GE Fanuc 90-30 - PWR led blinking

[Henry-operator]

Hi,

Have very basic knowledge of PLC's. Wondering if someone can point me in the right direction.

Our assembly equipment is being run off of this PLC. One day the machine just turned off. I go look at the plc and the power supply is blinking "PWR".
I have checked the connections going into it and it's receiving the 120. I even hooked up a separate 120v power source to rule out bad input voltage.

The power supply is IC693PWR321T and the base plate/cpu is IC693CPU323T.

One thing I noticed is that I took the power supply off for a minute from the base (it says on the base plate that if left out the power supply for more than an hour then the memory might be lost, so I was careful with this to do it quickly) and when the power supply is disconnected from the back plate then it shows a solid PWR led. But when I reseat the power supply back to the back plate, the PWR led blinks as in the video.

Video: https://youtube.com/shorts/Azn2P4UrJa4

 

[Steve Bailey]

It sounds like the PLC is failing its self-test at power-on. You've probably already lost the program. One quick thing to try is to remove all of the I/O modules and reapply power to see if it can successfully power up. If that works, reinstall the I/O modules one at a time until you fin d the one that's dragging it down.
Otherwise, there's a strong possibility the CPU is toast. You could try leaving it disconnected from the power supply overnight. In the morning when you reapply power, tap your heels together three times and whisper, "there's no place like home".

 

[plvlce]

I don't have any experience with Fanuc PLCs, but I did once have a generic 24V power supply that failed with almost identical symptoms of blinking output power just like that. 120 input, blinking 24V output even with load wiring disconnected. Identical power supply right next to it fed from the same 120 source showed no problems...

The fact that you can get a solid PWR light suggests that the power supply itself *might* not be the problem. Many modern power supplies will shut off if they detect a short-circuit or similar problem. I wonder if there is such a problem that only presents itself partway through the power-up process. In other words, it starts to power up, detects a problem and shuts off, but this causes the problem to go away, which is detected so it starts to power up again...

I would try disconnecting the 24V output wiring and applying power, and if that does not cause a change then removing all other modules to see if one of them is causing the problem.

I certainly wouldn't count on the program still being there at this point though.

 

[Henry-operator]

It sounds like the PLC is failing its self-test at power-on. You've probably already lost the program. One quick thing to try is to remove all of the I/O modules and reapply power to see if it can successfully power up. If that works, reinstall the I/O modules one at a time until you fin d the one that's dragging it down.
Otherwise, there's a strong possibility the CPU is toast. You could try leaving it disconnected from the power supply overnight. In the morning when you reapply power, tap your heels together three times and whisper, "there's no place like home".

I removed all of the I/O modules and it's still blinking. It's only when I remove the power supply module off the back panel (but still connected to power at the input) that the PWR led becomes solid and doesn't blink

 

[Steve Bailey]

When the power supply is in place in the baseplate, it is connected to the CPU (which is also in the baseplate), and thus reflects a lack of a signal necessary to continue the power-up sequence.
BTW, the 90-30 hardware is not rated for powered insertion. You may get away with it, but you're playing with fire.

 

[Henry-operator]

I don't have any experience with Fanuc PLCs, but I did once have a generic 24V power supply that failed with almost identical symptoms of blinking output power just like that. 120 input, blinking 24V output even with load wiring disconnected. Identical power supply right next to it fed from the same 120 source showed no problems...

The fact that you can get a solid PWR light suggests that the power supply itself *might* not be the problem. Many modern power supplies will shut off if they detect a short-circuit or similar problem. I wonder if there is such a problem that only presents itself partway through the power-up process. In other words, it starts to power up, detects a problem and shuts off, but this causes the problem to go away, which is detected so it starts to power up again...

I would try disconnecting the 24V output wiring and applying power, and if that does not cause a change then removing all other modules to see if one of them is causing the problem.

I certainly wouldn't count on the program still being there at this point though.

Thank you! Ok. I removed the 24v output and everything lit up. So this seems to be the culprit.

 

[Steve Bailey]

Great! Now all you need to do is see what is dragging down the 24 VDC. The power supply is rated for a total load of 30 watts and the 24 VDC is good for 800 mA.
The capacity of the power supply deteriorates over time. I once visited a site that was experiencing intermittent shutdowns. I tracked it down to the power supply when I shut it down by plugging in the RS232/RS485 converter which draws power from the serial port.

 

[plvlce]

Thank you! Ok. I removed the 24v output and everything lit up. So this seems to be the culprit.

Wonderful. There is a good chance that something wired to it is shorted or otherwise failed, just a matter if singling out the culprit.

As Steve notes, this does not *entirely* rule out the possibility that the power supply is the problem, having become overloaded due to a decrease in capacity as it aged.

imo chances are better that the power supply is ok and some other device is the issue though.