View Full Version : FANUC 11M Amplifier bad, need help!

04-19-2006, 09:34 AM
Dear all!
I have Andy machine with FANUC 11M control.
When I power up the machine, Y axe gives an error:

If I move Y amplifier to X axe, then X axe gives the same error, it seems that amplifier for Y is bad.
Then I moved only PCB part to Y axe but X axe is still giving the same error.
I have 3 amplifiers and any of the combination gives me the result that energetic part of the amplifier is bad.
Here are the codes:
Amplifier: A06B-6058-H005
PCB part has a code: A20B-1003-0090/04A
Energetic part has a code: A20B-1003-0081/01A

My question is: where can I find any instruction manual for FANUC 11M or this kind of amplifier (some maintenance manual)
If this is not possible, I will try to fix the amplifier by replacing components on energetic part. Any hint what could be wrong? Capacitors? Machine is from 1988.
Thank you in advance!

Dan Fritz
04-19-2006, 10:10 AM
You probably have the old 3-phase full wave DC servos, so you'll have a big contactor called the "MCC" on the back of each amplifier. This contactor closes when the servo is ready, and a small set of contacts on the side of the contactor close and send the 24v "VRDY", or Velocity Unit Ready signal back to the CNC.

If you've already eliminated the amplifier board as the cause of the problem, take a look at the MCC contactor when you try to power the control up. If it pulls in and stays in, then you've probably just got a bad pair of the small contacts on the side of the relay.

Here's the "big picture" on what all happens when you power up: When the CNC is turned on and ready, it powers up the servos by outputting a PRDY, or Power Ready signal to each servo board. These signals are +24vdc, and come from small IC reed relays in the CNC. On each amplifier board, there are circuits to check all kinds of things, like tach feedback, current limit, etc.. If all is OK to power up the motor, the amplifier board uses a small solid state relay to turn on the MCC relay. The main contacts in the MCC relay put power to the motor, but the smaller contacts send the VRDY back to the CNC. When the CNC gets the VRDY signal, it activates the velocity command signals to the servo to close the position loop.

Sometimes, the MCC relay kicks in, and then the amplifier board detects something wrong, like an overcurrent condition. It then dumps the MCC relay and VRDY turns off again. In that case, the MCC relay will pull in and dump off immediately. If that happens, look for bad motor brushes or a shorted motor. I doubt that's your problem because the problem would have stayed in the Y axis when you moved the servo. The other possibility is a bad SCR, which would blow fuses whenever the MCC contactor pulls in.

Since you moved the whole amplifier and the problem moved also, that means that the IC reed relay in the CNC is OK. You're right to be looking at the power section of the amplifier.

The amplifier board mounts to the power chassis by plugging on to a bunch of pins. Check to see if any of these pins didn't "push back" when the board was installed. I've seen that happen before.

04-19-2006, 11:10 AM
Thank you very much for the help Dan!!! At friday I will go there and try again and then I will let you know!