tips for safely working on motor drives?

[Cole2534]

Looks like my lathe spindle drive is on the fritz and before I spend $2900 to have it repaired, I'd like to remove some of the components and test them myself. The manual shows what values you need and I have the tools, but what I don't have is the experience.

Can anyone share some tips for working on these drives safely, both for me and it? Do I need ESD protocols? How is the best way to discharge the capacitors? Things of that nature.

Thanks, Cole

 

[JST]

1) You probably do not want to remove and test anything before you do an overall assessment.

2) I have seen many jump in as you are suggesting. Normally it does not end with success.

3) Experience is important. You need to know or be able to infer a lot past the schematic. What you expect to see at a point, vs what you actually see, etc. A test sequence is also important, the manual may or may not have that. The best is a troubleshooting sequence, to determine what is working and what is not, PLUS a test sequence.

4) ESD yes. REsistor of 10W and a couple or 3 k ohms will discharge capacitors, in some cases of high power, a 100W is better, depends on the potential stored energy. You do not know if the internal discharge system is working.

5) the downfall is usually that some programmed part is bad. (depends on what sort of failure you have). You won;t have the program even if you can get the part.

6) Try all the stupid simple things first.... You probably won;t be able to fix the more complex issues anyway.

7) I have designed a number of VFDs, that were made in volume. I'd have to need that drive pretty badly and have the time to fix it, before I'd dig into it.
It was bad enough fixing prototypes that I knew everything about and had every part available for. And I've done a lot of troubleshooting and fixing over a 45 year career in design, I'm not shy of doing it..

 

[Cole2534]

1) You probably do not want to remove and test anything before you do an overall assessment.

2) I have seen many jump in as you are suggesting. Normally it does not end with success.

3) Experience is important. You need to know or be able to infer a lot past the schematic. What you expect to see at a point, vs what you actually see, etc. A test sequence is also important, the manual may or may not have that. The best is a troubleshooting sequence, to determine what is working and what is not, PLUS a test sequence.

4) ESD yes. REsistor of 10W and a couple or 3 k ohms will discharge capacitors, in some cases of high power, a 100W is better, depends on the potential stored energy. You do not know if the internal discharge system is working.

5) the downfall is usually that some programmed part is bad. (depends on what sort of failure you have). You won;t have the program even if you can get the part.

6) Try all the stupid simple things first.... You probably won;t be able to fix the more complex issues anyway.

7) I have designed a number of VFDs, that were made in volume. I'd have to need that drive pretty badly and have the time to fix it, before I'd dig into it.
It was bad enough fixing prototypes that I knew everything about and had every part available for. And I've done a lot of troubleshooting and fixing over a 45 year career in design, I'm not shy of doing it..

You are just the man I was hoping to reply!

This drive is an old Mitsubishi Freq-Rol FR-SF in my QT15n and every once in a while it tosses random alarm for phase loss, insufficient voltage or another error that has escape my mind. I have good voltage going to the machine and these are only spindle errors, they don't show up on the axis drives.

I think I'd like to get in and test the capacitors to see how they measure.. There are (5) 3200uf 350vcd units that bolt into place so that should be fairly straightforward. I'll round up a resistor to safely discharge them.

If the caps test good the manual also has a transistor test I'll do. If those components test good and nothing is loose/burned/visibly incorrect then it'll go to the drive shop.

 

[JST]

Oh, it is "working" but has intermittent faults show up. That's MUCH better in some ways, less good in others.

The good: Everything is capable of working, so there are no damaged parts, nothing shorted, no holes burned in the PWB, etc.

The bad: Intermittent failures are often a real pain to find. I'd consider using a good contact cleaner on any pin and socket connectors, and checking all the mechanical connections. If possible, give the PWB a good look all over to see if there might be cracked solder. Pay special attention to solder joints on connectors, heavy parts, etc.

You probably cannot find the divider string of resistors that determines voltage, and also may detect phase loss (via ripple voltage). You will have to depend on eyeballing everything in that case. Maybe the manual can help.

For the errors you mention, checking capacitors is a good plan. Excess ripple voltage, due to low capacitance, can cause the two errors you mention. So can problems with the divider chain that I mentioned above, or solder problems.

You seem to be off to a good start. I would not take out anything but capacitors, as far as parts, since part problems other than capacitors are not the most likely cause, in my opinion from the far end of the internet. Eyes directly on the unit may suggest otherwise.

The problems I mentioned may be caused by temperature or by vibration acting on cracked solder. "Freeze mist" is often a good way to check for that sort of issue, as often cold will open up the bad joint. Sometimes it does the reverse, though.

If you try freeze mist looking for bad solder (if capacitors seem good), try hard to not freeze optoisolators or microcontrollers. The temperature of the mist can be quite cold, and both of those may do odd things when very cold.

Watch out for the mist causing condensation of water. That can make connections in high impedance circuits, often on the reverse side of the PWB. Those may cause really strange behavior, so don't overdo the mist.

One more thing.... in a vibration environment, screw-terminal bus capacitors may chew away their contact pads. You might need to add a flat washer and/ or fix the copper pads. Might even have to make a custom size, depending.