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Troubleshooting Guide: MicroLogix 1400 PLC not powering up with 120V AC input

Question:

Greetings! We acquired a pre-owned AB MicroLogix 1400 Programmable Logic Controller (PLC) and are facing issues with powering it up using 120V AC input. Despite confirming the presence of the required voltage at the PLC's input terminals, the unit remains unresponsive. Are there any troubleshooting steps or recommendations you can suggest to resolve this issue?

Top Replies

Do you have the product code for your item? Have you tested for 120VAC on the top two terminals of the lower terminal strip (VAC L1 to VAC L2/N)? If you have a solid connection and still no power, your unit may be malfunctioning. Since it's a pre-owned item, do you know its origin?

Inquiring about the catalog number, are you checking for a reading of 120VAC between the top 2 terminals of the bottom terminal strip (VAC L1 to VAC L2/N)? If so, and the connection is secure, it is possible that the unit is non-functional. It was purchased second-hand from an individual and was previously used in a car wash until January of this year. Any suggestions on how to determine if the unit is beyond repair, either through internal inspection or other means, would be appreciated. The catalog number is 1766-L32BWA, and there is a confirmed 120V reading between VAC L1 and VAC N.

I suspect there is a fuse located on one of the circuit boards, possibly the one through which the power is supplied.

Did you receive a refund or were you given a replacement product? You might want to open it up to inspect it. I personally have never had the need to open one before, so unfortunately, I am unable to provide assistance with this.

After removing two boards, I reached the bottom where the power is likely managed. It's unclear whether this is the correct location though. Upon inspection, no signs of significant damage were found.

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Macro Photography: A Detailed Look

The fuse appears to be located directly under the inductor, although it may not be easily removable. It's advisable to verify this during your inspection. Remember to exercise caution as there are potential hazards such as electric shocks in the area.

MikeyN pointed out that the fuse is located just below the inductor. While it may not be easily removable, it is worth checking. It is important to exercise caution as there are potential hazards present. Is there a way to test the fuse for continuity? It would be convenient if it were a linear fuse that could be checked by measuring continuity between the inlet and outlet. Is it possible to replace the fuse if needed?

After examining the board and discovering no continuity between the solder points, I suspect a faulty fuse is the issue. Considering the potential for a short circuit in the programmable logic controller (PLC), is it worth the effort to desolder and replace the fuse? I am concerned that replacing the fuse may just lead to another blown fuse due to a hidden short circuit.

lukethorwart inquired about testing a fuse and whether it is possible to replace it with a linear fuse that can be checked for continuity between the inlet and outlet. To test the fuse, you can jump it out, power it up, and observe the results. It is important to find the rating of the fuse and use one with the same rating in your power wire set-up. This approach may not worsen the situation.

When faced with a power issue in your setup, saultgeorge suggests trying to jump-start it and see if that solves the problem. Check the fuse rating and make sure to replace it with one of the same rating in your power wire setup. It's worth a try to improve the situation, right? If you're unsure how to jump-start it, the solution may lie in soldering to two points on the back of the board.

When connecting the solder wire from one pin to another, it is important to consider the potential risks of powering it up. Failure to do so could result in damage to the device. Instead of risking damage, it may be more advisable to return the item for a replacement.

A suggestion from geniusintraining is to carefully solder wire from one pin to another on a used controller to fix it. However, it's important to be cautious as powering it up could potentially cause damage. It might be a better idea to return it to the seller and opt for a replacement instead. Thank you for your advice and input.

It is not advisable to bypass the fuse without understanding the root cause of the issue. It is recommended to follow GIT's guidance and seek a replacement for the blown fuse. If you are determined to troubleshoot the issue, consider soldering in a new fuse or connecting wires to the fuse spots. Attach the wires to a glass fuse holder for testing purposes.

If you're looking to replace the fuses, you can find affordable options in stock on Mouser. Alternatively, you can search for the part number online to easily locate the fuses.

I successfully revived a malfunctioning ML (potentially a 1400 or 1500 model) by troubleshooting and fixing its internal circuit board. The board featured 6 connections for incoming power - 2 each for hot, neutral, and ground. Upon inspection, I discovered traces running between these connections and the pins on the lower board with the power supply. The multi-layer circuit board revealed hidden traces sandwiched between its layers, with one visible hot trace on top and a ground trace on the bottom. After identifying a fuzzy smoke inside the board's neutral trace, I suspected a manufacturing issue from a possible Rockwell Detroit circuit board supplier. To resolve the problem, I soldered a wire from the incoming neutral terminals to the back of the board, resulting in a fully functional PLC. This repair only cost me 6 cents and an hour of my time, showcasing the power of DIY troubleshooting for electronic devices.

Frequently Asked Questions (FAQ)

FAQ: FAQs:

Answer: 1. Q: Why is my MicroLogix 1400 PLC not powering up with 120V AC input despite voltage confirmation? There could be various reasons for this issue, such as a faulty power supply, internal component damage, or incorrect wiring connections. 2. Q: What are some initial troubleshooting steps I can take to address the power-up problem with my MicroLogix 1400 PLC? You can start by checking the power supply integrity, verifying the wiring connections, ensuring proper grounding, and inspecting for any visible damage to the PLC unit.

FAQ: 3. Are there specific indicators or LED lights on the MicroLogix 1400 PLC that can help diagnose power-related issues?

Answer: Yes, the MicroLogix 1400 PLC typically has status indicators or LED lights that can provide insights into power supply status, communication errors, and general system health.

FAQ: 4. Should I consider resetting the MicroLogix 1400 PLC as part of troubleshooting the power-up problem?

Answer: Resetting the PLC can be a valid step in troubleshooting, but it should be done cautiously and following proper procedures to avoid data loss or further complications.

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