Mitsubishi Fault

Hi ,

I just got called out to our water tower Plc

It is a Mitsubishi Fx2 128

When i looked , the Plc was flashing the first 8 input Led's on the left hand side of the Plc and the first 8 output Led's
Alternating with the prog Led on the right

Is this indicating a specific fault

A few minutes later , It came straight back on

Any advice gratefully received

Thanks in advance

Mike

Hi ,

I'm told by Mitsubishi that the flashing of inputs/outputs alternating with flashing prg light isnt an indicator of a fault that the Plc uses asa warning sign

I think it has to be the power supply

Any Ideas

Thanks - Mike

Hi

It sounds to me that half the bridge rectifier in the power supply of the plc is faulty.

is it 240vac supply to the plc?

You could check the 24vdc output off the plc

I have seen this before, several times and in each case it was overload or dead short on the 24V dc side.
Disconnect the 24Vdv side and see if it stops - then find the short

The only time I have seen this is when a solenoid coil was short on one of the outputs, when the plc powered up the particular solenoid energised dragging down the 24v, as the psu shut down then the overcurrent was lost, hence the 24v came back on.
this caused it to cycle on/off, try disconnecting all the outputs to see if this stops it.

Thanks guys ,

I will check it out

I made a mistake in the original post , only the input lights were flashing in alternating sequence with the program light ( Led )

During the second time it failed , I had voltage checker on me and I had lost 240 volts on the incoming terminals to the Plc

I have , as a precaution , taken a new 240 v supply to the Plc , and the fault has not reappeared , but i need to check all possibilities

Thanks to those responses so far