LK-401 communications error

[jaze3927 1]

I am seeing a communication error on a series of (7) C200H PLC units connected by LK-401 link units, AL-001 link adapters. Setup: - all 7 link units show flashing red error indicator. - Link 0 position and first 4 PLC's (first 4 in terms of physical wiring, node addresses are 2-5) show "Run", "This" and "Link 0" indicators lit, "other" indicator out. - Last two PLC's (last in terms of physical wiring, node addresses 1 and 6 respectively) cycle through various configurations of indicators shown. - Last two PLC's not transmitting alarms, etc. - SW1/SW2 - 0/[node number] - SW3/SW4 - 3/2 - SW5/SW6 - to the right / to the right - SW7 - pins 1-2, 4-8 OFF, pin 3 ON Troubleshooting so far: - I check the SR 250 areas and they show an error flag for the last two units when looking from another node. When looking from one of those nodes, shows error flag for the last two units plus Link 0 unit. - I've tried swapping LK401 units out on the last two units with known good and no change. - I did resistance check looping pin 5->9 from Link 0 position down to each node and found good readings (5, 6, 7, 8, 9, 11 ohms respectively) Maybe a grounding problem? Not sure what else to check. Any ideas would be helpful!!! Regards, - Evan

[BobB 58]

If you have RT201/202 units down the line it is probably there - check the lights on them. They have been discontinued by the way - old product. I am just looking at replacing several I/O systems at the moment due to the failure of some RT202 units.

[jaze3927 1]

Bob - Thanks for your reply. Unfortunately no RT 201/202 cards in the system. Regards, - Evan

[BobB 58]

Yes, could be grounding, faulty terminating resistor possibly. Are there separate power supplies to the units or does the power supply come from one place? If separate power supplies, could be earth potential differences in different places. I normally use 24VDC and not AC at all - the DC comes from the same place usually. Hope this helps. Edited 7 Nov 2012 by BobB

[jaze3927 1]

After being able to do some more troubleshooting, I've found that the problem is following specific nodes numbers, not the hardware. Now the problem has expanded to nodes 4-6 (of 0-6) (regardless of physical position). I'm now seeing only the run indicator solid green and flashing red error indicator. Any ideas? Thanks!