Lighthouse PLCs, Inc. : Automation Forum
THE PURPOSE OF THIS FORUM IS: AUTOMATION SOLUTIONS. IF YOU ARE A PERSON INVOLVED IN SOME ASPECT OF AUTOMATION, HAVE AN APPLICATION YOU JUST CAN'T QUITE GET A HANDLE ON 
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Hopefully the information presented here will help provide solutions to some of today's automation challenges. Some issues are probably old, some are probably new. Many are products of the economy, the resultant reduction in manpower, exacerbated by aging equipment crippled by decreases in maintenance budgets. The ULTIMATE goal here is that we all become more successful in our careers and chosen professions.
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Mr. Simon Ménard,
Two conditions must be met for the “RUN” light to come on. When the EC first powers up, it goes through an internal diagnostic self-check. The kinds of things this self-check looks for are: if the power supply is delivering the correct voltages, if the CPU and Memory pass tests, and if the program is present, and does not have any syntax errors.
Next, the “STA” terminal need voltage (+24VDC). When STA (Start) sees voltage, the command is sent to go into the “RUN” mode.
My best guess, is either (1) there is a problem with the start circuit (bad switch, loose wire, etc.), or (2) the program has become corrupt. If there is no +24VDC at the STA terminal, then check the wiring and the (RUN?) switch. The “RUN” switch may be located on an operator console, or may even just be a contact on another piece of equipment. If you do not have documentation, you will just have to trace the wiring.
The second scenario is plausible if your system has experienced a voltage spike. The spike could have come from a recent lightning strike, or perhaps a newly installed piece of equipment (like a variable speed drive). A transient voltage spike can wipe a program, destroy the memory, or even damage the processor itself. Without a valid program, the PLC will not go into run mode, even if STA sees voltage.
There is both a DOS, and a Windows based Programming Software package available. Both come with the cable that connects from your laptop COM port (serial) to the 9-pin mini-DIN connector on the face of the EC.
I hope this information has been of some help.
Timothy Davis 
