Direct Logic D3-340

[bgelmore]

I have a few o these controllers and had to replace a CPU. It looks like everything is there in the ladder including the registers for the port setup. I believe the com port 2 that is setup for modbus isn't working. Is there a way to see comm port traffic in DirectSoft? I can't find it. Any other suggestions? There are a few timer values that are written from another PLC to this one that aren't working.

 

[JeffKiper]

Have you called Automation Direct dupport yet? They usually have a good support group. Sorry its been to many years for those old D3-###. I still have the serial interface for them. You may need to talk non ModBus to it. I dont recall what they talked DSN or something like that.

 

[bgelmore]

I have called support. They quickly blamed it on the hardware and said I need to upgrade. I wish it was that simple.

To update, it seems like the CPU is not executing the program on the EEPROM. The spare we had and the other CPU I bought used had no EEPROM so I swapped over the existing chip. I can see the ladder and all of the registers seem to be correct but the program isn't responding to the MODBUS messages or any I/O. Is there a process to format the EEPROM chip? I was able to clear the plc and reload the program but with the same results.

 

[JeffKiper]

It was years ago we had problem connecting to a unit and we replaced the backplane because the capacitors where 20 years old. I called BS but the old timers said to give it a shot and it worked.

 

[Steve Bailey]

Is the D3-340 acting as a Modbus master or slave?
If a slave, with all the things you have tried, could you have changed the Modbus ID of the CPU and consequently the Modbus master is trying to communicate with the wrong device ID.
I second Jeff's suggestion about replacing the rack. The most frequently replaced component in a DL305 (GE Series One, TI305, Simatic 305) was the rack/power supply.
The PORT2 LED should flash when there is traffic on the serial line. If the D3-340 is a Modbus slave you should at least see a brief flash each time the Modbus master sends a command. If the D3-340 is the Modbus master and the LED never flashes, it's pretty safe to conclude that it isn't sending any commands.

 

[bgelmore]

The port light does blink, it is a slave. What makes me stick with the CPU is I can swap a CPU from another identical machine and this machine will work fine with it's existing rack and I/O. This is the machine I uploaded the program and configuration from to download into the replacement CPU. We have four, two are fine and two had the CPU fail within a couple months.