I have a Fanuc 6M-Model B controller in a Shizuoka Mill that was working well, was not used for a week or so, then when re-started would not boot up. I did some trouble-shooting and found the alarm (red LED) on the Input board lit up, and found that when I disconnected all outputs from the Power Stabilizing Unit (A14B-0067-B002) the alarm went away. I tested further then, using a Fluke multimeter on ohms, I found that the 24v output pins were shorted (zero ohms) to the ground pins. This short turned out to be between the 24v pins that are the left-most two pins on connector CDP, visible in the photo below on the upper right-hand corner of the I/O board, which is a Fanuc A20B-0008-054, and the next two pins to the right, which are both GND.

With the I/O board (A20B-0008-054) completely removed from the system and nothing connected, the short remains as measured at the power connector pins of CDP. Visual inspection shows no anomalies. This I/O circuit board is a multi-layer board, and there are no traces visible from the 24v input pins, and with a zero-ohm short everywhere I test the resistance from ground to either 24v or another ground point my ohm meter reads the same zero ohms and I cannot distinguish which is which.

So my question is simply this, does anyone have or know where I might find a circuit diagram for this A20B-0008-054 board? Or, have any idea how I can find this short without that circuit diagram? Or just know where the 24v is supposed to go? I am completely stumped about how to proceed at this point.

Thanks for your help!

Bill