[tsalpha]

Thanks in advance for any replies.
I have a 1981 Kitamura with a Fanuc 6MB. The control will no longer turn off, or back on properly after it is shut down. There is a RED led lit on the main PCB, labeled (WDALM). Any clue as to the source of the problem. Did a quick scan through the Jap/English manual without finding any reference to WDALM or the indication of the red led.
Thanks again,
Tom

[Dan Fritz]

WDALM means "Watch Dog Alarm". The alarm is there as a safety backup to prevent the servos from running away if the CNCs microprocessor should get hung up somewhere. The alarm is triggered by a simple little timer circuit that goes off if the microprocessor DOESN'T write to a particular I/O address periodically. Basically, the processor has to say "Hello - I'm here" every 100 milliseconds or so to prevent the timer from going off. If there's a serious malfunction in the microprocessor, or if the processor gets hung up on a bad instruction, the timer goes off and shuts things down gracefully.

About the only thing that you can do is be sure that all the EPROM chips are plugged securely into their sockets on the ROM board, and that there aren't any boards plugged into the wrong socket anywhere. The EPROMs can work loose from many hot/cold cycles over the years, so you may want to just remove the ROM board and push on all the EPROMs to be sure they're seated. Also look for any "bent under" pins on the EPROMs. A pin that's bent under can frequently be seen with a magnifying glass without removing the chip from the socket. You can spot the EPROMs by the fact that they have the little glass window on the top, which is usually covered by tape to prevent erasure. They're typically erased with a UV light, and you can reprogram them if necessary. On the 6-A series controls, there were several rows of EPROMs on the main (master) PCB. On the B models, there's a separate "daughter" board called the ROM board that's plugged into the master PCB.

If it's not something simple like a loose EPROM, then you'll probably need a new or refurbished master PCB.

One only other thing that can cause this is an option parameter that got set even though the EPROMs for that option aren't there. That causes the CPU to try to access an empty EPROM socket, locking up the microprocessor. The Fanuc 6 is pretty much immune to that kind of malfunction because it doesn't let you enter option parameters if the EPROMs aren't there. The only way that could happen is if someone swaps out the bubble memory board with one that has the parameter bit for the uninstalled option. Anyone been swapping boards lately?

Good luck with this one.

[tsalpha]

Thanks Dan,
I'll check the EPROMs tomorrow morning, although nothing has been added or removed from the main board lately. Hopefully heat has loosened something, I'm not counting on it. Just figures, I signed papers on a new Bridgeport/Hardinge VMC760XP3 yestarday, the ole' gal only needed to keep going for 2 more weeks.

[tsalpha]

Nothing loose, control came back on after tapping relay on the input unit board. Red alarm did not turn on untill the control power on or off buttoms are pushed. This is when a relay click was heard and the red led would turn on. Could this relay be the cause of the problem? Machine runs fine now.

[Dan Fritz]

On the Input Unit board, you should just have a pair of relays marked RY1 and "ALM" and an "ALM" LED (this is not the same as the Watchdog CPU alarm). When you press the ON button, RY1 should come on and hold itslef on through a pair of its own contacts. When you press the OFF button, the circuit is broken and the control power supply shuts off.

The ALM light will come on if the control's power supply detects a problem of any kind. For example, if you have a shorted limit switch on the machine, the +24v might get shorted, causing the power supply to detect an overcurrent condition. The power supply will then trigger this alarm circuit and tell the Input unit to shut down (as if you pressed the "OFF" button). When the ALM LED is lit, you must shut off the CNCs main power, then turn it back on to reset the alarm, then you can turn the control back on.

Any short-circuit anywhere on the machine can cause this, but the most likely causes are limit switches that are exposed to coolant, chips & oil, like the axis limit switches, tool changer switches, etc. Also check any cables that flex as the axes move. If you can flex a cable and trigger the alarm, that could be a wire thats' shorted inside the cable.