My Jet 1642 lathe is only developing about 500 RPM instead of the 1200 it should in low range. It also has significantly less torque, making it difficult to turn anything even with a light touch & sharp tools.

It has a 3 phase inverter, and I suspect one of the phase legs have failed.

Is it possible that the inverter is contaminated with fine dust? I turn a lot of tropical hardwoods and frequently sand to a very high grit and wonder if the silica common in them could somehow be interfering with the inverter circuitry. Since the lathe is long since out of warranty, I'm considering opening it up and blowing it out with compressed air to see if that helps and possibly cleaning the circuit board with alcohol.

Has anyone else experienced this, and if so, how were you able to resolve it?

Update: It's now three years later, the lathe is behaving completely normally and I've done nothing beyond cleaning it really well. I suspect it may have been water intrusion since the lathe sits right up against my garage door. I have put in a plywood panel to prevent direct spray, but that's really just a guess as to what the actual problem might have been.

  • No I haven't, but I do have a jet lathe and am interested to learn more about this. My only problem with mine is the eye that measures the speed never stays lined up, so I gave up resetting it and it always reads 0...
    – bowlturner
    Apr 1, 2015 at 1:10
  • Did it work fine until recently? Has anything else changed; for example, did you replace any parts or move it to a new circuit or a new shop?
    – rob
    Apr 16, 2015 at 6:27

2 Answers 2


You didn't say how much work your lathe has seen, but here's what the user manual has to say about the symptoms you mentioned:

Motor or spindle stalls or will not start

  • Excessive cut. Reduce cut depth.
  • Worn motor. Replace motor.
  • Broken belt. Replace belt.
  • Worn spindle bearings. Replace bearings.
  • Improper cooling on motor. Clean sawdust from motor fan.

Motor fails to develop full power.

  • Power line overloaded. Correct overload condition.
  • Undersize wires in supply system. Increase supply wire size.
  • Low voltage. Request voltage check from power company and correct low voltage condition.
  • Worn motor. Replace motor.

I suppose some of the above may also apply to the inverter--for example, as you suggested, maybe the inverter os overheating and needs to have the dust blown out.

In addition to the above, the belt could possibly slip and cause low torque and maybe low RPM if it's worn, dirty, and/or not tensioned (also if it's the wrong size belt or if it has stretched).

  • Nothing has changed, but you've given me an idea. I'm plugged into a line of wiring I ran myself (ex-USN electrician), which is only several feet from my breaker box. However, I'm also plugged into a power strip, and it might have gone bad even though it's a commercial version. It sits on the floor right next to my garage door, it could have gotten wet in a storm (not overly likely, but possible), there may be corrosion inside it. I'll check that over the weekend. Thanks for the response to give me other things to consider.
    – delliottg
    Apr 16, 2015 at 15:03

You can test the voltage on each leg of the inverter with a multi-meter to confirm your suspicious. Between any two phases you should get the equivalent of the square root of 3 multiplied by the voltage. So if your supply voltage is 120V, you should get ~208V between any two phases.

One layer of a printed circuit board is a solder mask (this is what gives the board its color), so dirt on the board itself should not short out the individual traces. Blowing dust off of it won't hurt, but I doubt it will resolve the problem. If something did short out, that component is likely damaged.

Assuming you do trace the issue to the inverter, I would start with a visual inspection of the board, look for burnt or bulging components. Smell the board too - if you get a strong smell of "burnt" and/or ozone, something is likely fried. Whether or not you can fix it is probably outside the scope of this site.

If the inverter is OK, check and test all of the electrical connections - maybe you'll get likely and something has just come loose.

Might also be worth reaching out to Jet to see if this is a common symptom of a particular problem they know about.

  • Steve, thanks for the comments. I was an electrician in the USN and I've got the tools to check the legs as you laid out. I also work for a company that lives & dies by their PC boards, so I also know what the magic smoke and it's effects smell & look like. This problem has happened once before and a phone call to Jet seemed to clear it up (I did absolutely nothing because of the phone call, so the lathe seemed to know I was talking to them and started to behave). I like the idea that something has shaken loose, that would be great to find. I'll update when I know more.
    – delliottg
    Apr 1, 2015 at 20:20
  • @delliottg It's been 10 months - do you have an update? Just wondering.
    – Ast Pace
    Feb 5, 2016 at 5:33

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