T-Con Board Diagnostics in LCD Televisions
The Timing Controller (T-Con) board is the critical link between the main board and the LCD panel. It receives processed digital video signals via the LVDS cable and generates precise row (gate) and column (source) driver signals that control individual pixel transistors on the panel. Modern T-Con boards also incorporate DC-DC converters that generate specialized voltages (VGL, VGH, VDD, AVDD, and multiple VGMA gamma reference voltages) essential for proper panel operation.
Faulty T-Con boards are responsible for a significant percentage of display-related complaints brought to repair centers on Luthuli Avenue, particularly in brands such as Samsung, LG, Sony, Hisense, Vitron, and TCL.
Common Symptoms Indicating T-Con Failure
- Vertical or horizontal lines/bars (single or multiple, colored or white/gray).
- Double image, ghosting, or solarization (negative-like picture).
- Half-screen dark or completely white/gray while the other half works.
- Full-screen distortion, color inversion, or washed-out image.
- No picture at all, yet faint image is clearly visible with flashlight test and backlight is confirmed working.
- Intermittent display issues that change with gentle pressure on the panel bezel or ribbon cables.
- Screen shows image only after prolonged warm-up or only when cold.
Systematic Diagnostic Procedure
- Preliminary Confirmation Perform the flashlight test: In a darkened room, shine a bright torch at an acute angle onto the screen while the TV is on. A clear but faint picture confirms that the backlight, power supply, main board video processing, and panel itself are functional — isolating the fault to the T-Con or its connections.
- Visual & Mechanical Inspection Open the rear cover and locate the T-Con board (usually centrally mounted and shielded, connected directly to the LCD panel via flat ribbon cables). Check for:
- Obvious burn marks, swollen capacitors, or cracked components.
- Poor seating or oxidation on LVDS cable and panel ribbon cables.
- Cracked or damaged flex cables (common on edge-type T-Cons).
- Cable Reseating & Cleaning More than 40 % of apparent T-Con faults in Nairobi workshops are resolved simply by:
- Unplugging and firmly reseating the LVDS cable at both ends.
- Carefully cleaning ribbon cable contacts with 99 % isopropyl alcohol and a soft brush or lint-free cloth.
- Gently pressing along the ribbon cable length while observing the screen — temporary image improvement confirms poor contact.
- Voltage Measurement on T-Con Board With the TV powered on, measure the following key voltages (refer to board silkscreen or service manual for exact test points):
- VIN or VDD: typically 10–16 V input from power supply (must be stable).
- 3.3 V or 5 V logic supply.
- AVDD: usually 15–18 V (boosted for source drivers).
- VGH: +20 V to +35 V (gate high).
- VGL: –5 V to –15 V (gate low).
- VGMA/VCOM voltages (multiple gamma references). Any missing or severely out-of-spec voltage immediately points to either a faulty DC-DC converter on the T-Con or a power supply issue feeding it.
- Partial Substitution Test (Definitive Confirmation) Temporarily substitute the LVDS cable with a known-good one of matching pin count and length. If possible, swap the entire T-Con board with an identical part-number unit from a working donor set of the same panel type. Immediate restoration of perfect picture confirms the original T-Con was defective.
- Distinguishing T-Con Fault from Panel Fault If lines or distortions move or change when gentle, even pressure is applied to different areas of the screen bezel, the fault is usually in the panel’s COF (Chip-On-Film) tabs or TAB bonds — which are unfortunately uneconomical to repair. A completely static defect that does not respond to pressure or heat/cold usually indicates a repairable T-Con issue.
Repair Options
- Ribbon cable cleaning/reseating/LVDS replacement → often resolves the issue at minimal cost.
- Component-level repair → replacement of failed DC-DC ICs, gamma buffer chips (e.g., AS15, AS19 series), or shorted multilayer ceramic capacitors (requires hot-air microsoldering).
- Full T-Con board replacement → most reliable and common solution at Luthuli Avenue workshops. Exact part-number matching is mandatory (e.g., 6871L-XXXXXX, ST3151A05-X, LJ94-XXXXX).
Professional technicians at Prologic-Technologies routinely perform these diagnostics within minutes and can confirm whether a T-Con fault is present or if the more expensive LCD panel itself has failed. Accurate diagnosis prevents unnecessary expenditure and ensures cost-effective repair.
For any LCD television displaying the symptoms described above, prompt professional diagnostics on Luthuli Avenue is strongly recommended.