Help with Fanuc AL-12 alarm

[g***@yahoo.com]

I got an AL-12 alarm on my lathe with a 18-T control. Does anyone have
a copy of the Fanuc document 4240-Troubleshooting AL-12 on S and P
Series Spindle Amplifiers. Includes info on testing transistor
modules.

It is no longer available on there website and I need to know where to
start checking for the problem. Any help would be appreciated.
Thanks,
Greg

[Tero Kaarlela]

Hi,

We had same alarm earlier this year on our Fanuc spindle drive. Problem
was that machine gave A-12 when accelerating or decelerating spindle.
Reason was broken power transistor(IGBT module)


Tero

Post by g***@yahoo.com
I got an AL-12 alarm on my lathe with a 18-T control. Does anyone have
a copy of the Fanuc document 4240-Troubleshooting AL-12 on S and P
Series Spindle Amplifiers. Includes info on testing transistor
modules.
It is no longer available on there website and I need to know where to
start checking for the problem. Any help would be appreciated.
Thanks,
Greg

[Warren]

Greg,
Yes, AL-12 is the most dreaded alarm on a Fanuc Spindle drive.
Unfortunately, this alarm usually indicates not only a bad IGBT (power
transistor module), but also a bad section on the driver board.
Sometimes in the early stages of this board going bad, you can still
run the drive for a few hours or minutes. When our customers want to
just change the bad IGBT and not the board, we usually either 1) have
them send the whole drive to someone else to get fixed, 2) have them
call Fanuc to come fix it on site, or 3) ask them to accept the risk
of buying more modules if the fix doesn't last. It is a grim
situation. The good news is that these are good drives and you
shouldn't have to face this very often. You can find the bad module in
just a few minutes with an ohmmeter. Just disconnect the motor and
look for shorts between each of the three phase terminals to the motor
and the DC buss wires coming into the module(s). Make sure the
disconnect is OFF AND that the DC has bled off of the capacitors. We
received one of these drives once via UPS and there was enough energy
in the capacitor to melt a screwdriver. - Warren