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• The Samsung BN44-00339A SMPS/LED-driver board most frequently fails in five areas:
1. Stand-by section → No power / no LED
2. Main‐converter or PFC section → Blown fuse or continuous relay “clicking”
3. Secondary regulation → Intermittent shut-down / cycling
4. LED-driver section → Sound but no picture (dark screen)
5. Aging electrolytics / bad solder → Instable voltages, audible buzz
• >90 % of repairs involve replacing a handful of electrolytic capacitors (e.g. CM802, CP814), shorted MOSFETs (QP801S, QM801/802), opto-couplers, or re-soldering cracked joints on the back-light transformer TM801S.
• Systematic troubleshooting – visual inspection, verify 5 V-STBY, force PS-ON, measure PFC (≈390 Vdc), check 13 V / 5.3 V rails – quickly isolates the defective subsection.
Complete power failure (no 5 V-STBY)
• Symptoms: TV totally dead, standby LED off.
• Typical culprits
– CM802 (47 µF / 50 V, high ESR) starves PWM IC;
– ICP801 (ICE2AP01/FAN7530M) Vcc pin never reaches start-up threshold;
– FP801S 4 A fuse open → usually after QP801S (FQPF9N50C) or bridge BD801S shorts.
• Fix: Replace CM802 (+ other 105 °C, low-ESR caps), check PWM Vcc (~15 V). Replace shorted MOSFET/rectifier before fitting a new fuse.
Stand-by OK but no start-up / constant relay clicking
• Symptoms: red LED on, relay ticks every 0.5-1 s, screen dark.
• Root causes
– PFC or main resonant FETs (QM801/QM802, QP801S) short → PSU trips;
– Opto-coupler IC801S or TL431 shunt drift → feedback loop unstable;
– Secondary filter caps on 13 V rail (CM851/2/6) > 1 Ω ESR.
• Diagnostics: Assert PS-ON high manually (jumper 5.2 V-STBY to PS-ON). If rails collapse under load, scope shows saw‐tooth.
• Fix: Replace defective FETs (check driver gate resistor & current-sense Rs801, 0.2 Ω); recap 13 V bank with 105 °C low-ESR parts.
Intermittent shut-down / reboot after minutes
• Causes: thermal drift of opto-coupler CTR, cracked solder on hot parts (TM801S, choke L801S), dried bulk caps (CP809 150 µF/450 V, CP814 10 µF/450 V).
• Solution: Re-solder entire hot side, replace suspect capacitors, renew thermal compound on FET heatsinks, clean dust.
Backlight / “sound but no picture”
• Symptoms: Audio present, faint image visible with torch, no back-light.
• Failure points: LED-driver FET QIC801 short/open, transformer TM801S dry joints, HV cap CP812 1 µF / 250 V open, or open LED string in panel.
• Tests: Back-light tester on CNL802; PSU will deliver ≈200 V then shut if open-circuit detected.
• Fix: Reflow TM801S pins, replace QIC801 & CP812; if LED string open, service panel strips.
Audible coil whine / fluctuating 12 V
• Usually secondary output caps or TL431 reference drift. ESR > 1 Ω causes ripple, audible in chokes TMS.
• Recap CM857/858 (12 V) and verify opto/TL431.
Key component map (silkscreen may vary by revision)
• Primary fuse – FP801S • Bridge – BD801S • PFC MOSFET – QP801S
• Stand-by PWM IC – ICP801 • Main resonant FETs – QM801, QM802
• Critical caps – CM802 (stand-by), CP809/814 (PFC bulk), CM851-856 (13 V)
• Opto feedback – IC801S + TL431 (ZM801)
• Back-light driver – TM801S, QIC801, CP812
Electrical wave-forms of a healthy board (230 V mains):
PFC bulk: 390 Vdc flat • LLC resonance: 400 kHz burst • 13 V rail ripple < 50 mVp-p
• Field reports (Badcaps 2023-2024, Elektroda 2024) still list CM802 and CP814 failures as the #1 cause of dead sets; modern low-ESR polymer replacements markedly improve MTBF.
• Asian vendors now sell “BN44-00339A repair kits” – includes CM802, CP814, QP801S, FP801S, opto and TL431 – for < US$10.
• Because LED strips age, back-light failures have eclipsed power MOSFET shorts as the most frequent 2024 service call.
Snubber & EMI: When QP801S fails, RC snubber (RS806 / CS806) often overheats; replacement prevents ringing that can kill new FETs.
Opto-ageing: CTR of PC817 drops ~2 %/khr at 100 °C; below 50 % feedback loop mis-regulates → cycling.
ESR effect: Ripple \( \Delta V = I \times ESR \); at 2 A, ESR 1 Ω → 2 Vpp, enough to trip OVP.
• Mains-rated work must follow IEC 60950-1 / UL 62368 safety rules.
• Always isolate and discharge – residual 400 V can be lethal.
• E-waste: Faulty boards contain Pb in solder; dispose under WEEE / local e-waste regulation.
Common pitfalls & fixes
• New fuse blows instantly → missed shorted gate-driver IC or snubber diode.
• Board powers on bench but not in set → mainboard short; isolate and diagnose separately.
• High inrush after recap → use NTC resistor identical to original RT801S.
• Board revisions A/B/C use slightly different IC designators; always cross-check schematic.
• Some failures are secondary to lightning surge – hidden carbonised PCB tracks may require board swap.
• DIY repair voids manufacturer warranty.
• Study long-term ESR drift of miniature electrolytics at 90–100 °C to model pre-emptive recap intervals.
• Investigate replacing CM802 with 47 µF polymer to eliminate most start-up failures.
• Evaluate conformal-coating hot-spot areas to reduce moisture-induced leakage.
BN44-00339A failures cluster around dried electrolytics, shorted MOSFETs, and fatigued solder joints. A disciplined workflow—verify 5 V-STBY, force PS-ON, measure PFC bulk, scope rails, then component-level testing—resolves the majority of cases. Upgrading caps to 105 °C low-ESR types, renewing thermal paste, and reflowing back-light transformer joints restore full function and extend service life well beyond the original design margin.
