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Fanuc Ot - axis detect error

bengineer08

Plastic
Joined
Jun 17, 2022
Location
Northern KY / Cincinnati area
Hello,
I've got a Fanuc Ot lathe I'm trouble shooting, a Miyano BND-34T. It has a third axis (B-axis, a turret parallel to the Z, but on center).

It was running great for a couple years. I use it intermittently, but was gearing up to start putting it through it's paces when I got an axis detect error out of the blue.
It was a 434 Servo alarm : 3 axis detect error. Nothing would power up, hydraulics don't kick on, can't jog motors.
I started with a lot to encoder cable and motor swapping back and forth (the X and B are the same motors, so I was swapping those & the cables back and forth). I got no change, so I assumed the cables and motors were good. I've replaced what feels like almost everything in the cabinet by now.
First I replaced the drive power board (something in the manual's trouble shooting somehow led me to believe it was not getting correct power). No change.
Second I replaced the servo amp board (it's a 3 in one board, so they all got replaced at once). This now gave me an X axis detect error instead of 3 axis (B axis), also the hydraulics would now power up, and I could jog the Z and B axes, when I try to jog the X it kicks out with the error. I swapped the old board back, and it went back to 3 axis detect error (and no hydraulics, no jogging). New board back in, X axis detect error (with hydraulics and Z & B jogging ok). I figured that's progress?
Third, I then replaced the Axis control board (think that's the nomenclature, the board where the encoder cables land in the cabinet). Again, no change, and swapping the old amp board back in still gives 3 axis detect error; new board back in gives X axis detect error.
The only thing I haven't swapped out are the cables and the motors. After swapping the cables, and the motors, and all combinations of cable/motors I can think of and not getting a change, I'm not so sure that will make a difference, but I'm not sure what else to try.
It feels like I'm getting a little progress by swapping the servo amp board, but I'm still stumped with the axis detect error jumping to a different axis (and it not changing when I swap the motors).
I'm buying these boards supposedly "tested" or "refurbished" off of ebay, but I figure if they didn't work, I wouldn't be getting these same errors. And with being able to jog the other axes with the new servo amp board, it seems like something outside of these boards?
To my limited knowledge there's nothing in this circuit aside from the cables and motors.

If anyone has any ideas on what to look at that I'm unaware of, I'd greatly appreciate the insight. Thanks.
 

latheman78

Cast Iron
Joined
May 28, 2022
Location
Southern Ca Mtns.
Did you clean all the male and female plug connectors for the motors? If they get coolant in them all hell can break loose. Might as well clean all connections to the boards with a good contact cleaner also. Even if everything is new a bad connection can cause strange alarms.
 

latheman78

Cast Iron
Joined
May 28, 2022
Location
Southern Ca Mtns.
Bear in mind a lot of these older machines will give off phony alarms. I should know I have a Fanuc Ot myself. My machine is two axis and does have a dual drive board. Trying to follow what you have done, I don't see where you have verified if your power supply voltages are correct. Mine has two power supplies, the high dollar black box and the small one that runs, the contactor coils. Are their voltages correct?
 

dandrummerman21

Stainless
Joined
Feb 5, 2008
Location
MI, USA
download the fanuc alarms app. for android: https://play.google.com/store/apps/details?id=ua.dp.ptahsa.fanucalarms_v4&hl=en_US&gl=US

I think apple might have it too.


There's a lot to unpack in your post, but the app mentions for the original 434 alarm you were getting, check diagnostic 722 bits for information about what it says. this may or may not be terribly useful, but should be looked at.

I think you're now getting a 414 or 424. 414 check diagnostic 720 and 424 check 721


If those are the alarm numbers you're getting, they are functionally the same as each other (1st axis, 2nd axis, 3rd axis. if you had a 4th axis it would be alarm 444)

I also agree it might be power related. at bare minimum, voltage should be checked. I'm not sure if this alarm could be caused by a noisy power supply.

Also, what kind of drives are these? Are they alpha drives (yellow bricks) or the older digital drives (looks like a stack of circuit boards all on top of each other)
 

bengineer08

Plastic
Joined
Jun 17, 2022
Location
Northern KY / Cincinnati area
These are the older digital drives, the bare circuit board type.
You are correct, I get both a 401 (VRDY off) and a 414 alarm (X axis detect). the 401 clears when I hit reset. The 414 (Diagnostic 720), displays 4th bit. My manual says "HCAL: Abnormal current alarm (Speed control unit alarm lamp ON)" (which it is on in the cabinet). The manual troubleshooting goes on to say motor power is not correct, disconnect power to the motor and see if the alarm goes away. It does go away, I get a 410 instead (X axis excess). If the alarm goes away it says "correct connection of motor power line". I've already replaced the servo power board, the servo speed control board (servo amp board?) and the cable. So none of those appeared to be the problem.
To further confuse me, the old speed control board produces exactly the same, only 434 (B axis detect), and it wouldn't allow power to anything else (like hydraulics). The new board at least allows power (where I can still jog Z & B, and hydraulics work), but it switches the error to 414 (X axis detect).
As far as troubleshooting the power, I'm completely lost. I traced the main power in to the first transformer, and that seemed to check out as labelled, but after that I wouldn't even know where to begin checking. There were some test points on the speed control board (+15/0/+5/+15/+20) that all checked ok.
I've dug through the manual, and it doesn't really lay out where the power supplies are, or what they look like. I don't have a schematic in my manual, so I'm not sure what comes between the control transformer and the speed control unit (if anything). I've checked or replaced the power in, control transformer (T1 below), drive power board (behind SV1), speed control board (SV1), axis control board (within "NC unit" below), and the cables. I haven't replaced the motor, but have switched motors with no change.
I've looked for any LEDs on any of the other boards in there, and couldn't see any that were obviously an alarm.
Is there a power supply noted below that I'm just not seeing?

1656432706191.png
 

latheman78

Cast Iron
Joined
May 28, 2022
Location
Southern Ca Mtns.
What generation OT is your machine? Can you open the cabinets and take a picture? The voltages you list don't cover them all. I will go have a look at mine in a little while, mine is either a C or D, I always forget. Note, if I am following you it is possible you needed to change settings on your motor swap. How quick did the error come up? X & B could have been the same motors, but either with different encoders or the same encoders with different data settings. An X movement needs to be counted 2x compared to B.
 
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bengineer08

Plastic
Joined
Jun 17, 2022
Location
Northern KY / Cincinnati area
I'm not sure what generation. I think the machine is from the early 90s (manual is stamped Mar '90). Manual doesn't have much info on the control itself, but the X&B are Fanuc Model 0 and Z is Fanuc Model 5, if that helps dating it at all.

Miyano_Cabinet.jpg
 

bengineer08

Plastic
Joined
Jun 17, 2022
Location
Northern KY / Cincinnati area
well, that I'm not sure of. I can't figure which one of those crusty messes would be a 24V power supply. Any ideas where to start? The diagram in the manual isn't much help pointing out any power supplies.
 

latheman78

Cast Iron
Joined
May 28, 2022
Location
Southern Ca Mtns.
I won't edit I will add. I believe there is another area with electronics in it as I don't see any ice cube relays. Follow the cables out of the area you pictured. I had a friend that used to be 8 miles from me that had a Miyano like yours, but it is long gone. If you would have had that issue a dozen years ago I could have went over and looked at his.
 
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bengineer08

Plastic
Joined
Jun 17, 2022
Location
Northern KY / Cincinnati area
Found it. All the way bottom right on the NC control unit, a black box that plugs in like a card. I took it out completely and couldn't locate any test points that I could access while plugged in, and I'm too chicken to try it powered up while unplugged.
I'll see if ebay has any cheap ones.
Thanks a bunch for all your input.
 

latheman78

Cast Iron
Joined
May 28, 2022
Location
Southern Ca Mtns.
Found it. All the way bottom right on the NC control unit, a black box that plugs in like a card. I took it out completely and couldn't locate any test points that I could access while plugged in, and I'm too chicken to try it powered up while unplugged.
I'll see if ebay has any cheap ones.
Thanks a bunch for all your input.
The black box is only one of them, you need to find the thing I pictured, the 24V supply.
Don't buy anything yet, you are going to end up in a mess. A lot of E-bay sellers are just selling parted out machines with no idea what is good and what isn't. I have even had supposed qualified repair houses test things and say they were good and I later found out they were bad. I think you have seasoned the chili up and down too many times, it might be time to dump it and start a new batch. I think you have replaced too many parts that could have been perfectly fine.
 

bengineer08

Plastic
Joined
Jun 17, 2022
Location
Northern KY / Cincinnati area
You're right there, I'm completely in over my head here and trying anything I can think of.
There are a few ice cube type relays hidden at the very bottom, behind the rats nest of cables. There are a few more on the door, which is where the relay board is. I checked behind that tan panel and nothing there. There are two blue wires at the top of the relay board that I could trace back to the black Fanuc power supply box, and those checked out at 24V. So I'm guessing the Fanuc power supply is okay? I truly can't find any other power supplies, unless they're integrated into another board somewhere? I've played around with various power supplies on many projects in the past, so I am familiar with what they should look like, but I'm stumped here. Could it be possible that they used all of their 24V in the machine from that one Fanuc supply?

Miyano_Door.jpg
 

Ox

Diamond
Joined
Aug 27, 2002
Location
West Unity, Ohio
IDK about this generation of equipment, but 90's and newer Fanuc amps would have their own 24, and then there would be 24 for "the machine" to run I/O.


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

Think Snow Eh!
Ox
 

latheman78

Cast Iron
Joined
May 28, 2022
Location
Southern Ca Mtns.
There are often both 24VDC and 24VAC needed in CNC equipment. Most of those ice cube relays run on 24VDC, and there are a lot of contractor coils run on 24AC. You also need to be leery of bad grounds that can cause havoc. Have you documented and taken pictures of everything you have done? Can you put it back to where you started? Don't worry about feeling you are in over your head, we have all been there and done that. If the world's best CNC tech came to work on your machine he could ending up running around in circles just like you are, but he would lay a big bill in your lap.

The issue is with these older machines even if you unplugged something that was working fine and plugged it back in it may do work the same, due to corrosion and old brittle dirty connections.
 








 
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