Electrical Troubleshooting Quiz — October 7, 2025

A custom-built production machine has stopped working. This machine came from another plant, which had ordered it from a machine-builder that went out of business during the Covid shutdowns. As such, there is no vendor tech support to contact.

The in-house maintenance has determined that the three-phase supply to the machine is good, but they have not been able to go much beyond that. They conclude that the failure appears to be electronic in nature. However, nobody in the maintenance department has an electronics background.

You’ve been tasked with figuring out how best to restore this machine to operation. The plant engineer wants it fixed in-house, if at all possible.

Where would you start, and how would you proceed from there?

Answer to Quiz

It’s good to know there is three-phase power to the machine. This means it has its own power supply for the electronics. And the first rule of troubleshooting anything with its own power supply is to check that power supply. In this case, there may be multiple power supply modules. For clarity’s sake, we’ll refer to “the power supply” to cover all of them.

You might be able to verify that the power supply is putting out something by looking for lights on the load side of the power supply. For example, a green Power On indicator. Or you may be able to measure voltage at the input to one of the cards or other devices connected inside the machine. For example, there may be a terminal strip labeled “5V.”

It would also help if you had drawings and instructions. Check your document system and also any cabinet doors in the machine for any drawings and instructions; those should have been provided with the machine. They may have been lost when the machine was transferred. Check with that other plant if you do not have them. If you get those drawings and instructions, identify where the supply fuse or breaker is. Identify any reset buttons.

If the power supply has power in and no power out, and you are sure you’ve got the on/off switch in the correct position, the reset pressed, and any fuses in good condition, you need to replace it. With any luck, it will have turned out that the machine builder used an off the shelf power supply. And that means a replacement is probably available if this one is bad. Maybe not this brand, but one with the same power out and (if used) connectors. Unable to locate one? Then contact a machine builder.

If the power supply has power out, check the load-side connectors to make sure the power is being supplied to the load. See if the machine will operate now. If not, identify exactly where things stop.

Is there a starting permissive that is not satisfied? How about a safety interlock? It may be something as simple as an interlock switch on a cover or door. If you find nothing by going down this path, then the most likely problems are related to the final control elements, such as motors and valves. So start with those and work your way backwards.

If you’re unable to determine what exactly has failed, then contact a machine builder. If you can determine exactly what has failed, replacing it should allow the machine to be put back into service.

Before contacting a machine builder, ask the plant manager how much budget allocation there might be to repair this machine. For a builder to visit onsite means one or two plane fares and one or two nights in a hotel, plus their fee. If those funds cannot be allocated, then you’re done with this project.

If the funds can be allocated, then start looking at machine builders. Go on their website and see if they build machines that are at least a little similar to yours. Prepare a written summary of the problem so that you can start the initial conversation. Supplement this with a video summary. Then contact the builder and get an idea of how much it would cost and when they can do it. Give your findings to the plant manager.