I tried the hhp with all I/O modules removed but it dint work.
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You may need to clear PLC memory and download a backup copy of the program. If that is the case, there isn't much more you can do without the programming software. If neither of thos conditions are correct, then the problem is most likely in the CPU. So if it was stopped due to a fault when it powered down, even if you remove the conditions that caused the fault, when you power back up it will remember that it was not running when it powered down and continue in that state when it powers back up.Ĭonversely, if you clear the faults with the I/O modules in place, and it was one of the I/O modules that caused the fault, as soon as you try to put the PLC into the run state, the fault will return. The default CPU behavior is to power up in whatever state it was in when it powered down. I have already tried this.But it didn't work.Run light didn't turn on after removing all 1/o modulesĭid you clear all the faults with the Start90 utility after powering up with all I/O modules removed? Here's why that is important. I have check the voltage by using multimeter.It show 24v. It's also possible that in touching +24 to some of the input terminals you move the wire to terminal 1 and disconnect it. If the negative side of the DC supply is not actually connected to it, then you might possibly see some LEDs light and others not. You should also check the integrity of the connection at terminal 1.
Either that or disconnect the field wire when you touch the +24v to the terminal.
If you can maintain +24v then you can draw the same conclusion as when you touch +24v to an unconnected terminal. On the circuits that don't light the LEDs, check the +24v level with a meter while you touch it to the terminal. If the 24 volt supply can't handle the current draw its voltage will drop and you won't see the LED light up. It's possible that the +24v can backfeed to ground through the field device. If there are field devices connected to the I1 - I16 terminals, it gets a little more complicated. The LEDs are on the field wiring side of the module, so failure to light means no current flow. If it fails to light, then that input point is probably bad.
If there are no connections to any of the I1 - I16 terminals, then touching +24v to them should light the LED. The +24v supply qualifies as a sourcing device. That makes it a sinking input which must be connected to a sourcing device. Since you said you touched +24v to the individual terminals, I'm going to assume you have the negative side of the DC supply connected to terminal 1. The failure of an individual LED to light may or may not indicate a faulty circuit on the MDL645 module.