Hello! This is M.A. Mustafa from Ornate Pixels. Warm greetings to you all. Today, I am going to discuss one of the most common yet complex problems in LED TV panel repair and its straightforward solution. This issue is particularly frequent in panels built with GOA technology. The symptom is: the screen displays a perfectly normal picture for 1 second, followed by 1 second of flickering, double imaging, or vertical/horizontal lines/bars.
This fault occurs primarily due to a failure in the ODD and EVEN voltage toggling mechanism or an internal leakage short circuit within the panel's built-in GOA/GIP lines. In this comprehensive guide, I will break down GOA technology, the mechanism of ODD/EVEN voltage generation inside the PMIC, and practical bypass repair techniques. Please read this article carefully along with the diagrams to sharpen your LED TV repair skills.
1. What is GOA or GIP? (Gate on Array / Gate in Panel)
GOA stands for Gate on Array, and GIP stands for Gate in Panel.
In older or traditional displays, multiple external Gate COFs (Chip on Flex) were attached around the perimeter of the panel. However, to reduce manufacturing costs and achieve borderless, bezel-less designs in modern slim LED TVs, panel manufacturers eliminated external Gate COFs. Instead, they fabricated the gate driver circuitry directly onto specific tracks of the TFT glass substrate. This integrated gate driver circuit printed inside the glass is known as GOA or GIP.
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Figure 1: Complete architecture of Gate on Array (GOA) / Gate in Panel (GIP) circuit showing signal flow from PMIC/Level Shifter to TFT LCD glass substrate. |
2. What are ODD and EVEN Voltages, and How Are They Generated in the PMIC?
ODD and EVEN are alternating voltage signals designed to turn the panel's odd-numbered (1, 3, 5...) and even-numbered (2, 4, 6...) gate lines or drive blocks on and off.
Internal Mechanism of the PMIC / Level Shifter:
- Static Voltage Generation: The PMIC first generates stable DC voltages via the main DC-to-DC converter circuit: VGH (+26V to +30V) and VGL (-5V to -10V).
- Clock Toggling (1Hz Flip-Flop): Driven by a 1 Hertz (1Hz) flip-flop clock signal coming from the T-Con processor, the LEVEL SHIFTER IC dynamically switches these two static voltages.
- Alternating Signal Output:
- 1st State (1st Second): The ODD pin outputs VGH (+26V) while the EVEN pin outputs VGL (-5V).
- 2nd State (2nd Second): Upon the flip-flop toggle, the ODD pin switches to VGL (-5V) while the EVEN pin switches to VGH (+26V).
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Figure 2: Timing waveform diagram illustrating the 1Hz dynamic voltage toggling between ODD and EVEN signals alternating between VGH (+26V) and VGL (-5V). |
3. Where Do ODD, EVEN, and CKV Signals Go inside the Panel, and What Is Their Function?
There is a widespread misconception that ODD/EVEN voltages connect directly to the gates of individual odd and even TFT pixels—which is technically incorrect.
In reality, the ODD, EVEN, CKV (Clock Vertical), and STVP (Start Pulse) signals feed directly into the Shift Register (Internal Gate Driver Circuit) block built inside the panel glass.
Why Don't They Connect Directly to Pixel Gates?
A 1080p or 4K display contains thousands of horizontal gate lines. If ODD/EVEN connected directly to pixel gates, every odd or even row across the screen would turn on simultaneously. Instead, the Shift Register sequentially triggers VGH line-by-line across the display area.
Primary Purpose of ODD/EVEN Toggling:
- Liquid Crystal Discharge: Ensures the pixel capacitors inside the glass charge and discharge properly to refresh each image frame.
- Preventing TFT Degradation: Exposing microscopic transistors on glass to a continuous direct high voltage causes rapid degradation or short circuits, permanently killing the panel. The alternating flip-flop prevents this static stress.
4. Root Cause Analysis: Why Does the Picture Look Fine for 1 Second and Flicker the Next?
Over extended operating periods, microscopic leakage short circuits develop inside the panel's internal GOA layers or microscopic glass traces.
- During the Second when the Defective Trace receives VGL (-5V): No significant current leakage occurs across the fault path, resulting in a 1-second crystal-clear image.
- During the Second when the Flip-Flop toggles to VGH (+26V): High voltage across the shorted track causes excessive current draw and signal corruption/overlapping. This leads to flickering, double imaging, or vertical lines during that 1-second interval.
5. Bypass Connection Technique and Step-by-Step Repair Procedure
When dynamic switching inside the glass fails due to internal leakage, we can disconnect the PMIC drive tracks and supply a stable static bias (Static Biasing Mode), restoring a 100% stable picture.
Step 1: Identify Tracks and Test Points
Using a digital multimeter set to DC Voltage mode, locate the ODD, EVEN, VGH, and VGL test points near the PMIC on the T-Con or scalar board. You will observe the voltage on the ODD and EVEN pins fluctuating/toggling (e.g., -5V for 1 second, then +26V for the next).
Step 2: Cut the PMIC Tracks (Track Cutting)
Using a razor-sharp precision cutter or surgical blade, carefully cut and isolate the ODD and EVEN lines leading from the PMIC toward the panel entrance.
Step 3: Manual Voltage Bypass Wiring
Solder thin jumper wires to apply direct static voltages:
- Solder ODD Track (Panel Side) ➔ VGL (-5V).
- Solder EVEN Track (Panel Side) ➔ VGH (+26V).
(Note: If double imaging persists with this combination, reverse the wiring—solder ODD ➔ VGH and EVEN ➔ VGL).
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Figure 3: Practical track cutting and voltage bypass diagram for AUO panel repair using M201-2V IC ODD and EVEN pinout. |
6. Why Does Double Imaging Persist If Polarity Is Incorrect?
The panel's internal GOA circuit operates according to strict logic state rules. If you apply incorrect polarity during bypass (e.g., feeding VGH where VGL is required), internal gate transistors fail to turn off and remain continuously latched on. Consequently, residual pixel charges cannot discharge, leaving ghosting, double images, or vertical bars stuck on screen. The picture becomes 100% clear only when the correct bypass polarity opens proper charge-discharge paths.
Conclusion
Mastering panel track cutting and voltage bypass techniques allows technicians to successfully recover many dead or double-image panels without needing costly panel replacements. A word of advice for fellow technicians: always use a high-magnification magnifying glass or stereo microscope while cutting PCB traces to avoid accidentally damaging adjacent tracks.
Watch Practical Video Demonstration
For a complete hands-on tutorial and step-by-step practical guide on fixing double image issues, split pictures, and panel leakage faults, check out my detailed video demonstration from the Ornate Pixels YouTube channel below:
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