kolyur
Lifetime Supporting Member + Moderator
I'm hoping someone can help me diagnose a fault on a Micrologix 1500. I have a 1764-28BXB base (24vdc power) with an LRP processor. When power is applied, the PLC faults immediately. RSLogix says the error is D79h, "Expansion I/O module 13 generated an error". Well, slot 13 is a 1769-IF4 analog input module. It's the last card in the rack and there is an endcap in place. There is also a 1769-PB2 power supply about halfway down the rack, so the power supply distance rating of the analog card should not be exceeded. I looked in the IOS function file to see the specific fault code for slot 13, but it just reads "0" (no faults).
The funny thing is, if I clear the fault in RSLogix, the system will work fine until the next power cycle. All of the analog channels work properly. So, it seems like there is some kind of momentary condition at power-up that is causing the fault. I've tried setting the "Ignore Configuration Error" checkbox in the slot 13 advanced configuration (no effect) as well as removing all wiring connections from the card (no effect), and powering the analog card from bus power vs external power (no effect).
I'd appreciate any suggestions.
The funny thing is, if I clear the fault in RSLogix, the system will work fine until the next power cycle. All of the analog channels work properly. So, it seems like there is some kind of momentary condition at power-up that is causing the fault. I've tried setting the "Ignore Configuration Error" checkbox in the slot 13 advanced configuration (no effect) as well as removing all wiring connections from the card (no effect), and powering the analog card from bus power vs external power (no effect).
I'd appreciate any suggestions.
