VQC-20/40B M2 Z axis alarms

[nlh]

Hello,

Looking for some advice on 2 alarms that popped up today on my Z axis. One is a "25 NMI SERVO DRIVE ALARM", the other is a "15 DRIVE ALARM Z AXIS. The machine was running but idle with the Z and Y axis at machine home positions. I stepped away briefly to eat lunch and about 10 min later I heard a loud bang like a gun going off. I have some parts to get out so now I'm in a pinch.

Today has been very humid with temps in the 80's. I thought I had some issues earlier with humidity so I had the doors opened and a fan blowing air directly into the cabinet (maybe not a good idea?) Should also note that with power off I can't feel anything very hot on the drive or boards, a couple spots are warmer, especially around the larger white resistors. Also a definate hot or burnt electrical smell.

I checked all the breakers and fuses I can find but still a no go. Maybe there are some thermal breakers hidden somewhere that I can't see? Tried leaving the machine off for 10 min and starting it back up but still nothing.

Also, if this is any help, generally when the Z axis is at rest at machine home, the Z load meter will pull about 20 - 30% load. However when I move the axis down closer to the table, the load drops to 10 - 15% or less. I installed the machine in 2007 and it has done that since that time. Could there be a problem here as well?

Thanks in advance,
Nate

[onthebumper]

First you need to check what type of drives you have. They will either be TRA or TRS. There are a series of LED's on these drives that will tell you what the alarm is.
Here are the manuals showing the alwarms
TRA - http://www.meau.com/functions/dms/ge...00000465000000
TRS - http://www.meau.com/functions/dms/ge...00000465300000

[nlh]

The top LED bar has DBL and P.OFF on (red color).

The side LED bar has OCP lights on.

Upon further investigation of the drive itself, I found that at least 2 of the capacitors that are located beside the transformer (33mf, 350V) were blown, also the traces that go the the N and P locations on the screw terminal bar were melted off. This must mean that there is a short somewhere, correct?

I traced N and P back to the power unit located below the drives (I think the MEAU manual calls it a capacitor unit). However all 3 drives are wired in parrallel so I would think that if there was a problem here, X and Y would be blown too.

Possibly a servo motor?

I have another drive that I was able to pull from a known working machine, I just hesitate to put it in until I can verify that the problem isn't external to the drive.

Any idea where to go from here onthebumper?

Thanks again,
Nate

[onthebumper]

Yes it a good idea not to replace the drive until you know what went wrong.
The motor may have become shorted. Pull off A and B wires from the drive and ohm them out. You should get infinite resistance to ground and 10 meg or higher between each lead.
Check the brushes on the motor and make sure they look good. When you pull the brushes out stick an airgun in the slot to blow out some of the built up carbon dust.

[nlh]

Ok, Measured between A and B. Got a reading of .8 ohm, not K or M ohms, just .8 ohm. Measured between A - Ground, B - Ground, initially got 15.5 - 15.6 Megohms.

I then pulled 1 brush (can't get access to the other 3 unless I tear basically the whole head apart) and blew it out. Got a little bit of carbon dust but not a large amount. Brush looked good, was not stuck or gooped up. After this got a readying of 1 ohm across A - B, and infinite resistance between each leg and ground.

Also decided to try the same measurement for X and Y, got a reading of 1.3ohms A-B on X, and 1.2ohms on Y. Infinite resistance to ground between each leg on both drives.

Do these numbers sound correct?

[nlh]

What does lines G1 and G2 do? I see from the maintenance manual that they go to the motor, but I don't see any description. Resolver, tach, etc?

[onthebumper]

G1 and G2 are for the motor overheat. You should read a dead short on them. When the motor overheats they will become open or infinite resistance.
The readings you are getting are not great but they are not terrible either. They are not readings that would make the drive blow up the way it did.
I would give Mitsubishi a call and see what else you can check out. It sounds like the motor is ok but I would be hesitant to swap the drive until talking with them. You can also see what the cost of a replacement unit or repair is too. 847-478-2500

[nlh]

Thanks again,

Looks like I've got some phone calls to make.

In the meantime I am working at switching over the jobs to another machine. Unfortunately, the machine went down with one of the tool holders I need still in the spindle.

Do you know of a way to manually unlock a toolholder from a VQC?