Short Circuit Troubleshooting (Part 2)

We're going to tackle a slightly more complex problem than you saw in the last Short Circuit Troubleshooting lesson. If you haven't completed that lesson yet, you might want to start there. This lesson will build on some of the ideas from that one.
Get ready for a deeper dive into Step 10: Root Causes!
Using the Ten Step Troubleshooting process as a guide, we'll concentrate on finding and fixing the fault as efficiently as possible, without unnecessary risk to equipment or safety.

The Ten Step Troubleshooting Process

This lesson focuses on a particular electrical failure that needs to be found and fixed. Rather than a typical Guess and Check, (sometimes known as Hit Or Miss) method, we will apply the Ten Step Troubleshooting Process, or TSTP.

The TSTP is a logical series of steps that can be adapted to nearly any troubleshooting problem, and followed for an efficient and effective equipment fix.

The Problem

You're a technician at a small gravel extraction company.

Earlier today, before the loader was brought in for repair...

The operator noticed that the hydraulic oil high-temperature warning light was on, and he stopped the machine and went for a coffee break. Afterward, when he restarted his machine, the light was off.

So, he resumed work.

The high temperature light soon came back on, and then went off almost immediately, along with the work lights and the lights in the operator's gauge cluster. The entire circuit seems to be dead.

Experience To The Rescue

This isn't your first day on the job, and you know exactly what these symptoms sound like - a blown fuse. Sure enough, when you check the fuse box, this circuit's fuse has obviously blownâ€¦ violently.

It's easy to replace the fuse, but considering the scorch marks, the fuse almost certainly blew for a reason. It looks like there is a short somewhere in this circuit, and as long as it exists, replacement fuses will just blow as well. You're going to need to find and fix the short circuit - it's troubleshooting time!

Step 1Define The Problem

Electrical problems present in one of three ways.

No Go

E.g. The circuit does not operate. At all.

Both open and short circuits will cause No Go conditions.

Erratic Operation

E.g. The circuit works sometimes, but is not reliable.

Incorrect Value

E.g. The circuit works, but results are wonky. Lights may be dimmer, motors turn faster or slower than they should, sensors display incorrect values.

Our loader problem is a textbook case of "No Go".

Specifically, it's almost certainly a short circuit. This will modify our troubleshooting process slightly.

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