Makino FNC 60 Servo Alarm "VRDY OFF"

[GBeaman]

My trusty Makino failed yesterday. I am getting this alarm 401 SERVO ALARM: (VRDY OFF)

I spent the afternoon evening trying to narrow down the problem. The machine will fire up and run until something warms up and then it shuts down (no more then 10 minutes of up time). It can cool for a period of time (30 minutes) and then will likely run another 5minutes before faulting out again. There are no other lights or errors on the drives, and I have turned off the servo driven tool changer in the parameters for the purpose of trouble shooting and eliminating its drive as the problem.

These are Fanuc OMc controlled AC red cap motors (1992). The servo drive for the XYZ axis is all combined into one unit with a top board. I have removed the top board and found the MCC contactors in the drive. I pulled the cover off of them and sprayed freeze it on them to see if maybe a coil was going bad in the MCC contactor itself, to no avail. When warm and the error is reset the MCC contactors pull in momentarily and the DRDY led is lit on the drive, and then it drops back out.

I need to form a plan of action. I guess that a Servo motor itself could be the problem, or the drive unit. If it is the drive unit MetalTech recommended Redrive services for another issue. I am thinking of pulling it and sending it to them for further evaluation. However, if I am wrong, I may turn a simple repair into a much larger ordeal. Any help or pointers to get closer to the cause of the problem would be helpful. Thanks.

Also, if anyone knows of a trust worthy technician in the central Texas area, I would love to find a contact.
-Greg

 

[Dustyjoe23]

Hello,
I've got the same machine. What kind of conditions are you running when it alarms? Spindle load? Feed rate? There is no axis load indicator which makes it hard to tell if you are overloading the servos. Are you running a 4th axis? Most of the time I've run into that type of alarm it's been a limit switch. One time it was an improperly sharpened spade drill that overloaded the z. You might look through the "ladder" and see if they are all working right. I've got a guy here in easy Texas that helps me diagnose. Not sure if he travels to marble falls. Do you have all the books? Back to the fourth axis. If the brake is on and you try to rotate it will alarm. Hope this helps.

 

[alphonso]

Pelican Industrial
8550 Westland West Blvd.
Houston, TX 77041

Tel: 832-678-4806
Tel: 832-678-4807

pelicancnc.com

This guy is a wizard. Had a spindle drive problem with an 0TC. We took it off machine and carried it to him on a Saturday. He looked at it, replaced a few things that were obviously(to him) bad and followed us back to Lampasas. Put it back in and started going thru its paces to see if everything was okay. It wasn't, so he carried it back to Houston. Comes back on Friday, puts the drive in, everything is a-okay.

Be aware that he is hyperactive(manic) with a pretty abrasive personality.

 

[GBeaman]

The condition that it occurs in is irrelevant. It will occur at a time interval whether mid running a light cutting program or just sitting still. Seems to be only a time related issue. The 4th axis drive is the servo running the tool changer. It is turned off, in case it could have been causing the trouble. I found a local guy, I have no idea how fast he is. But I will give him a shot. Right now, I am running these parts on the old Bostomatic. It is slow, but beats no alternatives...
Alphonso,
Thanks for the tip on the tech. I knew there would be folks in Houston and Dallas. Maybe I could ship him my drive or something, but a 4hr drive each way sounds expensive. Hopefully the guy I found will be sharp. Are you in Lampasas. That isn't too far from me, maybe an hour?
Thanks,
Greg

 

[alphonso]

T
That isn't too far from me, maybe an hour?

Only if you walk. 35 minutes, as a rule.

Pelican is about 4 miles East of FM1960 US290 intersection on far west side of Houston. About the least painful place to try to go to in the whole friggin' town.

 

[Admin5]

Have you reseated and/or used Stabilant on all socketed IC's ? On my FNC 60 there were at least two socketed IC's on the motherboard that were impossible to get to* until I made a long screwdriver into a miniture pry bar by bending it at the tip with torch, and one of those IC's turned out to be the culprit. (not for this exact problem of course....but something equally quirky)

*impossible unless you removed many other boards attached to the motherboard, which I wanted to avoid doing like the plague.

Milacron

 

[metaltech]

Check the wiring diagram for the E-stop string. A 401 is a generic "servos went off when not expected" usually due to a broken E-stop string. I would think about a dirty contact in a limit switch, E-stop switch, breaker, thermal overload, etc., anything that might be in the string. Use a meter to check the resistance in the string. Usually last in the string is a relay, so that relay could be losing coil power, or the relay could be bad.

If not above, you need to put some components through some thermal cycles. This could be a connection or bad solder joint (though generally those problems improve with heat) or a discreet component on a board. Since it normally runs about 10 minutes from cold before the problem, try warming the control boards and the servo drive with a hair dryer before starting. Only do one of those, power up the machine, and see if anything has changed. If not, after a good cooling (overnight), warm the other stuff and try again. You need to induce a change in the behavior in an area, then narrow it down. Yes, a bit tedious. If you do make a change, now chill that area with the freeze spray and see if you delay the 401. Often you can narrow it down to a certain board, and I've found individual bad chips this way. Careful with the heat and the freezing. Keep them both moving, or you can cause more damage.

 

[GBeaman]

Breaking the E-stop circuit causes a different message, I think "not ready" message on the screen. I had ruled out E-stop in my mind because, I thought to myself, "How would the control know where the e-stop circuit was broken?" Maybe, however there would be a difference in breaking the e-stop circuit at, say a limit switch or the ending relay, as opposed to the e-stop button on the operator panel or the tool changer panel. So can a 401 be produced by the E-stop? If it could be as simple as a limit switch I could very well see some sort of contamination causing a stick in the switch. This is a whole other avenue that I had not considered. It would also explain why the servo drives show no errors on them when in a control alarm state. However, if it were a limit switch it probably wouldn't be time sensitive. But, the ending relay could have a coil that very well might be time sensitive.

Hmmm. Component replacement sound much more palletable to me then rebuilding drives, at this point in my bank account. :-) Thanks as always, metaltech, for your wisdom!

 

[tjspann]

We had issues once that turned out to be a cable connector failure. The replacement cable was pricey and the service dept. asked if we had tried to re-solder the connection. We took the cable connector apart and patched it ourselves. Cheap and relatively simple, takes two people to complete.

 

[metaltech]

This could get ugly, Greg. Yes, an E-stop condition would usually mean a NOT READY. I have seen a 401 alarm without the NOT READY, but I don't think it was a 0 control.

The control has to put out a servo-on command to the drives, then they have to turn on and answer quickly that they are operational. An interruption in the command could cause the drives to shut off, obviously. But, a dropping of the servo-ready signal back to the control would result in the command signal turning off. IOW, if the servo-ready signal went bad, the CNC thinks there's a drive problem (even if they are good) and shuts them down. Chicken and egg thing going on.... The CNC servo-on command has to go to the I/O board or some type of relay before sending the 100VAC to the drives that turn on the internal contactor. So, it could be a poor connection on any related cable connector, or a bad I/O board, relay or the drive contactor. Unplugging and replugging the connectors is easy, as is checking any screw-down connection. I still think you need to heat/cool the boards to see if there is any change. Yep, tedious work. Start with a 6er of St. Arnold or Rahr to make it more tolerable!

 

[Milacron]

Hmmm. Component replacement sound much more palletable to me then rebuilding drives, at this point in my bank account. :-) Thanks as always, metaltech, for your wisdom!

For my curiosity, are you ignorning my comments about reseating (or Stabilant application) any IC's in sockets because you have already done that or because you don't think it will work ? If the latter, I can relate as I tried it numerous times early in my "career" and it didn't do a bit of good.

But I kept at it and have found that to fix some pretty bizarre problems many times in the past five or so years, so it's always worth a try. If there are alot of socketed IC's that are difficult to get to, using Stabilant in a syringe like bottle with two inch long needle is way faster and less likely to damage anything...i.e. you don't have to reseat the IC, just squeeze a bit of the liquid on the IC legs and it will soak in the socket and do it's thing.

 

[Ox]

I had a 401 on the 18i this summer, and it turned out to be the Power Supply.

(Not to be confused with "the" 401 for you Canucks.)


Good post Milicron.
I gotta say that I have never found that to help either, but your reasoning is good to keep in mind.


----------------

Think Snow Eh!
Ox

 

[Milacron]

Good post Milicron.
I gotta say that I have never found that to help either, but your reasoning is good to keep in mind.

I don't keep a diary but I'd say IC reseat/Stabilant has absolutely for sure, fixed at least a dozen CNC machine control problems I've owned over the past five or six years.

 

[GBeaman]

I really wasn't ignoring your post. I spent a day or so trying to diagnose/fix the problem before deciding that I wasn't going to fix the machine quick enough to use it on the part run that was on it. I had to tear it all up and move it over to the slow as dirt Bostomatic. I might finish my part run today, and at which time I will try to figure out what to do next. I had, falsely, decided in my mind that the drive was the probable cause of the failure. According to all the insight here, it very well may not be the problem. The ICs you speak of on the mother board, I can only imagine where they are. I need to dig deep into the cabinet to even locate them. I do share the sentiment of FEAR when talking about prying on a mother board or IO board. Sounds like I could really jack something up. Even without a physical breakage, what about static electricity? It is interesting to hear that you have fixed so many problems, though. Thanks for the advice. I will update this post when I have some more information.

 

[GBeaman]

Some updates and more specific questions...
Milacron, I reseated the 2 ICs on the mother board you suggested without any change. There are some more socketed ICs on the PMC (I think that is the label) board. I didn't remove the board to reseat them yet.

Just to correct myself. There is a "not ready" that accompanies the 401 alarm. I am sorry for being mis-leading, but hopefully this will make the diagnostic process easier.

I pulled some covers to look at the limit switches. Yup, there they are... You can push one of the 4 buttons on each axis to reset the Estop. Of course when hot, it will only momentarily energize the drives before dropping back out.
So, I guess I need to figure out the E-stop string. I found a clear plastic larger 24v relay in the rear cabinet labeled EMG. I pulled it out of curiousity and it was warm. Not hot just noticeable. Anyways, the coil is always energized. When you pull it clicks and stab and it reengages. Is this the location to start looking into the Estop circuit. I will go study my diagrams some more, but I am not sure I understand the circuit drawings well enough to trace the Estop circuit. Thanks fellas.
-Greg

 

[metaltech]

Greg, the EMG relay should always be on. When the string is broken, it will go off. The NOT READY and the alarm 401 usually are together. But, if it is in E-stop, that EMG relay wouldn't likely be energized. Perhaps it's wired differently than most other brands.

On reseating chips, try to be aware of what you're reseating. Many of the System 0 controls had some of the RAM socketed. If you pull the chip, you'll lose the memory.

If you need help on the schematics, take some pix and e-mail them to me. Or, send them from your phone to mine.

 

[GBeaman]

I had a local tech come out for a few hours on Saturday. He was a nice and knowledgeable guy. We looked and tried and tested several things. He left as stumped as I am. He said if it were his machine he would pull the XYZ axis drive and send it to Fanuc for evaluation.

What tested good was:
Estop circuit
The 100V input to the drive
The 24V input to the rest of the NC circuits
The motors "meg" good through the cabling, hopefully eliminating a cable or motor problem.

He said when he looked at his Fanuc diagnostic info that it suggests an internal problem with the drive or a possible problem with the CPU.
It is weird that it is getting VRDY off and the Estop circuit isn't dropping out. The 24VDC is always present and the 100V AC never drops out either... At least we couldn't see a flicker or change in voltage of any kind, using the multimeter, while it faulted out. Once we even ran it until it faulted while holding down the OT release button to see if one of the over travel switches was failing. Still failed like clock work.

I think that I will pull the drive and see if I can't OHM out the coils in all 5 of the MCC relays in the base unit. I may have to desolder them to check them. Then I guess I will mail the whole unit out for evaluation if I don't see or find anything.

 

[Milacron]

On reseating chips, try to be aware of what you're reseating. Many of the System 0 controls had some of the RAM socketed. If you pull the chip, you'll lose the memory.

Loosing memory was why I was afraid to pull any boards. I've reseated a gazillion IC's in my day and never had a memory loss issue. Then again I suppose it could happen.... which is another good thing about Stabilant...you don't have to pull the IC, just apply a drop or two as you swipe the applicator across the IC legs where they fit into the socket. If there is a microcorrosion problem on the IC legs Stabilant will fix it.

GB, the offending IC's on my FNC60 were on the exposed area of the motherboard in between the last single board to the right and whatever module follows that. Too narrow a gap and too deep to get to with Stabilant (i.e. I couldn't get my hand in that narrow a gap) so I bent a long small screwdriver to serve as mini pry bar to reseat what was there. Don't remove the IC...just pry one end of each IC, push back and then pry the other end and push it back. You don't dare pull one out too far as you might bend a leg pushing it back in.