# (PROBLEM SOLVED) PM940 CNC VFD spindle question



## rodjava (Jun 29, 2020)

I fired up my PM940 cnc today and the VFD would not turn on. I notice that when I turn on the spindle on the Mach3 control panel, the KA1 "relay?" in the electronics cabinet turns on and off but this does not turn on the VFD.  I reset all the breakers that are lined up on the left hand side of the cabinet which did not affect the VFD.  Am I missing something that I should be trying?

Any help would be appreciated.
Rod in San Francisco


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## B2 (Aug 5, 2020)

Hi Rod,  

Not for sure if I can help.  Or, since your post is a month old, have you already solved your PM940CNC problem?  If you have solved it I a curious as to what the problem was.  

So,  I have the same machine and can supply you with a scanned copy of the Users manual if you do not have it.  It has some very limited circuit diagrams in it.  You may also want to download the Delta VFD manual. It is hard to see if you have the same Delta VFD that my machine has in it the model Nos. are on the side of the VFD.   (However, since VFDs are just programable computers controlling power semiconductor devices for switching the current to the motor, the 400 page manual can seem quite obtuse if you do not already have an understanding of how they work.  However the manual is available, which is more than can be said for some parts.)  If there is a VFD problem their maybe a Fault code displayed on the VFD LED readout?  If I recall my VFD is a Delta Model # VFD-015-E-21 (which means 015=> power rating 1.5KW or 2 HP motor, E=> VFD Series, 21=> Input power=220 1Phase.  

I believe that KA1 and KA2 are indeed small relays which are use to apply control (logic) signals to the VFD to cause the VFD to run the motor either CW or CCW.  Since you indicated that the KA1 switches on and off  but that the motor does not start you may wish to check to see if the signal via the relay is actually arriving at the VFD.  You might simply also want to try to run the spindle in the CCW direction (KA2 relay).  If by chance you have over looked it and the spindle speed is set to a low rpm the motor may not start.  The VFD speed it determined by a DC voltage between 0-10volts DC applied to the VFD via the n-Motion box.  If there is zero voltage arriving or it is very small, the motor will not appear to run.   If 10volts is applied the motor should run at maximum.  

It is not clear to me why the n-motion electronics do not apply logic signals directly to the VFD, but then I have not studied this Delta VFD operation and my info on the n-Motion controller is very limited.    I have been setting up an Hitachi VFD and electronics to run a lathe and in that VFD, if one applies both a CW and a CCW active logic signal simultaneously to both VFD inputs the VFD will actually shut down the motor if running (or not start if not already running).  The VFD inputs that are in play are probably the MI1 and MI2.  You can trace the wires from the KA1-2 to the VFD.  In my machine the wires are numbered on both ends and so the tracing is not difficult.  

If need be we could do a compare between you machine and mine.

Dave


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## rodjava (Aug 5, 2020)

Hi Dave,
I can't thank you enough for chiming in with your suggestions.  Yes, my cnc is still inop as I could not figure out why it would not fire up.  It's not like it was running and then suddenly stopped. I casually use my cnc about once a month.  This time it would not fire up at all. So I was thinking it was a breaker or relay issue.  I reset all the breakers but didn't do much with the relays because I didn't know what relays were what.  Yes, I could use just the scans of the electronics is you have them.

I'm going to play around with some of the setting you mentioned. So, thank you very much for your help.

Rod


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## macardoso (Aug 5, 2020)

Rodjava, 

Do you have a multimeter (DMM)? Can you provide some pictures of the inside of the cabinet or a wiring schematic? I'd be happy to help you troubleshoot. Shouldn't be too had.

-Mike


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## rodjava (Aug 5, 2020)

macardoso said:


> Rodjava,
> 
> Do you have a multimeter (DMM)? Can you provide some pictures of the inside of the cabinet or a wiring schematic? I'd be happy to help you troubleshoot. Shouldn't be too had.
> 
> -Mike


Mike,
Thank you too for help. Yes, I have a mulimeter.  I will track down another members pic of the electronics enclouser which might help. My cnc is positioned only 12 inches away from a wall. I had to remove both doors in order to access the breakers and what not.  So It's a real tight fit. 

Rod


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## rodjava (Aug 5, 2020)

rodjava said:


> Mike,
> Thank you too for help. Yes, I have a mulimeter.  I will track down another members pic of the electronics enclouser which might help. My cnc is positioned only 12 inches away from a wall. I had to remove both doors in order to access the breakers and what not.  So It's a real tight fit.
> 
> Rod


Mike here are some pics from other members of the same cnc.


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## macardoso (Aug 5, 2020)

OK, that's a solid start. Do you have a manual with a wiring diagram?


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## rodjava (Aug 5, 2020)

No manual, but another member, Dave, mentioned he can  send me some scans. I'm still waiting for Dave.  I'm grateful for everybodys help, so I'm not being pushy.


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## macardoso (Aug 5, 2020)

See if you can get a picture under the front cover of the VFD where the digital wires land. I expect the problem to be either A) VFD power input, B) Digital signal to VFD, or C) VFD fault.


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## rodjava (Aug 5, 2020)

macardoso said:


> See if you can get a picture under the front cover of the VFD where the digital wires land. I expect the problem to be either A) VFD power input, B) Digital signal to VFD, or C) VFD fault.


Here are some actual pics i took. Let me know what more I can add.

Also,I would like to eliminate any Mach3 issues. I normally turn on the spindle via the Mach3 control panel by first setting the speed and increments. What is the gcode to start and stop the spindle?


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## B2 (Aug 5, 2020)

Hi Rod,

Here is the scan of my PM940 CNC manual(attached). pdf pages 15 and 16 show the KA1-2 connections.  page 15 are the terminals on the n-Motion controller while 16 shows(in a cryptic sort of way TADA Inverter?) the connections to the VFD.  Note the wire numbers are 097 and 099 both at the relays and at the VFD.  Note on the manual page 16 it shows these numbers as well as the MI1 and MI2, which is the Delta control input notation. It also shows that the wires are RED via the line through the wires on page 16.   MI1 is FW(forward) and MI2 is RV(reverse) directions inputs.  The other relays, switches etc are labeled in other drawings.  Note the titles in the boxes at the top on page 13 & 14 fall to the circuits immediately below.  So for example,  see "Fan" shows Motor M4 and a power relay KM1 that also powers motor M3 which I think is the way oilier pump while M2 is the cutting oil pump.  ETC.  

The VFD maybe set up with the Default programing codes.  If so you could reset the VFD from the KeyPad.  However, if the manufacturer reprogramed it then going to the Default setup could create some real time consuming problems for you.  

Looks like after my email that a number of other folks have chimed in.  Between us all surely we can figure this out. 

The pictures you posted so a little different layout of the controls than my machine.  In mine the n-motion controller box is immediately below the VFD.  The VFD is located more or less on the upper right side of the box.  

Dave.  






rodjava said:


> Hi Dave,
> I can't thank you enough for chiming in with your suggestions.  Yes, my cnc is still inop as I could not figure out why it would not fire up.  It's not like it was running and then suddenly stopped. I casually use my cnc about once a month.  This time it would not fire up at all. So I was thinking it was a breaker or relay issue.  I reset all the breakers but didn't do much with the relays because I didn't know what relays were what.  Yes, I could use just the scans of the electronics is you have them.
> 
> I'm going to play around with some of the setting you mentioned. So, thank you very much for your help.
> ...


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## rodjava (Aug 5, 2020)

rodjava said:


> Here are some actual pics i took. Let me know what more I can add.
> 
> Also,I would like to eliminate any Mach3 issues. I normally turn on the spindle via the Mach3 control panel by first setting the speed and increments. What is the gcode to start and stop the spindle?


Silly me, the gcodes were easy to find and I tested m4 and m5. No spindle motion...... So the issue is that there is no power to the VFD at all.


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## rodjava (Aug 5, 2020)

B2 said:


> Hi Rod,
> 
> Here is the scan of my PM940 CNC manual(attached). pdf pages 15 and 16 show the KA1-2 connections.  page 15 are the terminals on the n-Motion controller while 16 shows(in a cryptic sort of way TADA Inverter?) the connections to the VFD.  Note the wire numbers are 097 and 099 both at the relays and at the VFD.  Note on the manual page 16 it shows these numbers as well as the MI1 and MI2, which is the Delta control input notation. It also shows that the wires are RED via the line through the wires on page 16.   MI1 is FW(forward) and MI2 is RV(reverse) directions inputs.  The other relays, switches etc are labeled in other drawings.  Note the titles in the boxes at the top on page 13 & 14 fall to the circuits immediately below.  So for example,  see "Fan" shows Motor M4 and a power relay KM1 that also powers motor M3 which I think is the way oilier pump while M2 is the cutting oil pump.  ETC.
> 
> ...


Dave,
Yes, my controller is mounted on the far left side and the vfd on the top right. 
Rod


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## B2 (Aug 5, 2020)

B2 said:


> Hi Rod,
> 
> Here is the scan of my PM940 CNC manual(attached). pdf pages 15 and 16 show the KA1-2 connections.  page 15 are the terminals on the n-Motion controller while 16 shows(in a cryptic sort of way TADA Inverter?) the connections to the VFD.  Note the wire numbers are 097 and 099 both at the relays and at the VFD.  Note on the manual page 16 it shows these numbers as well as the MI1 and MI2, which is the Delta control input notation. It also shows that the wires are RED via the line through the wires on page 16.   MI1 is FW(forward) and MI2 is RV(reverse) directions inputs.  The other relays, switches etc are labeled in other drawings.  Note the titles in the boxes at the top on page 13 & 14 fall to the circuits immediately below.  So for example,  see "Fan" shows Motor M4 and a power relay KM1 that also powers motor M3 which I think is the way oilier pump while M2 is the cutting oil pump.  ETC.
> 
> ...


 
In your photo 10.jpg , the l MI1 and MI2 are the red wires on the bottom left hand side of the VFD control connections. Wire labeled 097 etc.

Use the Volt ohm meter to measure the voltage at the inputs on the right hand side.  These should be the rpm speed control and one of them should vary between 0-10 volts.  One of them should always put out 10 volts and is the internal 10 volt supply on the VFD, the other will be near zero or zero.  one can connect a pot (variable resistor) between these and control the speed with it when the N-motion is not connected. 

Dave L.


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## rodjava (Aug 5, 2020)

Dave.I will test the DC voltage with my meter.  What contact points on the right hand side of the bus bar am I testing in my photo 10.jpg?


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## B2 (Aug 5, 2020)

Hi Rod,   I just saw you Gcode comment.  You can check the spindle speed with the Mach3 spindle control buttons on the front pages.  Just type the speed in and hit return on the page under the image of the pendant, then click on the button for spindle.    

Also, as far as power to the VFD when you turn on the power switch the VFD should light up and display some codes and on mine is shows the spindle is getting a forward command.  Since, the Mach-3 is not sending out a signal for a speed the motor does not run.  Also, in your picture of the control wires, 10.jpg the red wire 111 is the common line returning to the relays KA1-2.  While the 081 (small yellow wire) goes to the n-motion terminal called PWM (pulse width modulation --- modulation of the duty cycle of the incoming voltage to set the motor frequency, rpm, speed) and the small red wire (079) goes to the n-motion E-GND.   That looks like all of the control lines!    The big gauge wires with screw terminals are either your input power or the wires to the spindle motor.


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## B2 (Aug 5, 2020)

Small wires, yellow and red.  I think the yellow (PWM) is controlling the voltage and as I said above the red one is going to the n-motion EGND.  Look at the samed numbered wires at the n-motion.  My n-motion box has labels at the screw terminals.


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## rodjava (Aug 5, 2020)

B2 said:


> Hi Rod,   I just saw you Gcode comment.  You can check the spindle speed with the Mach3 spindle control buttons on the front pages.  Just type the speed in and hit return on the page under the image of the pendant, then click on the button for spindle.
> 
> Also, as far as power to the VFD when you turn on the power switch the VFD should light up and display some codes and on mine is shows the spindle is getting a forward command.  Since, the Mach-3 is not sending out a signal for a speed the motor does not run.  Also, in your picture of the control wires, 10.jpg the red wire 111 is the common line returning to the relays KA1-2.  While the 081 (small yellow wire) goes to the n-motion terminal called PWM (pulse width modulation --- modulation of the duty cycle of the incoming voltage to set the motor frequency, rpm, speed) and the small red wire (079) goes to the n-motion E-GND.   That looks like all of the control lines!    The big gauge wires with screw terminals are either your input power or the wires to the spindle motor.


Hi B2,  Yes I tested the Mach3 spindle controls and  still no motion.  When I turn on the cnc from the switch, nothing lights up on the VFD control window.


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## B2 (Aug 5, 2020)

Rod, See page 2-3 of the Delta manual for a global drawing of the VFD connections......which you can down load at:


			https://www.deltaacdrives.com/wp-content/uploads/2012/06/VFD-E-User-Manual.pdf
		









						Delta VFD015E21A VFD-E Series Drive - Buy Delta AC Drives, VFDs and Download Delta Manuals Online
					

Series: VFD-E  2 HP  1.5 KW  230 V  7.5 A  Input: 3 PH




					www.deltaacdrives.com
				




I would send it to you , but is is 12MB!


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## rodjava (Aug 5, 2020)

Because I'm old, I better ask. Should I be testing the voltage with the power on or off for a correct reading?


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## B2 (Aug 5, 2020)

Use your Volt meter to see if 220VAC is arriving at your machine and then at the VFD.  R(L1) and S(L2).  If not then you have a power problem out side the Mill.  Wouldn't you be lucky.  The VFD manual shows a fuse/breaker in line with power as recommended(?) or supplied (dashed lines around it).  Again page 2-2 of the VFD manual.


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## rodjava (Aug 5, 2020)

B2 said:


> Rod, See page 2-3 of the Delta manual for a global drawing of the VFD connections......which you can down load at:
> 
> 
> https://www.deltaacdrives.com/wp-content/uploads/2012/06/VFD-E-User-Manual.pdf
> ...


B2, Ok downloaded and viewed pages 2-3. I'm not sure what I'm looking at. Maybe because I'm getting old.


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## B2 (Aug 5, 2020)

No power, no voltage to be measured!  Just use the VOM probes to touch the screws on the VFD.  NO fingers touching anything.   

PS.  How old?


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## rodjava (Aug 5, 2020)

B2 said:


> Use your Volt meter to see if 220VAC is arriving at your machine and then at the VFD.  R(L1) and S(L2).  If not then you have a power problem out side the Mill.  Wouldn't you be lucky.  The VFD manual shows a fuse/breaker in line with power as recommended(?) or supplied (dashed lines around it).  Again page 2-2 of the VFD manual.


B2,  I will check for 220VAC.  However, I get power to the all 3 axis if this means something


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## B2 (Aug 5, 2020)

I assume you are in a house that only has 220 voltage.  page 2-2 is for 1 phase input.  page 2-3 is if you are in industry and have 3 phase power. 
 Otherwise the drawings are the same.  Top left of the VFD box is the power in .  Top right is the spindle motor connections.  Below the power in are the MI1-6 and DCM control inputs.  MI1 and MI2 are the Forward and reverse control inputs.  If one of them is activated that it the direction it is suppose tor run.


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## macardoso (Aug 5, 2020)

I’m out right now. Will chime in later if you guys haven’t figured it out.
Gcode is 

M03 (spindle fwd) Sxxxx (where xxxx is speed in RPM

M05(spindle stop)


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## B2 (Aug 5, 2020)

What value do you measure at the motor terminals?  If you have high voltage there and the VFD is not lit up on the key pad then there is a serious problem with it.


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## rodjava (Aug 5, 2020)

B2 said:


> No power, no voltage to be measured!  Just use the VOM probes to touch the screws on the VFD.  NO fingers touching anything.
> 
> PS.  How old?


64 but feels like 74. I feel like I have been slipping lately.
I will measure the voltage now.  Please stand by.


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## B2 (Aug 5, 2020)

Just so you know, even with the computor turn off (NO MACH-3) when you turn the power on to the mill the VFD should light up.


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## B2 (Aug 5, 2020)

Then you feel like me,  I am 73.   I am suppose to be hanging window shades for my wife, but this is a better diversion.  So far I have found nothing in the window area to hang the shade to!  I put a drill to it and it just sinks through the plaster!


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## rodjava (Aug 5, 2020)

I need a little clarification before I screw something up. Including myself.  Attached is my voltmeter which i set to measure ac voltage range for 220v. It's set to 500. Is this correct?  Also, am i testing the 2 red wires at the far left of the VFD in photo 10?  I assume that I ground the black probe and then make contact with the red probe in either the 2 red contact points to get a reading?

If i am wrong, please tell me in detail how to do it.  Thank you in advance.


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## rodjava (Aug 5, 2020)

I need a little clarification before I screw something up. Including myself.  Attached is my voltmeter which i set to measure ac voltage range for 220v. It's set to 500. Is this correct?  Also, am i testing the 2 red wires at the far left of the VFD in photo 10?  I assume that I ground the black probe and then make contact with the red probe in either the 2 red contact points to get a reading?

If i am wrong, please tell me in detail how to do it.  Thank you in advance.


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## B2 (Aug 5, 2020)

I am sorry Rod, I assumed you had a little more of an electrical background.  Yes, always be safe.  If you are not for sure then ask.   So for the input power and the lines to the motor we are measuring AC voltage not DC.  So the meter should be set to 500 VAC.    The smaller terminals all have low voltage DC at them.  So you would use the DC scales and the voltages we are trying to measure are under 25 volts.  The Voltages at the Relays inputs (coils) will most likely be 24 VAC or 60VAC so a 100 volt AC scale would be safe.  The output from a relay can be what ever is presented to its input.
For AC measurements there is no difference between the black and the red lead.  For DC measurements if red lead should be plugged into the red hole (+) and the black lead into the black hole(-).  Then when one connects the red lead to a positive DC voltage he gets a positive reading.   (what kind of VOM do you have?  Is it a DVM or an old fashioned needle style?)

So let me see if I have this correct.   I have gotten a little lost in the process. So let me set up some steps.

1) When the computer is turned off, but the Mill power switch is on does the VFD LED display light up? (yes or no)

2) If yes,  there is power to the VFD.  But you could still measure the inputs to the VFD to see if the power is of quality.  I assume you are running with a house hold circuit of 220 Volts 1 phase.  If so, then you should set the meter to 500 Volt AC and measure between terminals R and S (L1 and L2) on the VFD.  If you do not measure round 220 volts then the power is poor and might not run a motor.

3) If the VFD is on and the 220 input is good, then look at the VFD and see if there is a light on that says FW.  If so, then it is telling us that there is an input signal at the MI1 control input, but lets check.  Put the VOM meter on a DC scale to check for at least 24 volts DC and then connect the Red lead on the KA1 input which is the MI1 VFD control screw terminal  while putting the black lead on the terminal called DCM (page 2-2 of VFD manual) which I think is the wire labeled (111) .   You should read 24 volt DC or about this amount.  If so the KA1 is working ok.  

4) Assuming the power is of quality, and the VFD is displays are working then we need to check the control signals when Mach3 is controlling things.   For this we have to turn on the computer and run Mach3.

( will continue while you confirm the above)


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## rodjava (Aug 5, 2020)

B2 said:


> I am sorry Rod, I assumed you had a little more of an electrical background.  Yes, always be safe.  If you are not for sure then ask.   So for the input power and the lines to the motor we are measuring AC voltage not DC.  So the meter should be set to 500 VAC.    The smaller terminals all have low voltage DC at them.  So you would use the DC scales and the voltages we are trying to measure are under 25 volts.  The Voltages at the Relays inputs (coils) will most likely be 24 VAC or 60VAC so a 100 volt AC scale would be safe.  The output from a relay can be what ever is presented to its input.
> For AC measurements there is no difference between the black and the red lead.  For DC measurements if red lead should be plugged into the red hole (+) and the black lead into the black hole(-).  Then when one connects the red lead to a positive DC voltage he gets a positive reading.   (what kind of VOM do you have?  Is it a DVM or an old fashioned needle style?)
> 
> So let me see if I have this correct.   I have gotten a little lost in the process. So let me set up some steps.
> ...


I like the step by step in instructions.  Thank you.
With the computer OFF and the mill switched on, the VFD does NOT light up.
I know the mill is getting power as I can move all 3 axis controlled by Mach3 

Whats next?


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## B2 (Aug 5, 2020)

4) Assuming the power is of quality, and the VFD is displays are working then we need to check the control signals when Mach3 is controlling things.   For this we have to turn on the computer and run Mach3.  Make sure on Mach3 that the nMotion is connected.  Confirm the the spindle button is set for Forward (CW) motion.  Set the spindle speed to about half, 500, and then click the spindle button.  I assume the motor does not run.  Look at the VFD LED display and see what it says.  See if the FW LED next to to the LED key pad display is on.  Reconfirm that the VFD MI1 is active (24 Volts DC).  If all of these are true, but the motor is not running then lets check the speed signal coming from the n-Motion.  Set the VOM to measure up to 10 volts DC.  Put the red lead (+) on to the terminal with the yellow wire it should be the PWM terminal at the N-motion and the small yellow wire at the VFD (terminal 081 I think) while putting the black VOM lead on the VFD terminal with the small red wire, (079 I think) which comes from the n-motion EGND terminal.   

You should have a reading of about 5 volts DC.  If not, repeat the last measurement at the n-motion terminals to see if the n-motion box is sending out a signal at all.  If this signal is not at the n-motion then the problem is with the n-motion or the computer connection.  If there is a signal at the n-motion but not at the VFD terminals then there is a wire problem between the two.  If the signal is at the VFD and the KA1 signal (MI1) is present then there is a problem at the VFD or the motor.  

We can proceed from here after we know the answers from these measurements. 

Dave.


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## B2 (Aug 5, 2020)

VFD does not light up! Was the Line power getting to the VFD.   VOM on 500 VAC setting measure between R (L1) and S(L2) VFD terminals.


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## rodjava (Aug 5, 2020)

B2 said:


> VFD does not light up! Was the Line power getting to the VFD.   VOM on 500 VAC setting measure between R (L1) and S(L2) VFD terminals.


This is my meter and set to 500 vac. As far as measuring current, Do I simply touch the red probe individually on the contact to the R(L1) and S(L2) terminals, which are the 2 red wires on the far left of the bus bar in the attached photo? How and where do I ground the black probe from the meter?  Sorry for the very basic questions.


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## B2 (Aug 5, 2020)

The meter leads are connected correctly.  The dia is set to 500VAC which is correct for measuring the power.  We are measuring voltage not current.  The connections you want to connect to are not on this terminal strip, which is shown in this photo.  The photo shows the low voltage control signals not the power.  Look at the VFD manual page 1-3 which shows where the big screw terminals are for the input power at the TOP of the VFD, above the key pad.  The power wires should be connected to R(L1) and S(L2).  Put one meter lead on R of these and the other meter lead on the S.   The meter should show about 220 Volt AC.    Just in case there is a problem here, turn off the power to the box and make sure the screws holding these wires are tight.  I think the cover for these leads comes off if you want to look to see if a wire to the VFD is broken or loose. Other wise you can do the measurement by sticking the VOM leads points through the plastic holes to the screw terminals.


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## B2 (Aug 5, 2020)

The covers to these terminals as well as the ones to the motor at the bottom of the VFD fold down to allow you to look at them.  See VFD manual page 1-8.


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## rodjava (Aug 5, 2020)

B2 said:


> The meter leads are connected correctly.  The dia is set to 500VAC which is correct for measuring the power.  We are measuring voltage not current.  The connections you want to connect to are not on this terminal strip, which is shown in this photo.  The photo shows the low voltage control signals not the power.  Look at the VFD manual page 1-3 which shows where the big screw terminals are for the input power at the TOP of the VFD, above the key pad.  The power wires should be connected to R(L1) and S(L2).  Put one meter lead on R of these and the other meter lead on the S.   The meter should show about 220 Volt AC.    Just in case there is a problem here, turn off the power to the box and make sure the screws holding these wires are tight.  I think the cover for these leads comes off if you want to look to see if a wire to the VFD is broken or loose. Other wise you can do the measurement by sticking the VOM leads points through the plastic holes to the screw terminals.


Dave, we are making progress! I appreciate the detailed instructions as it gives me confidence.  The L1 and L2 were easy to locate behind a cover plate and well exposed.  Both contacts were easily  accessible with the 2 probes. Zero reading on the multi-meter.


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## rodjava (Aug 5, 2020)

pics


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## B2 (Aug 5, 2020)

The covers to these terminals as well as the ones to the motor at the bottom of the VFD fold down to allow you to look at them.  See VFD manual page 1-8.


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## B2 (Aug 5, 2020)

That is good news.  It means the VFD is probably ok and the problem is else where.  I will need to study the circuits a bit to proceed.   We need to find where the wires coming to the VFD originate from.  We know you have power in the box since your steppers are still working.   However, I am on east coast and it is time for dinner.  I will get back to you later tonight if possible. 

Dave L.


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## rodjava (Aug 5, 2020)

B2 said:


> The covers to these terminals as well as the ones to the motor at the bottom of the VFD fold down to allow you to look at them.  See VFD manual page 1-8.


If no power to the VFD, what should I be checking?


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## rodjava (Aug 5, 2020)

B2 said:


> That is good news.  It means the VFD is probably ok and the problem is else where.  I will need to study the circuits a bit to proceed.   We need to find where the wires coming to the VFD originate from.  We know you have power in the box since your steppers are still working.   However, I am on east coast and it is time for dinner.  I will get back to you later tonight if possible.
> 
> Dave L.


Dave,
Take your time and enjoy your meal. I'm going to sleep on it and take it up again tomorrow morning.
Rod in San Francisco


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## B2 (Aug 5, 2020)

Hi Rod,

Maybe the circuit breaker to the VFD has tripped and you just did not catch it, or maybe it has failed.

Looking at the Manual page 13 you will see the power feed to the VFD.  On the upper left hand side you will see a circuit breaker, QM, that is feeding only the VFD.  (By the way, just below this you will see the VFD that they actually call th Inverter DAP 03.  Not for sure why and it is not shown in the parts list.)  Anyway, the circuit breaker is adjustable from 5-8Amperes with a small red switch.  I know you said you tried all of the circuit breakers but just in case lets try this one again.    You did not provide a photo of it on your machine, but in the photos that you said were from a similar machine you will see it in photo  pm940 cnc 1.jpg.  It is in the row of circuit breakers (middle row) on the far left end and is small in this photo unless you enlarge the photo.  It is labeled QM.  It has a L2 and N2 feeding it with line power.  The power to the VFD comes out the bottom and the wires are labeled R and S.  You could measure the voltage between the R and S at this output and see if it has 220 VAC. If it does then the power is failing to get to the VFD from this point, but it is unlikely that both wires would break or come loose.  QM has a rectangular red button and a grey button.  When the Red button is all the way out and the grey button is all the way in (flush to the surface) the breaker is conducting and provides power to the VFD.  I suggest you check it, push the buttons in and out a couple of times, if you are uncertain if it is engaged.     You could also measure the voltage going into it to make sure that it is getting 220VAC at the L2and N2 wires.  

The hook up for these things is a little strange.  You will see in the drawing that the input has 3 terminals and that the one in the middle is connected to a wired that comes out the bottom right hand side.  The way it works is the diagram is that the N2 goes connects at the right hand terminal and come out of the bottom on the right hand side.  The wire is then connected from the bottom right hand side to the top center terminal.  The bottom left and center terminals feed the R and S to the VFD.  The reason  for the right hand side is that when the current flows from the top right terminal through the device to the bottom right the device measures the current.  If it is too large then the breaker trips stopping the current from exiting the bottom.  If it is not too large (OK) then the power feeds out the bottom R and S lines on to the VFD. 

I just went and looked at mine.  On it the little red slide switch is set all the way to 8 Amperes.  I have never had this thing trip on my machine, even when I once stalled the spindle motor and sheered off a pin on the inside.  

I do not think this has anything to do with your issue, but by the way, it is not clear to me why our machines have such a very large black transformer at the top left of the CNC box.  It seems like it is much larger than needs be and is breaker-ed below its capacity.  The best I can tell it is only to provide 60 VAC power to the stepper motor amplifiers.   This transformer is shown on the manual page 13 on the right hand side and is fuse with breaker FU4 at 10 Amps to power all of the stepper amplifiers.  For some reason, upon powering up the controller with the green start button this FU4 trips and I have to open the door and reset it.  It seems to be random as to when it occurs and I have not been able to figure out why it does this, but only on occasion.  It is a pain because if you do not realize it has tripped and you use Mach3 to change the position the origin is lost.  Mach3 does not know that the steppers are not working!

By the way if you want to see pictures of my machine look to my Feb 14th, 2019 post in the middle of the following thread.  








						PM-940M-CNC
					

Got on one the last 940M-CNC's that PM produced.  Its an all options unit with the 4th Axis, VFD, and auto oiler.  Unit also came with a small coolant reservoir, pendant, and R8 drill chuck and shell mill,  woohoo.  Used a friends bobcat with forks to move the large crates off the semi trailer...




					www.hobby-machinist.com
				




Good night
Dave


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## rodjava (Aug 6, 2020)

B2 said:


> Hi Rod,
> 
> Maybe the circuit breaker to the VFD has tripped and you just did not catch it, or maybe it has failed.
> 
> ...


Dave,
Tomorrow, I will check the voltage at the QM breaker. I will also try resetting it a few times as well. I think you are suggesting that the red tab on the QM breaker can be pushed in at different depths to control the amps from 5 to 8 amps.  I did not know this. I will also take photos of my actual electronics. Perhaps you will notice something that is out of normal. Thanks again and have a great night.
Rod


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## B2 (Aug 6, 2020)

Rod, 
No, current is not set by the depth of the rectangular Red button.  The current setting lever is very small and is located at the corner of the breaker in a black surround and is also red.  It looks like a small lever and can be set to a value of current ranging from 5 to 8 A (Ampere).  I think it has the letter "A" next to it standing for Amperes.  When these types of breakers trip it is not uncommon that you have to reset it by first pushing the off button (rectangular red button pushed in is off) in all the way and then pushing the on button (rectangular grey button) in all the way which causes the red button to pop back out.....

Dave


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## macardoso (Aug 6, 2020)

I am having a bit of a hard time following this thread so I'll post a set of tests. Feel free to skip any step that you have done already...

1. Read and understand what you are doing before you do it. Be safe
2. Set your meter to 500 V~
3. Place the black meter lead on COM and the red on V, ohm, mA (you have it right in the picture above)
4. Unplug the entire machine from the wall outlet. Lock out the connector if you can, if not just be extra safe.
5. Using your meter, measure the Line-to-Line voltage of the wall outlet (220VAC expected). Polarity is not important
6. Using your meter, measure the Line-to-Ground voltage of the wall outlet (2 measurements required, 110V expected for both). Polarity is not important
7. Set the knob on your meter to the audible continuity setting (two clicks clockwise from the 500V~ setting)
8. *With the machine unplugged, *measure continuity between the L1 prong of the plug which goes to the wall and the terminal "R" on the top of the drive (beep expected)
9. *With the machine unplugged, *measure continuity between the L2 prong of the plug which goes to the wall and the terminal "R" on the top of the drive (beep not expected)
10. *With the machine unplugged, *measure continuity between the L1 prong of the plug which goes to the wall and the terminal "S" on the top of the drive (beep not expected)
11. *With the machine unplugged, *measure continuity between the L2 prong of the plug which goes to the wall and the terminal "S" on the top of the drive (beep expected)
12. *With the machine unplugged, *measure continuity between the GND prong of the plug which goes to the wall and the terminal "R" on the top of the drive (beep not expected)
13. *With the machine unplugged, *measure continuity between the GND prong of the plug which goes to the wall and the terminal "S" on the top of the drive (beep not expected)
14. *With the machine unplugged, *measure continuity between the GND prong of the plug which goes to the wall and the terminal "GND" on the top of the drive (beep expected)

At this point I expect a few tests to have failed. Your notes state that the drive does not power up, so I do not expect that test 8 or test 10 will be successful. From what I can tell, there are a few components that sit between the VFD and the line power. These are the line reactor (square silver box) and a circuit breaker (unsure which one it is...). We need to test those.

15. *With the machine unplugged, *measure continuity between the Line side of the filter (terminal L) to the terminal "R" on the top of the drive (beep expected)
16. *With the machine unplugged, *measure continuity between the Line side of the filter (terminal L) to the terminal "S" on the top of the drive (beep not expected)
17. *With the machine unplugged, *measure continuity between the Line side of the filter (terminal N) to the terminal "S" on the top of the drive (beep expected)
18. *With the machine unplugged, *measure continuity between the Line side of the filter (terminal N) to the terminal "R" on the top of the drive (beep not expected)

Next I need you to trace the wire back from the Line side of the line filter to whichever circuit breaker feeds it. Please report which breaker it is. Also report the wire labels if possible.

With that information, I will give you some more tests to execute which will test if the circuit breaker is functioning properly. If all that works we will apply power and do similar checks again to determine why power is not reaching your drive. 

All these tests are conducted with the machine unplugged. I am trying to do this to keep you safe while you work.

-Mike


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## B2 (Aug 6, 2020)

Hi Mike, 

Rod established that there is no power at the VFD input (R-S terminals), but that there was power available for the steppers (steppers would move the table when the spindle would not turn).  This simplifies a lot.  So I identified the breaker, QM, that is feeding the VFD line power and Rod was going to test it and if it looks un-tripped then measure the line voltage to it to see if it is getting power.   It is an adjustable breaker, 5 to 8 Amp, and the spindle motor is 1.5KW so I expect that the setting needs to be near max, 8Amp.  

Rod is registered as being in CA so he probably has not returned to all of this yet.  You are in Cleveland and I am in Pittsburgh so we are up. 

Dave


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## macardoso (Aug 6, 2020)

Dave,

sounds like you guys are on the right track. Very possible the breaker could be malfunctioning or something further upstream is prevent power to the breaker.

-Mike


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## B2 (Aug 6, 2020)

Mike,  
I hope so.  There are no components between this QM breaker and the incoming power switch so, unless Rod has made a measurement error, there is nothing besides it or broken wire(s) between it and the VFD.  

Dave


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## rodjava (Aug 6, 2020)

(PROBLEM SOLVED)
Dave (B2) was right.  the problem was the QM breaker.  Even though I initially reset it a few times to no avail, I tried resetting it again with Daves insistence. Voila! the VFD turned on normally.  I'm now back in business thanks to the membership. Thank you Dave and everybody that chimed in with their help.  I hope to be a useful part of the membership in the future.

Thank you, Thank you, Thank you all!

Rod In San Francisco


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## macardoso (Aug 6, 2020)

Yay! congrats!


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## B2 (Aug 6, 2020)

Hi Rod,

Veryt happy for you.. and to have been of some help.   Pay it forward!  

By the way,  I do not know too many people who have a PM 940M CNC that is still configured as such.  Yours is one.  Mine is also, except that I moved the electronics cabinet off the back to the side so that I could access it from the front.  

So I have had a nuisance problem from day one and I am wondering if you have observe the same thing?

If I do not lock the z-axis way clamps when I power down, so the z-axis stepper does not have power, the head will slowly creep downward due to its weight.  (I figure it weights over 250 lbs.)  The cogging of the stepper motor is suppose to hold it in position, but it does not always work this way as the stepper is not large enough.  Hence, the z-axis location calibration will be lost... not to mention crashing the tool into the table or work.  If I tighten up the z-axis way clamps this creep will not happen, but I have to remember to tightening the clamps before shutting off the power.  Also, if I just have a power failure during a run or something then all is lost.  If I tighten the ways themselves most of the falling creep will vanish, but I have to regularly do this.    When I first observed this it was not too bad, but soon got worst.  At that time I also noticed that when I run the head up and down in a milling operation, like drilling, it could slowly loose position and be lower than it was suppose to be.  

Have you ever observed or had this problem?  

One way to observe this is to simply turn the power off and then tap the head with your hand a few times and watch to see if the distance to the head decreases.  When the ways are too loose and the power is shut off you can actually hear it falling as it causes the stepper to cog and the mill to vibrate a bit.    Another way is to set the Mach3 z axis zero at some reference surface, like a precision block, and then move the head up and run it up and down a bunch of times followed by measuring the distance to the reference surface to see if is still at the Mach3 zero.  I have a 1 inch precision steel block that I set the z-axis zero to.  I then remove the block and exercise the z-axis.  I then put the Mill position back to z=0 and see if I can slide the precision steel block back into position.  It commonly will not fit!

Good luck with your milling.

Dave


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