This module will walk through the steps of efficient troubleshooting to find and fix an open circuit fault.
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.
As a technician for a small gravel extraction company, you're pretty busy keeping the fleet of machinery running, and today is no exception. The operator of a front end loader has complained that the forward-facing headlamps on top of the loader cab are not illuminating when the light switch is toggled. All of the other headlights and marker lights come on, and the gauge cluster illuminates too.
The loader is not road-legal without the headlamps, and it is dangerous for the operator to work without sufficient light. It has been brought into your shop and you have locked out and tagged out the machine. It's troubleshooting time!
Electrical problems present in one of three ways.
Our loader problem seems like a clear-cut case of a "No Go" problem.
Before visiting the loader, you stop by the bookshelf and grab the manual. A few page flips get you to the wiring diagram for the headlamps, and you take a moment to review the circuit.
The manufacturer has provided a schematic with the manual, so you are ready to go.
Touch each call-out to quickly review some circuit basics.
These lamps will not light. What could the problem be?
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.
There's nothing in the shop records about an issue with the lights. This is likely the first time this problem has come up.
In Step 1, you determined that this is most likely a "no go" problem. Now that you've consulted the schematic, make a list of ALL of the places where a failure could cause a "no go" fault.
Don't worry about limiting it to just the places where it could cause this exact failure - think about ANY possible failure leading to "no go" at this point. The goal at this stage is to create a large list that does not overlook any possibilities.
Touch the call-outs to examine each component and determine whether it should be on the list.
As you consider each component, ask yourself these questions:
Store power for the circuit
What Can Go Wrong With It? | Could This Cause a "No Go" Fault? |
---|---|
Battery depleted | Yes |
Short circuit across posts | Yes |
Posts corroded | Yes |
Connects/disconnects the power source and the circuit
What Can Go Wrong With It? | Could This Cause a "No Go" Fault? |
---|---|
Fails Open | Yes |
Fails Closed | No |
Protects circuit components from excessive current
What Can Go Wrong With It? | Could This Cause a "No Go" Fault? |
---|---|
Fails Open | Yes |
Fails to Open | No |
Connects/disconnects the power source and the circuit
What Can Go Wrong With It? | Could This Cause a "No Go" Fault? |
---|---|
Fails Open | Yes |
Fails Closed | No |
Connects components in the circuit by providing a path for electricity
What Can Go Wrong With It? | Could This Cause a "No Go" Fault? |
---|---|
Wiggle loose/breaks | Yes |
Insulation worn away, shorting to frame, depleting battery | Yes |
Closes when the sensor heats beyond 85°C/185°F
What Can Go Wrong With It? | Could This Cause a "No Go" Fault? |
---|---|
Fails Open | Yes |
Fails Closed | No |
Set Too High | Yes |
Set Too Low | No |
Illuminates
What Can Go Wrong With It? | Could This Cause a "No Go" Fault? |
---|---|
Burned-out filament | Yes |
Shifts the valve
What Can Go Wrong With It? | Could This Cause a "No Go" Fault? |
---|---|
Solenoid coil fails (does not shift valve) | Yes |
Valve spool sticks open | No |
Valve spool sticks closed | Yes |
Valve spool travels incompletely | No |
Energizes the relays
What Can Go Wrong With It? | Could This Cause a "No Go" Fault? |
---|---|
Fails Open | Yes |
Fails Closed | No |
Connects lamps to the voltage source
What Can Go Wrong With It? | Could This Cause a "No Go" Fault? |
---|---|
Coil failure - will not operate | Yes |
Contacts burned/oxidized | Yes |
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