LED backlight strips are one of the most failure-prone components in modern LCD / LED TVs. When the screen is very dim or black segments appear, testing the backlight strips becomes critical. This guide walks you through step by step methods to check whether your TV’s LED backlight strips are functioning (or failing), and how to isolate the problem.

Basic Safety and Preparation

Before you begin any testing, take these precautions:

• Disconnect the TV from power and unplug from the wall.

• Wait 5–10 minutes to allow capacitors to discharge.

• Use ESD (electrostatic discharge) protection — wear a grounded wrist strap if possible.

• Work in a well-lit area, and organize tools (multimeter, power supply, cables) before disassembly.

• Document screw locations and cable routing; take photos so you can reassemble properly.

You will need:

• A digital multimeter (with diode / continuity / voltage modes)

• A regulated DC power supply (with adjustable current limit)

• Alligator clip leads or test probes

• Schematic or backlight driver board information (if available)

How LED Backlight Strips Work (Brief Overview)

Understanding basic operation helps in diagnosis:

1. LED strips are strings of small LEDs in series (often 6, 8, 12, or more), sometimes with resistors.

2. The backlight driver board feeds a high constant current through the string; the voltage across the strip is typically tens of volts.

3. If one LED fails open, the whole string is dark (no current flows).

4. If an LED fails short, it may reduce brightness or change color, but might not totally disable the strip.

5. Some strips are “side-lit” (mounted along edges), others “direct/array” (behind panel). Testing applies similarly, though layout differs.

Step 1: Visual Inspection

Start with a non-powered visual inspection:

• Check for burn marks, cracked traces, detached solder joints, or obvious physical damage.

• Inspect connectors and wiring from the strip to the backlight driver — loose or corroded connectors often cause failure.

• Examine for discolored or “blackened” LED surfaces (sometimes visible under magnification).

If a section is physically damaged, that segment might be isolated and bypassed, or replaced entirely.

Step 2: Continuity / Resistance Check (without power)

Using the multimeter:

1. Set the multimeter to resistance (Ω) or diode / continuity mode.

2. Place probes across the input and output terminals of the LED strip.

3. A valid strip with all LEDs intact should show some measured resistance, not infinite.

• If it reads OL / infinite, the strip is likely open (broken internal connection).

• If it reads a very low resistance (almost short), some part may be shorted.

4. To isolate the section, you can divide the strip into sub-segments (if you can access points between LED groups) and test each segment.

Note: Because LED strings have directional junctions, the reading may vary depending on polarity. You may need to reverse probes to check diode behavior.

Step 3: Forward Voltage / Voltage Drop Test

If the resistance check appears plausible, you can measure approximate forward voltage:

• Set the multimeter to DC voltage.

• Apply a small low current (if your meter has a diode mode, it injects ~1 mA or so).

• The meter might display a forward voltage drop (e.g. 20V, 30V) for the entire string.

• If one LED is open, you will see no voltage or zero reading.

This is a gentle test because it uses low current, thus low risk to the strip.

Step 4: Power Supply / Jumper Test (with Caution)

This is a more direct method. Use a regulated DC power supply with current limit:

1. Determine the correct operating voltage and current for the strip (from datasheet or by measurement on a known good strip).

2. Set the supply to the expected voltage (slightly lower) and a safe current limit (e.g. 20–50 mA above expected).

3. Connect positive and negative leads to the strip’s input pads.

4. Observe whether the strip lights up:

• If it lights fully and uniformly, the strip is good.

• If it flickers, only some LEDs light, or remains dark, there is a failure.

• Gradually increase voltage up to nominal, as long as current remains controlled.

5. During this test monitor current. If current spikes or supply enters current limit, stop to avoid damage.

This method is useful especially when the strip is removed from TV and isolated.

Step 5: Sectional Bypass and Sub-String Testing

When a long strip fails, you can isolate trouble areas:

• Use wire jumpers to bypass certain sections (e.g. bypass the first 3–4 LEDs) and see whether the remainder lights.

• If the rest works, the bypassed section holds the fault.

• You can progressively narrow down to the exact LED or trace.

This is more advanced and requires care, because wrong bypassing may cause overcurrent in remaining portions.

Step 6: Testing In-System Using Backlight Driver Board

Sometimes you might not detach strips. Instead:

1. Power on the TV (carefully) until the panel is showing very dim image or LED driver is active.

2. Use an infrared camera (or phone camera in night mode) to detect faint glow of LED segments through the panel.

3. Use a multimeter voltage probe (if safe access) to measure output from the backlight driver to strip.

4. Compare across multiple strip connectors — if one connector outputs correct voltage but the strip doesn’t light, the strip is suspect, not the driver.

Be cautious: some driver boards drive strips at high voltages that may harm the meter or you if done improperly.

Table: Summary of Test Methods

Tips for Reliable Testing

• Always start gentle and low current, then gradually move toward normal operating conditions.

• Use current-limited supply to protect against catastrophic short circuits.

• Keep track of polarity — LEDs are directional.

• Replace or bypass faults only after careful localization.

• Always recheck after repairs before full reassembly.

When to Replace Versus Repair

If multiple LEDs or segments are failing, oftentimes replacement of the entire strip is more reliable and cost-effective than attempting to repair individual LED elements, especially for densely packaged modern strips.

Suppliers like StarSharp offer LED tv backlight strip products in a wide range of models and sizes. Their catalog includes edge strips and direct backlight arrays, across many TV brands and sizes. For professionals or DIY repairers needing quality replacement strips, StarSharp is a viable option to source parts.