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• On a Philips 55OLED903, “T-CON not functioning” normally means the panel’s timing-controller/driver section is no longer generating the secondary voltages and pixel-clock signals the OLED cell needs.
• First confirm the set actually delivers the 12 V supply and LVDS/eDP data from the main board; if those are present, measure the on-board rails (AVDD ≈ 15–17 V, VGH ≈ 27 V, VGL ≈ -6 V, VDD 3 V/1 V8).
• If one rail is missing or a surface-mount fuse is open the T-CON/COF has a hard fault or is being shut down by a shorted driver IC inside the panel.
• Because the 55OLED903 uses an LG OLED open-cell with bonded “COF” drivers, the T-CON is an integral board at the top edge of the panel; practical repair is therefore either:
1) locate and remove the shorted component(s) or repair the DC-DC converter, or
2) replace the entire panel assembly (economically doubtful).
Architecture
• Main board → LVDS/eDP flex → T-CON/COF board (top-edge PCB) → 8–12 bonded driver ICs.
• T-CON generates:
– Pixel data timing (CLK, STV, OEV)
– Analog rails (AVDD, VGH, VGL, VCOM) via an on-board buck/boost converter.
Typical failure signatures
• Set powers up, standby LED & audio OK, screen completely black.
• Vertical coloured lines, half-screen, or rapid flicker.
• 12 V fuse on T-CON open or very low resistance (<5 Ω) on any rail → shorted ceramic cap / COF IC.
Step-by-step diagnosis (live-set precautions, ESD strap, isolated bench)
a) Visual: burnt spots, cracked 0402 caps, corroded flex contacts.
b) Continuity: F1 (12 V) and F2 (logic 3 V3) should read <0.2 Ω.
c) Power-on measurements (chassis ground reference):
• TP-VIN ≈ 11.5–12.6 V
• TP-3V3 ≈ 3.3 V
• TP-AVDD ≈ 15–17 V
• TP-VGH ≈ 25–30 V
• TP-VGL ≈ -5 to -10 V
d) If VIN is present but the converter shuts down, disconnect one ribbon at a time (“half-screen test”). Return of rails after one ribbon is pulled = panel-side short; nothing returns = T-CON fault.
Distinguishing main-board vs T-CON vs panel fault
• 0 V at the T-CON fuse → main board or PSU 12 V rail.
• 12 V present, secondary rails missing on both halves → T-CON converter or controller IC.
• 12 V present, rails return with one ribbon unplugged → shorted COF / panel, not reparable.
Repair options
• Component-level: replace shorted MLCC (often 10 µF/25 V) or the TPS651xx/TI-like triple-converter IC using hot-air and microscope.
• Board swap: Not possible separately; the board is factory-bonded to the glass.
• Panel swap: Requires LGD V18 55-inch 4K OLED cell (cost frequently >70 % of new TV).
Tools
• DMM with µΩ range, 100 MHz scope (optional), hot-air station, Kapton tape, liquid flux, IR preheater.
• LG Display’s 2020-onward OLED cells moved even more power regulation onto the panel, making discrete T-CON replacement impossible for consumer repair.
• Professional shops increasingly use “inject-low-voltage and thermal camera” techniques to locate <1 Ω shorts on driver PCBs.
• Market trend: panel availability dropping as Philips/TP-Vision migrates to newer Meta/OLED.EX panels; legacy 55-inch 2018 glass is becoming scarce.
• Negative VGL rail is mandatory for turning OFF the TFT gates. Absence of VGL typically yields an all-white screen or full black with heavy current draw—hence fuse blowing.
• The half-screen ribbon test works because each side’s COF drivers are electrically independent; isolating a short removes the over-current condition.
• High-voltage sections (400 V PFC on the PSU) remain energized—technician must follow IEC/EN 62368 safety rules.
• Replacing panels involves proper disposal of e-waste; OLED glass contains indium and should be recycled.
• Entering service mode may void the manufacturer’s warranty or disrupt NVM calibration.
• Start with non-invasive steps (reseat cables, measure VIN).
• Always short the 1 µF HV cap on the boost rail with a 10 kΩ resistor before soldering.
• When using hot-air, shield adjacent COF bonds with copper foil to avoid delamination.
• If rails pulse on/off at ≈2 Hz, suspect the buck-boost IC has detected over-current—look for <10 Ω on the affected rail.
• Because the T-CON is integral, a “board only” purchase advertised online is often harvested from cracked panels—verify bonding tabs are intact.
• Even after a successful component repair, panel-level ageing compensation data is stored in NVM on the SSB main board; keep original main board with the repaired panel.
• Study LG Display patent US9,773,414 for the multi-rail converter topology used on V17/V18 OLED cells.
• Investigate automated short-location methods (thermal imaging, lock-in thermography).
• Monitor TP-Vision service bulletins for firmware that mitigates T-CON over-current false trips.
A non-functioning T-CON in the Philips 55OLED903 almost always points to a failure on the panel-mounted timing/driver PCB. Confirm 12 V supply first, then verify the secondary rails. Loss of any rail or an open on-board fuse localises the fault to the T-CON section; disconnect-one-ribbon testing differentiates an internal T-CON failure from a shorted COF driver in the glass. Because the board is integral to the panel, repairs are limited to component-level work or replacement of the entire panel assembly. Proceed only with proper instrumentation and safety practice; otherwise engage a professional service centre.
