90-30 Troubleshooting & Repair (brand new PLC technician)

[KingLukeXVI]

Hello! My name is Luke and I started training about a month ago at a company to repair and remanufacture PLCs. I've done a lot of training and learning about circuits and how they operate and function but not a lot on how to actually repair these devices. I've been given 10 IC693MDL740 units to troubleshoot and repair, however beyond testing it in Proficy Machine Edition and testing the outputs with 24V DC, I have no clue what to be checking on the board and what to look for. Any help is greatly appreciated, whether its direct help or if I'm pushed towards some information. Thanks for reading & I hope to learn a lot from everyone!

 

[geniusintraining]

....however beyond testing it in Proficy Machine Edition and testing the outputs with 24V DC, I have no clue what to be checking on the board and what to look for....

What else are you looking for? I would get a rack, power supply and CPU and wire up the outputs, make a test program to energize the outputs on a timer, if they all turn on and off under a load they are working in my opinion

 

[Steve Bailey]

I just pulled a circuit board out of a module. The solid state devices look to be pretty easy to replace once you identify which circuit(s) have failed. But, they aren't very expensive modules. So you'd better be able to diagnose and repair quickly if your company plans to make any money doing it.

 

[parky]

Many years ago, I used to repair many electronic systems, Intermittent or heat faults are the most difficult, these often require extensive testing before & after repair, so sometimes are not worth repairing due to cost.
I/O cards are an example, one way of testing is to use an input & an output wired to each other, write a small program so the outputs scan one after the other, the program is written to detect a non change from output to input and generate an alarm.
Common faults that are pretty easy to diagnose are:
PSU's failed low value surge resistor in power line, failed Switch mode power transistor, failed rectifier diodes or bridge, HF transformer for SMPS open circuit, failed capacitors or dry joints especially on large heavy components.
I/O cards bad joints particulary on connectors or larger components, failed opto isolators, output relays or transistors.
Racks etc. most often dry joints on connectors.