About this time last year I purchased a Harbor Freight mini lathe that I documented here. Having the need to cut some circles out of copper lately, I once again became frustrated with the DC speed controller’s unwillingness to reset after it’s overload protection circuitry has been engaged.
This generation of the lathe (purchased in 2012) uses a DC drive motor and a Chinese made speed controller with the part number FC350BJ/110V. Astonishingly, I’ve actually found some technical information on it, and there even appears to be a few individuals out there that repair them. Fortunately mine was not faulty.
I came to believe the board was the culprit in part because I made the cardinal mistake in troubleshooting – I made an assumption. I assumed that the switches and controls on a brand new machine would be functional and that there was no reason to test them. Shame on me. Thankfully after several failed attempts to locate other owners experiencing this problem, I stumbled upon this forum post from 2009. Lo and behold, a quick check of the safety switch on the back of the speed potentiometer revealed the problem – the switch never closes, the signal from which is used to reset the overload protection system.
After wiping the egg off my face, I disconnected the one lead to the back of the pot, and added my own normally open pushbutton in it’s place across terminals 3 and 5 of the control board. If you had any idea how many hours I’ve wasted fruitlessly wiggling on controls and tapping the control board with screwdriver handles, you’d laugh yourself to tears instantly.
Once this problem is resolved this lathe immediately begins to resemble a tool more than a toy.