PM 3520b VFD acting up

[Don A. Davis]

My 8 year old lathe is used almost daily. Normal start-up is to hit the dedicated wall outlet switch, wait for the "click" of the VFD, pull the on-off button and go to work. Recently it's become a long (20 seconds) wait or the "click" doesn't come at all. I try the reset button, the run button, the wall switch, etc. Eventually I get success. Through all this there is power from the outlet because the light is on in the rpm indicator. PM tech support suggested a loose wire in the VFD. I checked and all seem secure. Recently I noted that a sharp tap on the VFD box with my fingers arouses it to produce what I want. Any theories?

[Malcolm McLeod]

I have no experience with your lathe, but lots with similar industrial controls. The results of your 'sharp tap' make me agree with PM tech support - - it certainly sounds like a loose connection. But it may not be a wire.

You indicated you checked the wiring. Did you check just the field connections to VFD (power supply and motor wiring)? Or, have you checked the I/O wiring as well (wires to start/stop/speed control switches)? A loose connection to these could also cause similar issues.

If you've checked all the wires entering and leaving the VFD, it's then time to look at any onboard wiring. Typical VFD has several sub-sections that may either be wired one to the other, or plug-mounted on a backplane (motherboard). Check for any loose plugs or boards that me be improperly seated. (Be safe, disconnect from power first.)

Last visually inspect for any damage or arcing on the component boards themselves. A surface mount component's solder or one of the foil surface conductors on a circuit board may be cracked. Your only sign of a problem may be some discoloration from any arcing that may occur across the crack. (Your tap could be just enough to close the crack, start current flow, cause the component to heat, expand, and keep the crack closed while in operation.)

If it is a board level failure, it may be an Easter egg hunt to find it, and simplest fix may to replace the VFD in whole or part. PM tech support can hopefully be more assistance if it comes to that, as they may be able to help isolate the issue to one component or board - - and not have to replace the entire VFD.

Edit - If a crack exists in the low voltage (5Vdc?) control circuitry, it may literally be microscopic in size, and impossible to see. Or, it could be in the solder joint under a surface mount component, and also impossible to see. Trouble-shooting is often a matter of remove-and-replace until the problem goes away. It is aggravating to replace a $100 board, due to a solder joint in a $0.002 resistor, but in today's world it cost more to trouble-shoot down to the component level than it does to simply replace the board (or entire VFD).

[terry mccammon]

I am with Malcolm but will also offer that you might simply need to be very careful and really blow out any and all dust from controls (speed pot, on/off switch, etc.) as well as the enclosure and so forth.

[Malcolm McLeod]

How many turner's have VFDs on their lathe?

Anyone else have reliability issues?

Anybody (or any manufacturers) use shock mounts on their VFD/speed control?

Anybody remote mount their VFD (off the lathe)?

I was curious, so looked at PM site and noted that their VFD is simply screw mounted to back of the headstock. VFD is subject to high vibration (unless all you're turning is small stuff, i.e. pens), and this 'high-G' environment is typically advertised as being very hard on circuit boards and such.

(if you contemplate moving or shock mounting the VFD, make sure the grounding is still adequate!)

[Don A. Davis]

Thank you Malcolm and Terry. Some of that was over my head but I will open up the box and take a closer look. If all else fails I will keep finger tapping (until that fails!).

[Steve Schlumpf]

Don - I agree that if you can tap the unit and get it to working - then you have a loose connection somewhere. Thing is, that loose connection could be at the front panel switch. With all the vibrations a lathe experiences, look for where a wire is free to vibrate/move. The on/off and speed control wires are not supported and could be loose at the switch. After you remove power, they are easy to access through the front panel.

[bobby stout]

I have a 1642 2hp that I had to do the same thing, took VFD off check all wires and still did the same thing. the lathe was only 3 months old then it final got to the place that it would not work at all. Jet was outstanding sent me another one and it has been a year now and it is working fine. Bad news it your if it has not died maybe it is only a lose connection.

[Mike Golka]

I had a similar issue with my Oneway. It turned out to be a broken or poorly soldered connection on one of the capacitors. I found it by removing the cover and tapping the case. that caused a small spark at the bad connect. This was easily fixed and has been running for a couple of years now.

[Dick Strauss]

I had a similar issue with my Oneway. It turned out to be a broken or poorly soldered connection on one of the capacitors. I found it by removing the cover and tapping the case. that caused a small spark at the bad connect. This was easily fixed and has been running for a couple of years now.

I think a friend's 3520 lathe had the same issue. He could tap it and move the wire bundles to make it work again until it finally quit. I re-soldered the caps to the board and the VFD seems to be running fine since.

[Josh Bowman]

This would be my plan of attack. The controls, E stop, fwd/rev, speed control are all about 24 volt controls and very low current. The E stops on the PM often give problems. Per Steve S. instructions, I quit using the E stop years ago in leu of a remote switch. I have found that if any dust gets into that remote switch, the lathe will not start. Having said that I'd first using air, blow out all the switches on the control panel. Then while you have the panel off, check the connections, the E stop button uses screws to hold the wires, I think I remember the other connections are spade type. Then on the back of the VFD, locate the terminal block near the botton outside of the box where the control wires are landed. These are small terminal screws, tighten each of them. OF COURSE YOU ARE GOING TO DO ALL THIS WITH THE POWER OFF AND ALLOW THE LATHE TO SIT 5 TO 10 MINUTES BEFORE STARTING. Then if you still have problems, go deeper as mentioned above. Resoldering may be the solution.

[Malcolm McLeod]

I realize that 5 similar experiences/responses don't exactly amount to a smoking gun, but if you are all doing large turnings that start in less-than-perfect balance, and all have VFD solder issues .... could it be a trend???

Shock mounts on VFD? Remote mount the VFD?

If VFD is subject to high vibration, the 'high-G' environment is typically advertised as being very hard on circuit boards and such. (sorry, to be repetitive)

[Bill Boehme]

I have no experience with your lathe, but lots with similar industrial controls. The results of your 'sharp tap' make me agree with PM tech support - - it certainly sounds like a loose connection. But it may not be a wire...

I agree with all that you say as a logical process to isolate the problem ... if it can be isolated. I can attest to board level problems being exceedingly difficult to isolate and is an expert level only type of repair.

One recommendation that I would like to add when checking the 5v logic connections (start, stop, fwd, rev) and speed control potentiometer on the terminal strip is that checking these needs to go beyond just checking that the screws are tight. The connectors on these wires are normally crimped over the insulation and designed to pierce through to the conductor. Sometimes the pierced-through-the-insulation type connections are a bit tenuous (nice word for flaky) and can become intermittent. The one "iffy" part of this presumed likely failure mode is that once things start working, they continue to work until powered off if I correctly understand what happens in this situation.

Anyway, I would suggest using an insulated tool and wiggling each of these logic input wires when the VFD isn't behaving to see if an intermittent connection is the source of the problem. It would be really fortunate if this leads to solving the problem, but I wouldn't hold my breath just yet.

[david privett]

I do not know if your unit has one but there might be a micro relay that is the issue. Tapping would make these activate where there was a open circuit via high resistance contact. It might be a good idea to verify if the board has one. If you have the knowledge or a friend that can read a schematic. Then maybe you can isolate your tapping to whittle down the area on the board where the problem is.

[Dick Strauss]

I should have added in my original note that the 3520 lathe I turn on has had problems with the main start/stop mushroom switch (replaced by PM after it would no longer blow out) and remote switch (which has been taken apart several times for cleaning when blowing out didn't work). I would definitely check these switches first.

I don't know if vibration causes the problems with the internal VFD connections or temperature cycling. Temperature cycling can be a big killer of electronics especially with the VFDs braking functions every time you stop.

[Don A. Davis]

Thanks everyone for the really good input. My plan this week is to get the area behind the lathe clean enough I can get back there to do some of the investigating that has been suggested.