PM3520C won't run

[Bill Schulz]

My Powermatic 3520C is about 1.5 years old and heavily used. Today (and previously on occasion) it would not reverse direction. Usually just flipping the reverse switch back and forth a few times overcame this. However it will not start at all now. Lights are normal except no green ON light. I've blown out the switch box and the VFD with compressed air to no avail. Also unplugged numerous times. I'm out of ideas and with Thanksgiving I'm sure Powermatic is out of pocket. I have projects needing finishing. Any suggestions will be appreciated. Thanks in advance.

[Bill Bukovec]

Do you have an ohmeter to check that the switch is closing?

[Bill Schulz]

Yes, I do have a meter and will dig in further on Friday. Hopefully not BLACK Friday for me. I hate messing around in that switch as there's 220 in there and I'm not a sparky. :-) Thank you for the suggestion and Happy Thanksgiving.

[John K Jordan]

Yes, I do have a meter and will dig in further on Friday. Hopefully not BLACK Friday for me. I hate messing around in that switch as there's 220 in there and I'm not a sparky. :-) Thank you for the suggestion and Happy Thanksgiving.

If the C model is like the B and “A” the switch is low dc voltage, 10v for the earlier models. But you don’t need it powered on to test. Unplug the lathe and test the continuity of the switch with the ohm or continuity setting on the meter. It should be obvious if the switch is bad, likely, based on what you said about flipping the switch to make it work on the past. Might also verify the connection back to the VFD.

Doc Green has a multi-part article about the control circuitry and switches for an earlier model, perhaps the new one is similar.
https://www.docgreenwoodturner.com/pmcontrol1.html

If you are not comfortable with the testing and belong to a local turning club I’d bet there is someone who would be glad to look at it.

JKJ

[Bill Schulz]

Thanks John. I used the Doc Green article for help replaceing the VFD on my previous Jet 1642 with good success. I remember being surprised that the digital display had 220v. Maybe my memory is worse than I thought. 79 years does strange things. :-) Happy Thanksgiving.

[Richard Coers]

Best chance is the switch itself is full of dust. That's where you need the air pressure, inside the switch body. You don't need to be testing a live box. Unplug the lathe and use the Ohm section of the meter that measures resistance across a connection by sending in a low level DC current from the battery in the meter. If the meter doesn't change with the switch in either position, the contacts are not touching. As the saying goes, "you just have to find where the current ain't!"

[John K Jordan]

Thanks John. I used the Doc Green article for help replaceing the VFD on my previous Jet 1642 with good success. I remember being surprised that the digital display had 220v. Maybe my memory is worse than I thought. 79 years does strange things. :-) Happy Thanksgiving.

Yes, the digital speed display has AC voltage as well as the motor, of course. All the control circuitry is low voltage. The 1642 is almost identical to the 3520a/b in wiring and function but with 5v instead of 10v.

[Bill Schulz]

I've opened the switch box and blown out everything reachable. That switch is a modular sealed deal with 6 connections. 2 NO (normally open), 2 NC (normally closed), and the remaining 2 (?). For some reason I think it may be what I've read to be a "magnet switch". That seems to me to need power applied to function but then again I don't understand the concept.

I'll try Powermatic tomorrow and I also have a friend who is an EE and understands this stuff. I also have another friend with the same lathe and he had a similar problem. PM sent him a new switch box for the fix.

[John K Jordan]

I've opened the switch box and blown out everything reachable. That switch is a modular sealed deal with 6 connections. 2 NO (normally open), 2 NC (normally closed), and the remaining 2 (?). For some reason I think it may be what I've read to be a "magnet switch". That seems to me to need power applied to function but then again I don't understand the concept.

I'll try Powermatic tomorrow and I also have a friend who is an EE and understands this stuff. I also have another friend with the same lathe and he had a similar problem. PM sent him a new switch box for the fix.

All 6 terminals are connected? Is it a toggle switch? Can the wires be removed from terminals on the back of the switch or do you have 6 wires coming out of a sealed (potted) switch?

A DPDT tobble switch has 6 terminals. The 3520a/b use a SPDT toggle switch with three terminals.
A SPDT magnet reed switch has three terminals, NO, NC, and Common. They typically change state when a permanent magnet is moved close to the reed. No external power is needed.
I have no experience with a DPDT magnet switch. I didn't know they existed. Of course, there's the possibility the switch is something else completely.

If it was mine I'd trace out the control wiring, make a diagram, and consult the VFD manual to understand the connections. (Most manuals are available online if one didn't come with the machine.)

I did a search and found several instances of people having odd problems with the forward/reverse on the 3520C. In one thread on another forum the gentleman solved his ongoing problem this way:
"I called Powermatic, described the problem to the tech who said they were shipping me a new switch, and told me how to install it. The switch arrived 2 days later, and it only took about 20 minutes to install it. Problem fixed."

JKJ

[Bill Schulz]

John, thank you so much for the research and information.

All 6 terminals are connected? Yes Is it a toggle switch? No Can the wires be removed from terminals on the back of the switch Yes or do you have 6 wires coming out of a sealed (potted) switch? No

My switch has 3 pairs of terminals ( does that equal 6 terminals?) and clearly marked NO, NC, and probably Common. I now understand how a magnetic switch works without power.

I've attached a pic of front and back of the unit. DPDT and NOT maghetic?

I do have a manual for the VFD and I do believe there is a schematic in there as well. And I have taken the cover off once just to see the fan setup so I know how to get inside of it.

[John K Jordan]

I'm definitely not familiar with that type of switch.

The terminals are nothing like the typical DPDT switch and don't make sense to me with the + and - pair in the center. (Does it actually need power to work?) I've never touched or even seen one of these lathes other than in pictures. The manual operation of that type of switch not clear from the picture - just curious, does it work like a rocker switch or is it a "soft" momentary contact switch that you push up or down and it returns to center?

It will be interesting to see what PM says when you contact them about the switch. If they say they'll send out a new switch you might ask them how much they usually charge for a replacement. If you do have to replace the switch I'd be very interested to see good photos of all markings so I could try to look it up.

It looks like PM has moved away from the type of control circuitry in the 3520A and B. I wondered what advantage the major changes from the B model until I found this article:
http://carlford.info/blog/2018/03/my..._verses_3520b/
Carl's description of the movable control box and the digital indexing system explains much. Having that function and all the controls in the movable box with only low voltage would require a major design change.

I downloaded the Delta series E manual and took a quick look at the control wiring and programming. They indicate 24v digital and 10v analog control voltages (for the speed control) so it should be safe to work on when powered up. It would be nice to see a circuit diagram of the control system but to understand this one may require knowing how the multi-function inputs 3-6 are programmed. (The manual shows 28 different program settings for these inputs!) With the earlier Delta S1 VFDs it was simple to examine and change the programming since the display and keypad was built in. It looks like for the Series E you have to connect Delta's optional digital keypad to even examine the programming. If it doesn't come with the keypad that may be a step backwards for those who like to understand and work on our own machines. When the VFD on one of my Jet 1642 lathes died I bought an inexpensive off-the-shelf VFD and programmed it to make the lathe. 3520C users might be stuck with getting a pre-programmed replacement from PM if the VFD dies some day ($$$).

It would be fun to get some hands-on time with one these lathes and figure out and diagram the control circuit.

JKJ

[Bill Schulz]

it's a "soft" momentary contact switch that you push in on the green to start, in on the red to stop. The only sound is a soft click from the VFD on start. I've never like that switch from day one but I was used to running the Jet1642 for 6 years. But that pull/push switch failed once for me also. I too replaced the VFD on my Jet with a Delta off the shelf model (~$350). I documented the process here.
https://drive.google.com/drive/folders/1rdJIBIUnBhXQOe_ERcftEjZLFQDUxEHt?usp=sharing
In fact I bought the keypad for the PM VFD as I wanted to change the fan parameter to always run when the lathe was running but found that it was locked to factory setting which is temp controlled. Once it turns on it runs for 20 minutes after the lathe is stopped. Annoying. I could actually read the Multi-function settings using the keypad. I also bought the keypad to document the factory settings in case it died someday so I could replace with an off the shelf unit and just reprogram if necessary. So far, I haven't done that. :-(
I'm attaching another pic that show a p/n on that switch but no joy in trying to look it up.

My EE friend is just itching to start digging into this thing. I'm just wanting to get a couple of projects finished before Christmas. :-)

[John K Jordan]

…it's a "soft" momentary contact switch that you push in on the green to start, in on the red to stop. The only sound is a soft click from the VFD on start. I've never like that switch from day one but I was used to running the Jet1642 for 6 years.

I’m actually wondering if the black forward/reverse switch is a spring loaded momentary contact, if when you push in one direction to reverse the lathe does it return to the center. If I can’t find the switch i’ll ask my electronics wizard friend Joe who so far has been able to find anything. He might even be familiar with that type of switch. I’d love to get my hands on a dead one and do an autopsy.

In fact I bought the keypad for the PM VFD as I wanted to change the fan parameter to always run when the lathe was running but found that it was locked to factory setting which is temp controlled.

Did PM lock all the parameters by passcode to keep people from messing with them? They did that on the earlier 3520s and 1642s. Hmmm, if they did I wonder if they used the same code. The earlier unlock code was widely reported on turning forums - I have it recorded somewhere.

But that pull/push switch failed once for me also. …

My EE friend is just itching to start digging into this thing. I'm just wanting to get a couple of projects finished before Christmas. :-)

The push-pull switch on one of my jet 1642s failed as well. I took it apart and found it clogged with fine sawdust. After a good cleaning and reassembly (with a little dielectric grease for good measure), I sealed the switch from dust and it’s worked since, 15 years so far. (fixing failed switches is a bit of hobby for me, over the years I’ve cut open and repaired dozens for myself and friends. Handy if the nearest replacement is a week away!)

Too bad you don’t live close - I could loan a spare jet 1642 to work on the Christmas projects in the event of an extended delay. I keep the 3520B and 1642 set up in the shop (handy for teaching) and a spare 1642 in my storage building “just in case”.)

[Kevin Jenness]

3520C users might be stuck with getting a pre-programmed replacement from PM if the VFD dies some day ($$$)
JKJ

I hate that. This proprietary electronic stuff is a pet peeve of mine. A shop near here is selling their functional NC Kolle panel saw and I am pretty sure the main reason is that replacement controls are unavailable as the mfr is defunct.

To the OP, good luck in sorting it out. I am thankful to all the folks like John K. who share their experience so generously here.

[Bill Schulz]

The black forward/reverse switch is a slider, not spring loaded.

PM did lock all the parameters by passcode to keep people from messing with them I think. I too had the passcode for the Jet, I think it came from Doc Green. However I never messed with the VFD for the 7 years I had it before the VFD failed, then it was too late to copy the parameters but Doc Green also had those so I could set up the new VFD.

The good news is I plugged the 3520C back into power last night and it's working as expected again. Go figure. Of course PM is closed until Monday so no joy there but I don't care until it fails again.

Next week my EE friend is coming over and we'll try to trace the wiring logic and diagram it to maybe help understand how the thing works, or don't. I'll keep you posted on status.