Fanuc problems need help

[R.thayer]

I own a turning center with a 3 tc. The control power supply stopped working about a year ago and I just got a used one about a week ago. I installed it and the control came to life but not without it issues. First I had working memory parity problems so I dumped the memory and mdi the parameters in. This got rid of the memory problems but now the latch relay built into the power supply is not working. I would like to know how this works. I have tested all output voltages from the power supply and they are with in limits stated in the manual. I even turned the 5 volt pot up to get it closer to 5 volts. No luck I would like to know if the 5 volt logic signal for the latch relay comes back from the control? The machine will not do anything it tells me on the crt not ready. I can't find out much about this in the manual. I am guessing that is has something to do with the latch relay not stating kicked in. I can make the control stay on without the latch relay by holding the enable button on the front of the machine in. That is when it tells me not ready. So if there are any Fanuc service guys that read this please let me know what you think. I can get to the ladder so I should be able to see inputs and outputs. Also I have looked at the E stop input and it is low so I am guessing that it is not that. Any ideas will help me out so please responde if you know anything about this. Thank you for your time and hope to hear from you very soon. I would love to fix this problem as this lathe is a really good machine.

[Al_The_Man]

The E-stop input is active low, so 0 means it is active.
Also check the 24vdc output from the supply.
There were different model versions of the 3, some provided for an E-stop output also active low.
There is also diagnostic 700 ~ 702 that will tell the status.
Check the servo's overloads are not tripped.
Al.

[R.thayer]

Where are the servo overloads located? Also what do you mean about the e stop signal? I checked the 24 volts coming from the control power supply and it was about 23.89 volts. Thank you for the help.

[Dan Fritz]

I've been studying the only 3T/3M schematics I have (they're very old), and here's what I've learned so far:

When you press the "ON" button, RY31 on the power supply is supposed to pull in and hold itself on through a set of it's own contacts. Other contacts in RY31 permit current from the main rectifier circuit in the power supply to pass through, and power the whole power supply board.

The "OFF" button is normally closed, so a bad OFF button can also prevent RY31 from holding itself on.

If the power supply's fuses and rectifier circuit is good (and your voltage checks confirm that), then there are only three things that can prevent the power supply from staying on: One is a bad RY31 relay, second is an "open" OFF button, and the third is an overcurrent condition of some sort. There are several circuits on the power supply that can shut it down if the voltage or the current draw is out of range. It also looks like another relay (RY32) can be also triggered by an "external" alarm signal, which can shut things down too.

I suggest that you disconnect the DC output from the power supply, so there can be no excess current load. If the power supply stays up, then you're likely to find a shorted limit switch or something that's using too much current. If that's not it, look for a bad OFF button or try replacing RY31.


Another thing to check for is whether or not you have about 200vac on the "R" and "S" input terminals. All Fanucs had a multi-tap single phase transformer ahead of the power supply so you could set the power supply's input to 200vac, regardless of your AC line voltage. If your voltage between R and S is not within 5% of 200vac, change the transformer taps until it is.

One last thing: If you still have your old power supply, look to see if there isn't a jumper between a pair of the input terminals (the signals to the ON/OFF buttons). Sometimes a jumper is used to complete the holding circuit. If you replaced a power supply that had the jumper with one that doesn't have a jumper, that would cause your problem also.

Hope this helps.