Miyano KNC 45 has a ghost electrical issue

We've had this machine for a bunch of years,runs great for weeks and months . it runs production work mainly small stuff. it repeats and holds tenths all day everyday.

but these little bugs keep popping up at the wrong time and they make no sense.

Problem #1 is the z axis will shutter then kick off the Z drive with a over current alarm. sometimes once a year or month sometimes ever f'd day. just have to restart it and it runs.
this could be when its just sitting there or actually moving. it has a minds of its own. Ive cleaned and check brush's all conections and it still happens.

problem #2 spindle drive. if the power goes off or I have to shut it off to reset the x drive. I have to turn the main power on and off maybe up to 20 times just to get the spindle drive to come up with no led errors. led 123 on a fenric 5000 v2 type fsd-11ar-22

problem #3 spindle drive sometimes when you go to start spindle it comes up with a start failure when you turn the spindle on. this is alarm led 1 same drive. I was told that its either the speed voltage control reading negative or motor feed back, also said more then likely a loose connection on the 16 pic cable.

problem #4 spindle drive for live tooling.(separate drive from main spindle drive) sometimes get an error when turn rotating tools on. if I do I let it set for one hour and it starts up just fine and runs forever or untill I shut the machine off on the main power.

I been leaning toward loose wires due to the age but I haven't found any in the last 5+ years. you guys have any ideas on what to look for?
problem 1 2 and 4 shouldnt be tied together all different systems as near as I can tell as they really aren't connected to each other or relate to one another. but I'm not sure. could they be?

back in dec this did the same thing then ran since Jan problem free up until the last week.

Edit Forgot to add
problem 1 I looked at the following error on dig/prm 800 and 801 800(x) hold 1's and doesnt flicker. 801 (z) goes between -4 and -3 constantly. Tried to adjust offset pot and made no differnce. gain and tach pot no difference either

I have a machine that did similar stuff with spindle drive.

The issues would be real bad on startup sometimes, but occasionally it would come out of nowhere.

I started keeping a log and it was the worst when it was very rainy and really didn't happen in the late summer dry season here. It was also in the home position a lot when it happened.

I meggered the spindle motor through the cables off the drive and it tested bad so I replaced the spindle motor. Same problem. I pulled the cables off the motor and the drive and meggered just the cables and they were shit!

New power wires to the motor and all has been good for years.

I've found a megger is very useful troubleshooting tool for old CNC's.

Cleaning all connections and resetting boards is the first thing I would try and it appears you did that. Intermittent variable alarms has always been the result of a bad connection or cable for me. The worst ones that drove me nuts were on a Fanuc OT, it would run for months and then all of a sudden axis shudder and alarms for excessive torque or whatever it was. Sometimes it would have just a single alarm on Z (It was a lathe) or sometimes a group of 6 alarms between X & Z. Finally one day when a reset would only clear it for an hour or less at a time I started digging. The culprit was the 20 some odd pin connector on the Z-axis encoder had moisture in it. What was strange it was even throwing up X-axis alarms. Since you have cleaned all the connections I would meter the cables like Garwood suggested. Good luck, I know how frustrating intermittent alarms can be.

Just want to point out that a multimeter is not a megger. A lot of stuff will test just peachy with an Ohmeter, but you put a megger on it and you get the real story. A megger injects high voltage into the wire/windings.

Garwood said:

I have a machine that did similar stuff with spindle drive.

The issues would be real bad on startup sometimes, but occasionally it would come out of nowhere.

I started keeping a log and it was the worst when it was very rainy and really didn't happen in the late summer dry season here. It was also in the home position a lot when it happened.

I meggered the spindle motor through the cables off the drive and it tested bad so I replaced the spindle motor. Same problem. I pulled the cables off the motor and the drive and meggered just the cables and they were shit!

New power wires to the motor and all has been good for years.

I've found a megger is very useful troubleshooting tool for old CNC's.

Click to expand...

we have control temp, I had thought about that as well so kept the cabinets open. back in the day with the old mutil layer boards humidity used to effect them too.

I havent traced any wires yet, that going to be next.

Dualkit said:

Cleaning all connections and resetting boards is the first thing I would try and it appears you did that. Intermittent variable alarms has always been the result of a bad connection or cable for me. The worst ones that drove me nuts were on a Fanuc OT, it would run for months and then all of a sudden axis shudder and alarms for excessive torque or whatever it was. Sometimes it would have just a single alarm on Z (It was a lathe) or sometimes a group of 6 alarms between X & Z. Finally one day when a reset would only clear it for an hour or less at a time I started digging. The culprit was the 20 some odd pin connector on the Z-axis encoder had moisture in it. What was strange it was even throwing up X-axis alarms. Since you have cleaned all the connections I would meter the cables like Garwood suggested. Good luck, I
know how frustrating intermittent alarms can be.

Click to expand...

the cables might be it for the z axis issue as the Miyano ha some odd tight bends in the motor cables.

the spindle issues i'm leaning towards connections. even ordered a case of contact cleaner. might be a long weekend. its been running all day since 6am with not on issue( and I shouldnt have said that).
On the spindle drive I am also going to reseat the board and all connections.
I havent taken any ribbon cables loose yet. moisture is usually the problem on machines and it could be on this one.

Garwood said:

Just want to point out that a multimeter is not a megger. A lot of stuff will test just peachy with an Ohmeter, but you put a megger on it and you get the real story. A megger injects high voltage into the wire/windings.

Click to expand...

now i understand what a megger is. I'll have to look at that once I get past everything else. Thank you

megger = mega ohm meter. It's designed to measure very high resistance, and it does it with relatively high voltage. Generally, the more you pay for a megger, the higher the voltage is uses for the measurement. Higher voltage is more important for measuring really long wire runs, for example, like in conveying systems in mines. It is not as important for machine tools, but more volts/more better I suppose.

Anyway, the megger is typically used to check resistance between a conductor and ground, such as a motor winding and the actual motor frame. If the insulation is in good condition, the resistance should be infinite, meaning no current can pass between the conductor and ground. The lower the resistance, the worse the insulation is. A dead short would be a complete failure of the insulation. FWIW, I've checked several motors that showed almost a dead short with a megger that were still running.


This sounds like an old machine so it's hard to say where one should start. The fact that the issues move around certainly makes it hard to pin down.

I have meggered many motors especially ones that sat unused for a long time or got wet. On a 480 volt motor you need a minimum of 1 megohm of insulation resistance to be sure won't just go boom when you apply power. Below that you need to dry it out or send it out for a dip and bake before it fails. When drying a motor out the resistance goes even lower as it drys then will rise as it gets completely dry. If you have more than 1 Megohm you can safely start the motor and it is a good idea to just let it run for a long period of time as that will dry it out. Biggest wet one I worked on was 1 megawatt generator that got flooded. Used an 800 amp DC welding machine to put current through the windings and dry it that way. Took about two weeks.

ewlsey said:

megger = mega ohm meter. It's designed to measure very high resistance, and it does it with relatively high voltage. Generally, the more you pay for a megger, the higher the voltage is uses for the measurement. Higher voltage is more important for measuring really long wire runs, for example, like in conveying systems in mines. It is not as important for machine tools, but more volts/more better I suppose.

Anyway, the megger is typically used to check resistance between a conductor and ground, such as a motor winding and the actual motor frame. If the insulation is in good condition, the resistance should be infinite, meaning no current can pass between the conductor and ground. The lower the resistance, the worse the insulation is. A dead short would be a complete failure of the insulation. FWIW, I've checked several motors that showed almost a dead short with a megger that were still running.


This sounds like an old machine so it's hard to say where one should start. The fact that the issues move around certainly makes it hard to pin down.

Click to expand...

its a late 80s machine I believe.
what I think is there is 3 problems. one the spindle drive 2 the z axis drive and 3 the live tooling drive. They are all seperate systems persay.
and most likely because of being wet or dirty like others suggested.
going to start on the z axis 1st. Think I am going to swap X and Z drives to see if its a drive issue or a wiring/motor issue.. once thats fixed I'll tackle the spindle drive.

garyhlucas said:

I have meggered many motors especially ones that sat unused for a long time or got wet. On a 480 volt motor you need a minimum of 1 megohm of insulation resistance to be sure won't just go boom when you apply power. Below that you need to dry it out or send it out for a dip and bake before it fails. When drying a motor out the resistance goes even lower as it drys then will rise as it gets completely dry. If you have more than 1 Megohm you can safely start the motor and it is a good idea to just let it run for a long period of time as that will dry it out. Biggest wet one I worked on was 1 megawatt generator that got flooded. Used an 800 amp DC welding machine to put current through the windings and dry it that way. Took about two weeks.

Click to expand...

you saying the motor can be wet inside? i''l have to check that out also thanks