Hi...there is a 30amp cable running from the house meter to a consumer unit in the shed. This is fitted with a main RCD and separate trip switches for the lights, shed ring main, and separate supply to the plasma cutter. The rcd in the shed works as it should. I am going to fit an earth rod as well.

The power supply to the drives is separated... not daisy chained. Two drives have a 36volt input the other has a 27 volt. I have a separate 5 volt psu... this is daisy chained to the three drives. The last thing I did before the BOB blew was to fit 4700uf caps across the main (not 5v) supply of each driver...I'm not sure if this actually killed the BOB..

I bought a spare BOB which I have just tried (without the plasma cutter) and all the drives are fine so the drivers have not blown. Looking at the new 'broken' BOB ...there is a small hole in one of the two 74HC245 chips ...a 3 state octal transceiver. How this has blown so quickly is probably the answer to my problems!! As I said....whenever I use the machine without the plasma to try out my codes and make sure of my material limits I never have a problem...only when the plasma 'fires up' and then this is intermittent...sometimes it's OK...but not very often!

I had already ordered 3 new drives from China but they wont be here for a week or two....they are HY-DIV268N-5amp microstepping drives.....not sure if any better than the ones I already have though....they are supplied with a breakout board that has a jog control fitted.

I am tempted to order the ZAPP toroidal supply (which has a 5volt tapping) and get shut of my other three psu's and the large filter unit which isn't helping. I've already removed the electrolytic caps in case they were to blame!!

I'm losing faith in ever getting this to work...I even suspect my RTech P40F plasma cutter could be the problem but just cannot afford another model at this moment.