Siemen S5 110 problems

Hy chaps need someone with Siemens experience here

Today I was called to an old S5 110 ZB/CPU

It is a rack mounted system with 4 input modules and 2 output modules.

I was informed the machine had been powered off for about 2 weeks and when they turned it on the fault red light was on - on the cpu unit.

While it was powered up I turned to run switch to OFF then back to CYCLE and the red light went out. Everything seemed ok for a while then the output modules led’s started chattering causing valves and relays to chatter too.

I checked all the voltages to the outputs modules and the 24V dc in to these was stable but the outputs were jumping around. I then took out each module and cleaned the backpane contacts. Things once again settled down for a while although I never got the machine to run properly.

The problem as it stands is - each time the power is cycled, the red led comes on but goes off when the run switch is cycled.
Oh and the battery was last replaced in 1992.

I have no software to access this plc

Do you think the program is corrupted or maybe the cpu or eeprom is faulty.

I have seen this a couple of times.

The first one was someone replaced a relay (24vdc coil) with a relay (120vac coil).

The second was a shorted relay coil.

You may have an intermitent voltage drop. If you have a scope or meter with recorder it may help run it down.

Good Luck

Thanks for your reply mike. Today, I disconnected everything to this plc except the power and it was still doing it.
I pulled everything out and cleaned and checked and did what you have to do and each time it worked for a short while then got the jitters again.

Its either a bad connection to one of the modules or a faulty connecting ribbon.

But, they have agreed to a new plc putting in so Im not complaining.

take a simple dmm and test the 24 volt dc supply but now switch to ac and test it again maybe faulty diode or capacitor.

In the past, I have seen problems such as you describe when the PLC power supply degraded.

It could well have been that too. But its now going to be a museum piece. The baby was thrown out with the bath water.

There was never any drawings for this machine or anybody that really understood it properly.

They now get furbished with a new plc with full drawings and documentation and maybe a few extra diagnostic helps too.
And I get to sit on my big fat backside for a week or so playing. (for playing read programming)