Hi all, I also have one of these Chinese Wonders (It's a Wonder that it works!) with the Chinglish Manual and misspelled PCB designates. For my efforts I decided to fit Home/Limits to the X, Y, & Z planes which went quite smoothly until I inspected the I/O Board.

So I set about to bring this into line with half decent components. I upgraded both the 5v and 15v Regulators. Changed the polarity protection diodes for 3A shottkies which have a much lower forward voltage drop than the !N4007’s.
I also changed all the electrolytic’s for 108° low ESR, replacing the 407µF with a 1,000µF The PCB has all the locations needed to fit 5 Opti-Couples and the pull-up resistor network needed for the home/limit switches.
I thought I was doing ever so great and about to do a bit of ‘Yankee Back Patting’ as I connected everything up and switched on..
This time the Spindle Motor didn’t Rev it’s nuts of as usual and the System Fan did not work.... Yep, you guessed right I miss-connected the Fan and Spindle Motor Controller. No big deal as I didn’t see any ‘Smoke Escape’ 1 However, putting 15V directly across the Anode and Cathode of the Motor Controller Opti-couple ensured its demise.
Whilst I was investigating the possibilities of any further damage I rung out to continuity the return line from the connector to the Parallel Port Pin 1.
The Drawing Les, (Pointy) has painstakingly provided is a great help apart from the Motor Line from Pin 1 is connected to the 5v Line via one of the 330R pull-ups, and the second connection to ground. This is incorrect. Pin 1 from the parallel port connects directly to the Opti-Couple on the Motor Controller Sub Board. Be very careful when tackling any problems with the Motor Controller Board It is connected directly across the Mains with enough current to blow your hat off !!

Scoping the Signal, DC Lines, and I/O lines shows that my efforts in upgrading the components has paid off with reduced electrical noise.

1As the Mach3 Manual says, ’Contrary to belief Electronic Components work with Smoke. There is no documented evidence that and device has ever worked once the smoke has escaped’