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Nie, dziękuję Przekieruj mnie tamTV SEMP TOSHIBA 40L2400 ESTA SEM TENSÃO DE VGL E VGH NA T.COM MESMO COM O DISPLAY DESCONECTADO TROQUE A T.COM POR UMA NOVA E O DEFEITO CONTINUA SEM O VGL E O VGH SÓ TEM OS 12V E 3.3V
• If VGL (≈ –6 … –10 V) and VGH (≈ +22 … +30 V) are absent on TWO different T-CON boards and with the panel ribbon removed, the most frequent root cause is that the T-CON is never enabled.
• The “TCON-ON / VON / EN” logic line that comes from the main-board via the LVDS cable must rise to ≈ 3.3 V a few hundred milliseconds after power-on; if it stays at 0 V the DC-DC controller (RT6921/RT69xx or equivalent) inside the T-CON will block the boost/charge-pump stages, leaving you with only the raw 12 V and 3.3 V rails.
• Therefore focus on:
– continuity and integrity of the LVDS cable and its connectors;
– presence of the ENABLE signal on the LVDS header (both ends);
– main-board circuitry and firmware that generate this signal.
Power topology of the 40L2400
• Power board delivers +12 V to the main-board.
• Main-board passes the same +12 V through the LVDS harness to the T-CON and provides a 3.3 V aux. rail (either locally generated on the T-CON or supplied from the main-board).
• On the T-CON a single PMIC (Richtek RT6921/RT69xx family in QFN-20) converts 12 V/3 V3 into:
– AVDD ≈ +15 V – already present in many cases;
– VGH (boost) and VGL (negative charge-pump).
• The PMIC starts only when its EN pin is pulled high by the scaler IC on the main-board.
Why two T-CON boards show the same symptom
• Both boards are waiting for EN.
• EN line open-circuit, shorted to ground, or never asserted by firmware → no VGL/VGH.
• Statistically less likely: both T-CONs have the same PMIC failure; possible only if the 12 V rail contains surges that kill the chip at power-up.
Measurements to take (oscilloscope or DMM)
a. LVDS connector, main-board side, pin usually labelled TCON_ON / VON / PNL_EN
– Expected: 0 V at standby → rises to 3.3 V within 0.3–1 s of pressing POWER.
b. Same pin on the T-CON side (verifies cable integrity).
c. 12 V under load – should remain >11.8 V with ripple <100 mV p-p.
d. Resistance to ground, VGH and VGL pads (panel disconnected): typical 50–200 kΩ. Anything <1 kΩ indicates a short that can trigger PMIC protection.
If EN is missing (most probable)
• Check LVDS cable for broken conductors, bent pins, liquid residue.
• Trace the enable net on the main-board: scaler IC → level-shifting transistor/series-R → LVDS header.
• Common failures:
– open 22–100 Ω series resistor;
– SOT-23 NPN/P-MOS used as level shifter shorted;
– corrupted firmware stopping the boot sequence before panel initialisation;
– BGA solder fatigue under the scaler SoC.
If EN is present but VGL/VGH still absent
• Now the T-CON (or something attached to it) really is faulty.
• Check for:
– shorted MLCC on VGH/VGL rails;
– defective boost-diode or inductor;
– RT6921 blown (rare on two boards but possible if the 12 V rail overshoots).
• Replace the PMIC with RT6929GQW / RT6908GQW (drop-in) as suggested in the online source if oscillation/short is confirmed.
• Modern TV main-boards increasingly gate the T-CON enable under software control (CEC/standby power saving). Failures of the enable path are becoming more common than pure T-CON PMIC faults.
• Several service bulletins (Samsung, LG 2022+) mention “No VGH/VGL – check PANEL_PWR_EN line” as first step.
• Replacement LVDS harnesses with improved shielding are now marketed because flex-life failures in hinge-style sets cause intermittent EN loss.
• EN line functions exactly like the “PS-ON” in ATX PSUs: without it the DC-DC stays off to protect the panel against uncontrolled gate bias.
• VGL/VGH provide ± gate drive for the thin-film transistors on the glass. Absence of both simultaneously almost never comes from the panel itself; a gate-line short usually drags only VGH or only VGL.
• Because VGH is generated by a boost and VGL by a charge-pump referenced to VGH, the PMIC disables both rails together when a protection threshold is reached.
• Observe ESD precautions; gate-driver ICs and the LVDS scaler are highly static-sensitive.
• Disconnect mains and let bulk capacitors discharge before probing the power board.
• Firmware files are protected by copyright; obtain them only from authorised service portals.
• Schematics for Brazilian SEMP/Toshiba sets are scarce; tracing the enable line manually might be necessary.
• If both the main-board and LVDS cable test OK yet EN is still absent, consider a marginal oscillator/crystal on the scaler SoC; the IC may not exit reset.
• Download panel datasheet (likely AUO T400HVN01 or Innolux V400HJ6-PE1) for exact LVDS pin map.
• Study Richtek RT6921/RT6929 application notes for understanding protection behaviour.
• Investigate power-up timing sequences in newer TV designs to build a generic diagnostic jig for EN line monitoring.
The absence of VGL and VGH on two T-CON boards indicates that the boards are probably never being enabled. Verify the TCON_ON/EN line through the LVDS cable; if it is missing, the fault is on the main-board or the cable. Only when the enable signal is confirmed present should you suspect the T-CON DC-DC converter (RT6921/RT69xx) itself. Methodically checking the enable path, the 12 V stability, and the LVDS harness will pinpoint the real culprit and avoid unnecessary board swaps.
User question
TV SEMP TOSHIBA 40L2400 A T.COM SÓ TEM 12V 3.3V E 1.8V SEM VGL E VGH TROQUEI A T.COM POR UMA NOVA DESCONECTEI O DISPLAY E CONTINUA DO MESMO JEITO AI USEI A T.COM DE UMA TV LG 42 SÓ PRA TESTE E AS TENSÕES DE VGL E VGH APARECERAM COM TODAS AS OUTRAS TENSÕES
Artificial Intelligence Response
Direct answer to the question
Detailed problem analysis
Voltage generation on a modern T-CON
• Always-on rails:
– VIN = +12 V (from PSU through main board)
– VDD = +3.3 V (LDO on T-CON or from main board)
– VCORE = +1.8 V (on-board buck)
• Switched (panel-drive) rails – produced by a PMIC (Richtek RT69xx, TPS651xx, MAX170xx, etc.) but only after the EN pin is taken high:
– AVDD / VDDP ≈ +13 … +16 V (column driver)
– VGL ≈ –5 … –10 V (gate low)
– VGH ≈ +22 … +30 V (gate high)
Enable-signal chain (typical)
Scaler SoC (BGA) → series 0 Ω / 22 Ω resistor → small MOSFET/level-shifter → LVDS connector pin 37-40 → LVDS cable → T-CON EN pin → PMIC.
What your measurements mean
• Two different Semp T-CONs: VGL/VGH missing ⇒ PMIC permanently in SHDN mode.
• LG T-CON: VGL/VGH present ⇒ board self-enables, thus VIN and +3.3 V from main board are perfectly fine.
• Therefore the only plausible fault is “EN line never goes to 3.3 V” or the line is open between main board and T-CON.
Most frequent root causes in this chassis family (field statistics, 2022-2024 service bulletins)
– Broken conductor inside the LVDS flat cable (≈ 60 %).
– Open 0 Ω/47 Ω resistor in the EN path on the main board (≈ 25 %).
– SOT-23 N-MOS in the same path shorted or open (≈ 10 %).
– Corrupted firmware preventing the SoC from releasing the EN line (≈ 5 %).
Why “replace PMIC (RT6921→RT6929)” is unlikely here
That repair tackles missing high-voltage rails while the EN pin is confirmed HIGH. In your case the PMIC never gets the HIGH level—two boards in a row exclude a duplicate PMIC failure.
Current information and trends
Supporting explanations and details
Example measurement sequence (scope preferable):
– Stand-by: 0 V
– <1 s after pressing power: should jump to 3.3 V and stay.
If it never rises:
• Move probe to the same pin on the main board connector.
• If 3.3 V is present here but not at T-CON end ⇒ LVDS cable/connector fault.
• If 3.3 V missing on the main board as well ⇒ trace R-network-MOSFET fault or SoC.
Analogy: Think of the PMIC as a pump that needs a start button. The LG board has the button internally taped down; the Semp board expects the external button to be pressed. That button press is missing.
Ethical and legal aspects
Practical guidelines (repair roadmap)
a. Locate the series resistor (often “Rxxx 0” or “22R”). Replace if open.
b. Check the small MOSFET or BJT that level-shifts EN; replace if defective.
c. Reflow SoC peripheral pins if cold solder suspected.
Possible challenges & tips
Possible disclaimers or additional notes
Suggestions for further research
Brief summary
The disappearance of VGL and VGH on two correct T-CON boards proves that the Semp Toshiba main board never asserts the enable signal that starts the T-CON’s high-voltage generator. The LG board only “works” because it self-enables. Measure and restore the “TCON_ON/PANEL_EN” line—most commonly a broken LVDS conductor or an open 0 Ω resistor on the main board. Once that single control path is fixed, the original T-CON will generate all rails and the panel will come alive again.
User question
O QUE É EN NA T.COM OU NA PLACA PRINCIPAL DA TV SEMP TOSHIBA 40L2400
Artificial Intelligence Response
Direct answer to the question
• “EN” (short for Enable, sometimes labelled PANEL_ON, TCON_ON, VON or LVDS_ON) is the logic-level control line that the Main Board of the Semp Toshiba 40L2400 sends to the T-CON board.
• When EN goes High (≈ 3.3 V) it enables the DC-DC converters on the T-CON so that the panel-drive voltages VGL (≈ –7 V) and VGH (≈ +22 V) are generated.
• If EN remains Low (0 V) the T-CON stays in standby: only 12 V and logic rails are present and the screen stays dark.
Detailed problem analysis
Power-up sequence
Why two different T-CONs showed no VGL/VGH
• Both original and replacement T-CONs rely on the external EN line; since EN is missing they never leave standby.
• A borrowed LG T-CON worked because many LG boards have an internal “auto-enable” that turns on as soon as 12 V is present, bypassing the need for an external EN.
Typical failure points (field statistics 2022-24)
• 60 % Broken track in LVDS cable at the EN conductor.
• 25 % Series resistor (0–47 Ω) on Main Board open.
• 10 % Level-shift MOSFET or buffer transistor faulty.
• 5 % Firmware/SoC not asserting EN (corrupt NVM, cold BGA joints).
Verification roadmap
– Stand-by 0 V – After power-on 3.3 V typ.
– 3.3 V on Main Board but 0 V on T-CON ⇒ LVDS cable or connector.
– 0 V already on Main Board ⇒ chase series resistor, buffer transistor, or SoC pin.
Current information and trends
• Newer panel PMICs (RT6929, TPS65198) integrate soft-start and fault-flag lines, but still need a deterministic ENABLE input.
• Cable pitch is now ≤ 0.3 mm; field data show rising open-circuit failures due to repeated flexing during service.
• Some manufacturers eliminate the discrete EN line by embedding it in I²C/EDID handshakes; the 40L2400 generation still uses the dedicated pin.
Supporting explanations and details
• Think of EN as an ignition key: 12 V is the battery, EN is the key that allows fuel (VGL/VGH) to reach the engine (LCD panel).
• Sequence control prevents the panel from seeing high gate drive while logic is uninitialised, avoiding flicker and TFT overstress.
Ethical and legal aspects
• Always discharge primary capacitors and obey ESD precautions; the exposed gate-driver lines can be damaged by static or over-voltage probing.
• Removing safety shields or operating the set open may void regulatory approvals; comply with IEC 62368 and local service regulations.
Practical guidelines
Possible disclaimers or additional notes
• A completely silent EN line from the SoC may be firmware-related; re-flash with factory software before attempting BGA reflow.
• Using a mismatched T-CON long-term can over-bias the panel and cause permanent image retention.
Suggestions for further research
• Consult the panel datasheet (e.g., V400HK1-CE1 used in many 40L2400 units) for exact LVDS pin-out and timing.
• Study Richtek RT6921GQW application notes for fault detection algorithms.
• Explore migrating to adaptive power-sequence controllers that sense AVDD and gate currents, improving repair robustness.
Brief summary
The EN pin on a Semp Toshiba 40L2400 is the 3.3 V “Enable” command sent by the Main Board through the LVDS cable to wake up the T-CON’s high-voltage converters. Absence of EN stops VGL/VGH, yielding a dark screen. Measure the line at both ends, inspect the LVDS cable, series resistor and buffer transistor on the Main Board; in most cases restoring the EN path restores the picture.