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LB15 Lathe with Fanuc spindle drive problem seeking help


May 12, 2024
Hi Guys,
I'm looking for some help. Can anyone suggest a Fanuc tech, I'm based in Melbourne Australia 3913.

I have an old Okuma LB15 L-G 5000 control, with a Fanuc spindle / servo drive unit ( FANUC AC SPINDLE SERVO UNIT A06B-6055-H108). When I try and start the spindle the spindle jerks then quickly throws an SDU alarm.

I actually have two of these drives (one spare) when I swap each of the top boards around I get Fanuc LED Alarm 2 on one board and LED alarm 12 on the other. Both spindle drives show the same alarms depending on what top board is installed.

My lathe is based at the Tyabb airport VIC 3913. Australia

My number us 03 5977 3805 email: [email protected]

Regards, Paul
Hello Paul

I have the near identical machine and the original spindle drive just breathed its last.
It went to Worldwide Industrial Solutions for a rebuilding.
I believe that Tennessee Industrial also has these rebuilt and in stock for a core exchange.
The electronics are 40 years old and getting creaky. Mine had no issues at all - until it did.
I'm told the top board with AL 12 has some serious issues and should not be used due to is creating an over current state.

However top board with AL 2 is apparently repairable. I have the Fanuc manual and can see various tests that can be done in relation to alarm 2. So far I have check all the fuses and they are all ok.

There is also an adjustment able to be made on pots RV18 and RV19 which sets the speed feedback duty signal, supposed to be set at 50%.

I did read online a chap that was having similar issues to mine and the problem was the speed sensor mounted to the AC spindle motor. An oscilloscope would confirm that I guess. Never used one!Fanuc top boards May 2024.jpg
Hi All,

Today, via pots RV19 and RV18 to set the voltages to 2.5 VDC each, measuring at check points CH7 and 0V then CH8 and 0V. Unfortunately the spindle still gives issues, continuing to throw Fanuc AL 2,
The video link below shows where I'm at. Any help would be gladly accepted.

Are you sure the motor UVW wires are correct? It seems that the spindle first goes in 1 direction and then switches to the other side. I am happy to see you log your problem, which is really usefull for the online knowledge base :)