may have become corrupted somehow and reloaded the Pulser.ico file. First time I ran the driver terst it was OK the second time and subsequent times it was not.

My floppy drive is an external device via a USB port. and moving the laptop to and from the workshop the drive was disconnected. By chance I put the drive back in after the a failed test and behold the test was OK. I found that if during the test I unplugeed and plugged the disc drive the timings went haywire with the drive unplugged and OK when plugged back in.

Why the problem came to light was because I had not plugged the floppy disc drive in as I did not need the tap files that were on it. I did not consider for a moment that such an action was the cause of the mill not working.

Now Mach3 automatically looks at my floppy drive when I go to load a G code file and I suppose that as the drive was not there even though I was not loading any G code file Mach 3 expected the drive to be there and was continually poliing to find the drive and mucking up the timing ..... is this the likely cause? any experts likey to know please.

I am not familiar with the problem at hand but your CPU speed you mention could just be a normal laptop function. Many laptops including mine are configured in the bios to lower the cpu speed when not needed to save on battery power. Like I mentioned my own does this as well and shows no effect on Mach.
 B. Ender