How to Test a USB-C Cable with FNIRSI FNB58BT USB Tester Malaysia
How to Test a USB-C Cable with FNIRSI FNB58BT USB Tester Malaysia
Not all USB-C cables perform the same.
Two cables may look almost identical, but one may support fast charging correctly while another results in slow charging, lower power or unstable performance.
When troubleshooting USB-C charging problems, technicians often check the charger first. However, the USB-C cable should also be tested.
A multifunction USB tester such as the FNIRSI FNB58BT can help technicians investigate cable performance and charging behaviour.
Why Should You Test a USB-C Cable?
USB-C is only the connector type.
It does not automatically mean that every USB-C cable has the same electrical or charging capabilities.
Depending on the cable and application, differences may exist in:
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Current capability
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Power capability
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Internal resistance
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Voltage drop
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E-Marker information
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Charging protocol compatibility
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Data capability
This means changing the cable can sometimes completely change charging performance.
Example: Same Charger, Different Cable
Suppose you have a USB-C charger and two cables.
With Cable A, the device charges normally.
With Cable B, the same device charges much more slowly.
Because the charger and device have not changed, the cable becomes one of the first components to investigate.
The FNB58BT allows you to observe the electrical behaviour during each test.
Step 1: Establish a Reference
Before comparing cables, establish a consistent test setup.
Use the same:
Charger
Device or electronic load
USB tester
Battery condition where possible
Only change the cable.
This is important because changing both the charger and cable at the same time makes the results difficult to interpret.
Step 2: Check Voltage
Start by observing the voltage.
If the charging system has successfully negotiated a higher-voltage charging mode, the displayed voltage may be higher than the traditional USB 5V level.
However, the expected voltage depends on the charger, device and charging protocol.
Do not assume that every fast-charging system must operate at the same voltage.
The measurement should be compared against the expected behaviour of the equipment being tested.
Step 3: Check Current
Next, observe the charging current.
If one cable consistently results in significantly lower current under comparable conditions, further investigation may be required.
For example:
Cable A: Higher and stable current
Cable B: Lower or unstable current
This does not automatically prove that Cable B is defective, but it provides useful evidence for troubleshooting.
Step 4: Compare Actual Power
Power can be approximated using:
Power (W) = Voltage (V) × Current (A)
For example:
9V × 2A ≈ 18W
If another cable under similar conditions produces:
9V × 1A ≈ 9W
there is a significant difference in charging performance.
The technician can then investigate whether the cable is responsible for the limitation.
Step 5: Check for Voltage Drop
Cable resistance can become important when higher current passes through a USB cable.
A poor-quality, damaged or unsuitable cable may contribute to excessive voltage drop.
This can affect charging performance and stability.
Cable comparison should therefore not focus only on whether the device is charging.
The question should be:
How well is the cable delivering power under load?
Step 6: Check E-Marker Information
Some USB-C cables include an E-Marker, particularly where the cable needs to communicate its capabilities to connected equipment.
The FNIRSI FNB58BT provides functionality that can be useful for reading compatible E-Marker information.
This can help when identifying or comparing USB-C cables used for higher-power applications.
It is especially useful when several cables look physically similar and their original labels or packaging are no longer available.
What Is an E-Marker?
An E-Marker, or electronically marked cable, contains a chip that provides information about the cable to compatible USB-C equipment.
For technicians, this provides another source of information when investigating whether a particular cable is suitable for an application.
However, E-Marker information should be considered together with actual electrical testing.
A cable should not be judged from only one parameter.
Can You Identify a 100W or 240W Cable by Appearance?
Not reliably.
USB-C connectors can look very similar externally.
A thicker cable may appear more capable, but physical appearance alone is not a reliable technical test.
When cable capability matters, check the manufacturer's specification and use suitable test equipment.
This is particularly important for applications involving:
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Laptop charging
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High-power USB-C adapters
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USB-C docking equipment
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Power banks
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Portable electronics
Why Does a Cheap USB-C Cable Charge Slowly?
There are several possible reasons.
The cable may have:
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Higher internal resistance
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Insufficient current capability
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Poor connector contact
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Damage from repeated bending
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Inappropriate construction for the application
But the cable is not always responsible.
Slow charging can also be caused by the charger, device, protocol negotiation, battery temperature or battery management system.
This is why measurement is better than guessing.
How to Compare Two USB-C Cables
A simple comparison procedure is:
1. Connect Cable A
Record voltage, current and power.
2. Allow the reading to stabilise
Avoid comparing readings taken under completely different device conditions.
3. Replace only the cable
Keep the charger and device unchanged.
4. Connect Cable B
Record the same parameters.
5. Compare the results
Look for meaningful differences in voltage, current, power and stability.
This type of A/B comparison can quickly reveal whether changing the cable affects charging performance.
Can FNB58BT Test a Broken USB-C Cable?
It can help diagnose certain charging-related cable problems, but it should not be treated as a universal cable fault detector.
For example, measurement behaviour may help identify:
Abnormal voltage drop
Reduced charging current
Unstable power delivery
Unexpected charging behaviour
For complete electrical continuity or individual conductor testing, additional test equipment may still be required depending on the fault.
USB Cable Testing for Repair Shops
The FNB58BT can be particularly useful for mobile phone and electronics repair businesses.
Imagine a customer saying:
“My original charger is fast, but now my phone charges very slowly.”
Instead of immediately selling a new charger, the technician can test systematically:
Original charger + original cable
Original charger + known-good cable
Known-good charger + original cable
Known-good charger + known-good cable
This process helps narrow down whether the problem is more likely related to the charger, cable or device.
FNB58BT for USB-C Troubleshooting
The value of the FNIRSI FNB58BT is not simply that it displays voltage and current.
Its wider USB testing functions make it suitable for investigating modern charging systems involving:
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USB-C
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Fast charging
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USB Power Delivery
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PPS
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USB cables
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E-Marker information
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Chargers
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Power banks
For technicians who regularly troubleshoot charging problems, having measurement data can significantly improve the diagnostic process.
FNIRSI FNB58BT USB Cable Tester Malaysia
The FNIRSI FNB58BT USB Tester can be used for USB charging analysis, USB-C cable comparison, charger testing and electronics troubleshooting.
It is suitable for repair technicians, electronics workshops, technical users, engineers and electronics enthusiasts in Malaysia.
If you are unsure whether the FNB58BT is suitable for your USB-C testing application, send us a photo of the charger, cable or device you need to test.
MTM Precision Sdn Bhd
Showroom & Service Centre:
No. 29-1 & 29-2, Jalan Bandar 18,
Pusat Bandar Puchong,
47160 Puchong, Selangor, Malaysia.
Tel: 03-8080 7172
WhatsApp: +6016-660 7346
Email: mtmpre@yahoo.com
Website: www.mtmpre.com.my
Product enquiries are welcome from Selangor, Kuala Lumpur, Johor, Penang, Melaka, Negeri Sembilan, Perak, Pahang, Kelantan, Terengganu, Kedah, Perlis, Sabah and Sarawak.
07 Oct 2026
