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Powermatic 3520B repair help

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Our local high school has a 3520B that won't run. My understanding is that the problem began during a demonstration late last school year. The then shop teacher explored the problem and couldn't find any loose connections or obvious explanations. I don't know if he tested the on/off switch or rheostat/potentiometer but doing so is within his skill set. When I heard about the problem from the new shop teacher, I assumed it was one of the 'something's loose in the headstock' problems that Powermatics get, but my exploration didn't find any of the usual suspects. The prior shop teacher thought the VFD was the culprit. The rpm counter on the front lights up, so the unit is getting power.

Our local electrical engineer/Powermatic owner could easily identify the problem, but he unexpectedly passed away during the summer. Help.

We would appreciate you thoughts on causes and how to determine what the answer is.

Dean
 

Dave Landers

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Could be the VFD, but I'd start with the simple stuff. Here's some things I would look at to at least check the controls.

Check the on/off switch with a meter or short across it and see if the lathe spins (I've had problems with mine getting dust in the microswitch actuator thingy and refusing to turn on). The controls are run at low voltage, 10V, so you're not going to shock yourself.

Turning the knob should change the frequency on the VFD's display, even with the on/off switch off.

When operating normally, the VFD display should have a Run light that comes on when the on/off switch is on, and Fwd and Rev lights that indicate the direction. But the switch on the control panel doesn't flip those Fwd/Rev lights until the on/off is switched on and the motor runs.
 
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Could be the VFD, but I'd start with the simple stuff. Here's some things I would look at to at least check the controls.

Check the on/off switch with a meter or short across it and see if the lathe spins (I've had problems with mine getting dust in the microswitch actuator thingy and refusing to turn on). The controls are run at low voltage, 10V, so you're not going to shock yourself.

Turning the knob should change the frequency on the VFD's display, even with the on/off switch off.

When operating normally, the VFD display should have a Run light that comes on when the on/off switch is on, and Fwd and Rev lights that indicate the direction. But the switch on the control panel doesn't flip those Fwd/Rev lights until the on/off is switched on and the motor runs.
Curious... Dave, what was the fix for the dusty microswitch? Any way to prevent that from reoccurring?
Thanks
Al
 
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Does this lathe have the remote emergency cut-off switch (the one on a pendant)? We have 8 PM3520B's and occasionally have problems with the remote switch.
 
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For the Delta S1 inverter, there are three inputs required for the inverter to operate. A Run command, A Direction command and A Speed reference command. There are 3 LED’s on the left side of the display for the RUN, FWD and REV command. With the E-stop button out, Run Position, you should have the RUN LED. Push the button in, E-Stop position and the RUN LED should go out.

With the E-Stop in RUN position and the RUN LED displayed, change the position of the FWD and REV switch and the corresponding direction LED’s should change status. There is an alfa numeric display on the control face that can be programmed to indicate several things. I believe the default is F for frequency input to the Inverter. If you have the display starting with an “F”, slowly rotate the speed control potentiometer from minimum “0” display to maximum about “135” and back to “0”. The display numbers should increment and decrement smoothly and without any noticeable skips. Yes, the Inverter is programmed to overdrive the motor to about 135 Hz. The inverter will not operate w/o the “F” speed reference input even if the e-stop is working, in the RUN position and you have a FWD or REV signal.

If any of the above inputs are missing or the speed reference is unstable, those inputs need to be corrected. I suggest you run this test first to try to pinpoint the problem before you poke around in the wiring and/or blow out switches or the potentiometer with compressed air. It should take less than 30 seconds to perform once you have done it.

Check the tightness of all wire terminal connections. A good thing to do every 2-3 years anyway. Be sure the machine is disconnected from the power source.
 
Last edited:
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If you have another motor you could wire a length of 4-conductor S/O cord from the VFD and the other motor and test to see if the motor runs and the VFD controls the speed of the motor. Having another VFD you can use it to test to your motor to verify it is good.
 

Dave Landers

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Curious... Dave, what was the fix for the dusty microswitch? Any way to prevent that from reoccurring?
Thanks
Al
Seems that the plastic slider thing between the button and the actual switch gets stuck. I blow the switch out with air, then lube the slider with graphite. It used to happen fairly regularly but now it's pretty rare - so maybe the graphite is doing its job.

I also have my controls remote - in an outdoor conduit box, which does help keep the switch cleaner.
 
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OK, I was in the shop briefly yesterday and had time to look at the VFD readings. On the working model, the VFD numbers and indicators were exactly as Joe suggested above. However, the VFD on the down machine showed only 8888 (maybe 88.88). There is no indicator for FWD or REV on this Delta S1 VFD, but there are 3 little dots of light on the side of the display whose function is unclear and which didn't change during the maneuvers. Spinning the speed dial/potentiometer did not affect the display at all. Nor did any combination with the on/off button.

New or modified thoughts? I didn't have time or tools to check the switch or wiring yesterday.
 
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The 8888 code shows the following replies from one of the tech sites.
This is for a different series of Delta VFD, did not see this code listed in the S series VFD manual.
A call or email to Delta customer service should answer your question.

What should I do when the LED of a VFD-M series drive displays a 8888 or 9999 error message?​

The fault may occur for the following reasons:

.If the drive is still operating normally but the LED displays an error message, the LED is malfunctioning. Please replace the LED control board.

.If the drive has stopped operating, please reapply the power again. If the drive is still not operating, then it is the drive that is malfunctioning. Please send your VFD-M series for repair or replace it with a new drive.

Here is a link to the S series Delta VFD manual
 
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Thanks Mike. That's very helpful. I'm away from home meeting my newest grandson, so I can't dig into the innards at this time and having such great assistance is wonderful.
 
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Dean,

The VFD could be having an issue with an input value.
You might check your potentiometer resistance, jumper connections and switch contacts on the E-Stop button and forward & reverse contacts.
If one of these is outside the normal values the VFD could hang up in the program.
De-energize the Lathe/VFD and use a multimeter in the resistance mode and measure the contacts for continuity and measure how many ohms
of resistance the potentiometer provides at the low end and high end. A bad set of switch contacts will hang up the VFD program.
A loose terminal connection for a jumper wire or a loose terminal connection on a power conductor or ground/neutral conductor can also cause
a VFD to hang up the program. A poor connection on a jumper wire can hang up the VFD program.
Re-energize the lathe/VFD switch your multimeter to A/C voltage mode and measure your input voltage going to the lathe/VFD.
Use the multimeter in the A/C voltage mode and measure your output voltage going to the motor.
If you have an output voltage, your motor or motor feeder conductors could be bad.
If you don't have an output voltage there is most likely a problem with the VFD.
 
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