Why Is My Scale Not Working? A Simple Troubleshooting Guide

If your industrial scale has stopped working, don't immediately assume the load cell has failed.

Many weighing problems are caused by a loss of excitation voltage, damaged wiring, failed load cells, or a faulty indicator.

The troubleshooting steps below follow the same process our technicians use to isolate the problem before replacing expensive components.

Step 1: Is the Indicator Turned On?

Before testing anything else, verify the indicator has power.

Check:

• Display is illuminated

• Power cord is connected

• Circuit breaker hasn't tripped

• Power supply is functioning

• No blown fuses

If the indicator won't power on, resolve the power issue before moving on.

Step 2: Check for Excitation Voltage

Once the indicator is powered on, measure the excitation voltage.

Measure between:

• +EXC

• -EXC

Most indicators provide between 5 and 15 VDC.

If Excitation Voltage Is Present

The indicator is supplying power to the load cells.

Proceed to Step 3.

If There Is No Excitation Voltage

Disconnect the load cell(s) from the indicator and measure the excitation voltage again.

Excitation Returns

If the excitation voltage returns after disconnecting the load cells, the load cell circuit is pulling the excitation voltage down.

This usually indicates one or more failed load cells or a shorted load cell cable.

Still No Excitation Voltage

If there is still no excitation voltage with all load cells disconnected, the indicator has likely failed and should be repaired or replaced.

Step 3: Is Your Scale Using One Load Cell or Multiple Load Cells?

This changes the troubleshooting process.

Single Load Cell

Inspect the cable for:

• Cuts

• Pinched insulation

• Moisture

• Rodent damage

• Broken strain relief

If the cable appears normal, proceed to load cell testing.

Multiple Load Cells

If your system uses multiple load cells, each load cell should be tested individually.

Disconnect each load cell from the junction box one at a time.

This helps isolate which load cell is causing the problem.

Step 4: Check the Millivolt Output

Using a digital multimeter:

Measure between:

• +SIG

• -SIG

A properly functioning installed load cell will typically read between 0 and 5 mV, depending on the system's dead load.

Warning Signs

• Greater than 10 mV

• Negative millivolt reading

• Unstable output

• Output that does not change when weight is applied

These conditions often indicate a failed or damaged load cell.

Step 5: Isolate the Problem Load Cell

If multiple load cells are connected:

Disconnect one load cell.

Does the indicator begin operating normally?

Yes

The disconnected load cell is likely defective.

Reconnect the remaining load cells and continue testing to verify there are no additional failures.

No

Reconnect that load cell and disconnect the next one.

Repeat the process until the faulty load cell(s) have been identified.

Remember that more than one load cell can fail, especially after events such as lightning strikes, flooding, or severe overloads.

Step 6: Confirm the Diagnosis

Once the suspect load cell has been identified:

• Compare resistance readings to the manufacturer's datasheet.

• Inspect the cable and connector.

• Verify the load cell is not mechanically damaged.

• Confirm there is no binding or obstruction affecting the scale.

Replacing components before completing these checks can lead to unnecessary repairs.

Need Help Troubleshooting Your Scale?

If you've completed these tests and are still unsure what's causing the problem, our technicians can help.

Whether you're troubleshooting a truck scale, floor scale, tank scale, livestock scale, or other industrial weighing system, we can help determine whether the problem is the indicator, load cell, junction box, wiring, or another component.

Contact American Scale Supply for expert troubleshooting assistance.