19th February
written by Todd Harrison

This is Part 6.  It is the final installment because I did get the power supply working. You may want to first follow (part1), (part2), (part3), (part4) & (part5).

Somehow I or the crap designed circuit damaged one or more of the chips during part 1.

I started by testing my extra PWM chip (UC3843N) on a bread board. It was a new chip which was never used and it was testing fine until I turned the wrong knob and let out all the magic blue smoke. I took out the PWM chip that was in the control board since part 1 and it tested as bad. In fact Vcc was being shorted to ground. That explained a lot.

I ordered another PWM chips from Digi-Key and after installing it the controller and motor started working. I was having some speed regulation issues which I attributed to not having the heat sinks connected. At that time, which was the end of my video, I assumed the controller was functioning the best it could considering its poor design.

After delivering the motor and controller to HeatSync Labs one of the clever hackers there looked into the speed regulation issue which was not clearing as I thought it would once the heat sinks were mounted. He found another chip on the board that was bad, one of the op-amp chips. It was a chip I too had replaced over a year ago so something was killing the chips on the control board quite easily. This control board was such a pile of crap from day one.

It is working marvelously now so if you’re ever in Mesa Arizona swing by HeatSync Labs and try out their great little mini lathe. Maybe make yourself an aluminum chess piece or two.

Thanks for joining!


  1. [...] It can be a real drag to fix a circuit board which has stopped working as intended, especially if you don’t have any reference material for the product. That’s the position that [Todd Harrison] found himself in when the controller for his mini-lathe gave up the ghost. He undertook and hefty repair process and eventually mapped out and repaired the driver board. [...]

  2. 22/02/2012

    Nice work Todd! Glad you finally got that thing working after all this time.

  3. brian

    This was a fantastic series! I would love to see more of these sorts of very in-depth troubleshooting videos from you. To someone just starting out reparing electronics, this is pure gold!

  4. Graham

    A couple of tips from one who has repaired many power supplies.
    1 Always use an isolation transformer from the start.
    2 Put about a 100W light globe in series with the AC input. With no load this will have no effect when testing but any fault with the board should not blow any more bits up but will just light the globe up. The state of the globe will also show how much current is being drawn.

  5. Graham

    3 Consider using a light globe or two ( of the correct voltage) in the output as a dummy load whilst testing.

  6. 30/08/2012

    @Graham, O’so true. I got the light bulb tip from others as well. I have purchased the parts to make an in-line light globe switch box, just haven’t put it together. I should make a post on that with a demo video because it is such a great tip. Thanks.

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