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.
You're a technician at a small gravel extraction company.
A loader with seemingly dead circuits has come in.
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.
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 blown… 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!
Electrical problems present in one of three ways.
E.g. The circuit does not operate. At all.
Both open and short circuits will cause No Go conditions.
E.g. The circuit works sometimes, but is not reliable.
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.
Before doing anything else, head to the bookshelf and grab the manual & schematics for this loader.
If you have a schematic that is up to date, and verified for accuracy, congratulations! You are miles ahead in troubleshooting this problem. An accurate and trustworthy schematic is the key to an electrical system; it can provide:
Touch each call-out to quickly review some circuit basics.
The electrical side of this machine is powered by a 24VDC battery bank.
The circuit can be locked out using this disconnect.
A simple "blade" style automotive fuse provides circuit protection.
When the ignition is off, key systems on the machine do not run.
This N.O. switch closes when the oil reaches 85C (185F) degrees.
Illuminates when the temperature switch closes, indicating the oil is overheated.
When energized, this solenoid operated hydraulic valve shifts to connect the fan motor to a supply of hydraulic fluid flow.
The fan motor requires flow of fluid in order to spin.
These lamps are mounted on top of the loader cab for nighttime work illumination.
This N.O. toggle switch powers the coils in the lighting relays
These relays connect the high current work lamps to a power source.
These bulbs are backlights that illuminate various gauges on the operator's console.
Review the shop records. Has this loader or others like it been in for repairs recently? Look for evidence of a recurring problem, or a maintenance-induced problem.
It looks like something was up with the same electrical circuit a few months ago; the fuse in this circuit was replaced 4 times in just a few weeks. There's no sign of problems since, though.
Think of the ways each component could fail. Could that cause a no-go fault?
In this step, try to list failures that could cause any no-go fault, regardless of how likely it may be.
This is a list that you will only have to create once.
In fact, you can create this list before there is a malfunction, along with similar master lists for erratic motion and incorrect value faults. Once you have it, these lists become extra tools in your troubleshooting kit.
As you consider each component, ask yourself these questions:
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