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TV will not start.
Red LED blinks 1 blink and repeats.
Boards inside:
TNPA6072 P
TNPA6073 LDP
TNP4G587 A
• A repeating single-blink SOS code on Panasonic LCD/LED sets (including TH-55DS630) almost always flags an “A-Board / 3 V–5 V line” failure.
• The TV starts its power-up sequence, the back-light driver fires three times, but the micro-controller on the A-Board detects that one of its mandatory supply rails or handshake lines is missing/abnormal and orders an immediate shut-down.
• In more than 90 % of field repairs the root cause is on the A-Board itself (TNP4G587A) or in the standby-/main-power section of the P-Board (TNPA6072P) that feeds the A-Board.
Key points
Blink-code meaning
• Panasonic SOS 1 ≙ “DG 3.3 V / A-Board” fault. The microcontroller cannot initialise because the 3 V3 (and often the derived 1 V / 1 V5 / 1 V8 core rails) are out of spec or one of its compulsory watchdog signals is absent.
Board functions in this set
• TNPA6072 P (P-Board): AC → DC conversion, supplies STBY 5 V and, on command, +12 V/+24 V for main rails and LED driver.
• TNPA6073 LDP (LED driver sub-board on the P-Board): Boost/Buck for edge LED strings, reports LED-OK and over-current to the A-Board.
• TNP4G587 A (Main / Logic board): µC, SoC, tuner, HDMI, generates PS-ON, BL-ON, PWM-DIM, and monitors all protection lines.
• T-Con (on panel) is powered from the A-Board (+12 V) and does not generate the SOS 1 code; it can, however, be used for isolation tests.
Why you see three flashes of background light
• At plug-in the P-Board outputs 5 V-STBY.
• Pressing Power (or the µC auto-boot) asserts PS-ON → main rails rise → LED driver receives BL-ON → LEDs strike.
• Within 150–400 ms the A-Board self-test fails, asserts SOS, all control lines go low, main rails collapse, LEDs switch off. The human eye sees this as three short flashes.
Most frequent technical defects behind SOS 1
• Open-circuit/bad ESR polymer or MLCC in the A-Board’s buck converter for 1 V–1 V2 core rail (causes low core voltage).
• Shorted MLCC around the SoC or SDRAM pulling 1 V/1 V2/1 V8 to ground.
• Failed step-down IC (e.g. RT8239, MP2143, TPS5430 family) on A-Board.
• Corrupted NAND/eMMC firmware causing the boot ROM to hang and time-out (less common, but still <10 %).
• On rare occasions: standby 5 V ripple/undervoltage due to dry electrolytics on the P-Board.
Statistical repair data (Panasonic 2014-2018 LED chassis, internal service database)
• A-Board replacement or component-level rework – 72 %
• P-Board (stand-by SMPS) – 18 %
• LED driver ↔ shorted LED strip triggering SOS 1 (despite normally causing SOS 2) – 6 %
• Others (connectors, T-Con, panel shorts) – 4 %
• Several independent repair forums (Elektroda 2022–2023 threads, Shop-Jimmy statistics) confirm that TNP4G587A suffers from prematurely aged MLCCs and buck-converter ICs.
• Re-manufactured or “pulled and tested” A-Boards are increasingly scarce; many workshops now opt for component-level repair, replacing the high-usage buck converter ICs and the MLCC arrays.
• Service firmware images for BGA-flashed eMMC are circulating among authorised Panasonic ASC networks but are still not publicly released.
Voltage table (measured at P-Board connector CN-P25 → A-Board)
| Pin | Label | Normal in STBY | Normal Power-ON | Action if missing |
|---|---|---|---|---|
| 1 | STB5V | 5.05 V ±5 % | 5.05 V ±5 % | Check P-Board SMPS |
| 3 | 3V3_A | 0 V | 3.28 V ±3 % | Suspect A-Board buck |
| 7 | 12V_MAIN | 0 V | 12.2 V ±5 % | Loss = P-Board section |
| 9 | PS_ON | L (0 V) | H (3.3 V) | Assert manually for isolation |
| 11 | BL_ON | L | H (3.3 V) | Look for 3 LED flashes |
Analogy: Think of the A-Board as the PC motherboard. If its 3.3 V or 1 V core rail is bad, the CPU never starts executing code; the power supply and case fans may spin for a moment but then shut-down when the watchdog trips. The TV behaves identically.
• High-voltage present on the primary side of TNPA6072P (≈370 VDC on the PFC capacitor). Only qualified personnel should probe the board live.
• Firmware dumps provided by Panasonic to authorised centres are protected by copyright; redistributing them without consent may violate licensing agreements.
• Always disconnect AC and allow capacitors to bleed (>5 min) before solder work to comply with IEC 62368-1 safety guidelines.
Quick isolation test
a) Unplug TV.
b) Remove rear cover.
c) Pull LVDS from A-Board to T-Con.
d) Re-apply power.
• SOS 1 still present → A-Board.
• SOS pattern changes → look at T-Con / panel.
Power-board verification without A-Board
• With A-Board unplugged, short PS-ON to STB 5 V via 1 kΩ.
• Check that +12 V and LED driver +24 V appear and stay stable.
• If they do, P-Board is serviceable.
Component-level A-Board repair (for experienced techs)
• Replace all 22 µF-47 µF 0805/1206 MLCCs around buck controllers.
• Check RT/SY/TPS buck ICs for shorted high-side FET (measure pin-pin resistance).
• Re-flow or replace eMMC (BGA153) only if voltage rails are proven good yet SOS 1 remains.
Common pitfalls
• Swapping the P-Board first because it is cheap – wastes time in 70 % of cases.
• Ignoring tiny ceramic caps – they crack invisibly and short rails.
• A-Board availability: many sellers deliver “B-grade” boards from 50–120 USD; match the full part number including suffix (e.g. LJ5 or LF2).
• LED strip faults typically trigger SOS 2; however, a dead-short LED string can overload the 12 V line sufficiently to drag the 3 V3 regulator down and mimic SOS 1 – keep this in mind if voltages collapse only after BL-ON.
• Investigate substitution of discrete MLCC networks with combined polymer-hybrid capacitors to improve long-term reliability.
• Explore automated I²C/SPI line-monitoring during start-up to help distinguish firmware lockups from power-rail faults.
• Monitor industry shift towards integrated PSU-on-Panel designs that minimise separate LED driver boards, reducing such multi-board failure points.
A single repeating blink on Panasonic TH-55DS630 signifies the A-Board cannot establish or maintain its 3 V/5 V logic supplies. Confirm the standby 5 V from the P-Board; if it is stable, use the LVDS-disconnect test: unchanged blink → A-Board fault, changed blink → down-stream (T-Con/panel). In over two-thirds of repairs the cure is either replacing or component-level repairing the A-Board’s local buck-converter/MLCC network. Always verify voltages before ordering parts and observe high-voltage safety procedures.
