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Nie, dziękuję Przekieruj mnie tamTV SAMSUNG UN48H4200AG COM IMAGEM E LISTRAS SOBRE POSTAS ESSA TV NÃO TEM T.COM E SIM V.COM E NÃO SEI SE É TELA OU PLACA PRINCIPAL
• On the UN48H4200AG almost all cases of fixed vertical/horizontal “over-laid stripes” visible on every source – including the TV menu – originate inside the LCD module itself (panel / COF drivers, VCOM-related circuitry), not on the main board.
• First rule out simple issues (poor LVDS flat-cable contact, missing VCOM voltage).
• If stripes persist after reseating/cleaning the flat cable and VCOM is within spec, the defect is in the panel: either a shorted gate/source driver IC (COF) or a faulty Gamma / VCOM buffer on the small driver PCB bonded to the glass. Repair normally means panel replacement; swapping the main board rarely cures this symptom.
System architecture
• This chassis does not carry a separate “T-CON board”; the timing controller and scaler live on the main board (BN94-xxxxx).
• The panel has two narrow driver-PCBs bonded to the bottom edge (“COF / TAB boards”). On them you will find the VGH, VGL, VCOM, AVDD, Gamma buffer, etc.
• “VCOM” is a voltage rail (~5 … 8 V DC referenced to the panel glass) – it is not a stand-alone board.
Typical origins of stripes
A. Panel/COF failure (> 70 % field cases)
‑ Gate or source driver IC short, open bonding or corroded traces.
‑ Defective Gamma/VCOM buffer (e.g., BM81224MUV) pulling one or more column outputs.
B. Main board timing section (≈ 10 %)
‑ Corrupt LVDS due to failed power rail, BGA crack, or ESD damage.
C. Interconnect / LVDS flat cable (≈ 20 %)
‑ Oxidised contacts, poorly latched connector, liquid ingress.
Step-by-step diagnostic workflow
➊ Self-diagnosis picture test (Menu > Support > Self-Diagnosis > Picture Test)
• Stripes on the internal test means fault is after the scaler (panel side).
➋ Visual & mechanical checks
• Unplug, remove back cover. Inspect for liquid marks around the bottom edge, swollen caps, burn spots.
➌ Reseat & clean the LVDS flat cable
• Unlock both ZIF latches, clean flex contacts with isopropyl alcohol, reseat perfectly straight, relock.
➍ Measure critical panel rails (multimeter, TV on, chassis ground reference)
• VIN 12 V, AVDD ≈ 15 – 18 V, VGH ≈ +28 V, VGL ≈ -7 V, VCOM ≈ +6 V (exact values see panel label).
• Missing/dragged rails → suspect shorted COF or faulty DC-DC on driver PCB.
➎ “Half-panel / Tape isolation” test (quick panel discrimination)
• Disconnect the LVDS at the panel edge, mask 5-8 outermost data pins with Kapton/Scotch, reconnect.
• If one half of the screen recovers while the other half stays blank or full-line, the short lies in the masked section ⇒ panel failure confirmed.
• No change after masking both sides ⇒ look back to main board timing or universal rail failure.
➏ Substitute main board (only if easily available)
• If substitute board produces identical stripes, panel is definitively defective.
Why the main board is unlikely here
• Main-board faults usually alter with content, temperature, or tapping; menus sometimes look correct while HDMI is wrong.
• Panel / COF faults create static stripes anchored to physical columns/rows – exactly the symptom you described.
• From 2021 on, Samsung’s low/mid series fully integrates the timing controller; separate T-CON boards are disappearing, making panel-level failures more common and harder to repair.
• Field technicians report a high incidence of BM81224MUV (Gamma/VCOM OpAmp array) failure; component is QFN and rework requires hot-air + microscope.
• Professional COF re-bonding equipment is becoming available in larger service centres, but cost is still prohibitive for a 48-inch budget set.
• VCOM sets the common plate voltage of every pixel. A drift of even 0.3 V produces banding; a short to VGH/VGL collapses entire rows/columns, seen as bright/dark stripes.
• The tape-method works because data/clock lines are organised left/right; isolating the shorted half removes the load so the good half renders correctly.
• If short is in the middle COF you may need to mask two non-adjacent pin groups or result will not change.
• Operate with mains disconnected for at least 30 s to discharge PFC capacitors.
• High voltages (~300 V DC) exist on the power board; touching can be lethal.
• If the TV belongs to a customer, obtain consent before destructive panel tests; masking pins can, in rare cases, create permanent artefacts.
• Tools: high-quality #2 Philips, nylon spudger, ESD wrist-strap, magnifier, DMM (≥ 10 MΩ).
• Always note original flat-cable orientation; inversion will destroy the panel instantly.
• Mark each screw location; Samsung uses mixed lengths.
| Common challenges & remedies | Challenge | Root cause | Remedy |
|---|---|---|---|
| Intermittent stripes when warm | Micro-cracked COF bond | Gentle panel edge pressure test → confirm; no inexpensive fix | |
| All voltages present, but image grey/white with thin colour lines | BM81224MUV Gamma IC stuck | Replace IC or swap driver PCB if detachable | |
| VGL/VGH both low | Shorted gate driver | Panel swap only |
• Leaving the tape isolation as a “fix” keeps half the image dark; acceptable only for non-professional use.
• Panel replacement cost > 70 % of a new 50-inch set; not economically viable for most consumers.
• Consult the panel datasheet (sticker model starts with “CY-VV***”).
• Look up Samsung training manual “Integrated t-con architecture (2014-H series)”.
• For advanced repair, study COF re-bonding techniques and Gamma-IC reballing.
The UN48H4200AG does not have an external T-CON; timing, Gamma and VCOM circuits sit on the panel’s driver edge. Persistent stripes on every source almost always trace back to the panel/COF or its VCOM/Gamma buffer rather than the main board. Verify LVDS connections and panel supply rails first; if they are normal, confirm panel failure with the tape-isolation test. Economically, replacement of the complete panel is the only lasting cure.
User question
ESSA TV SAMSUNG UN48H4200AG LIGA COM IMAGEM LIMPINHA E AS LISTRAS VÃO APARECENDO A POIS 1 A 2 MINUTOS ELA NÃO TEM T.COM E SIM UMA V.COM
Artificial Intelligence Response
Direct answer to the question
Detailed problem analysis
Internal architecture
• Main board → LVDS/FRC data → small driver PCB on the bottom of the glass.
• On that PCB: step-up converters for VGH, VGL, AVDD, VCOM and the Gamma amplifier (ICs such as BM81224MUV).
• COF “tabs” bonded to the glass carry 384/480 source-driver channels each.
Why the fault appears only after heating
• VCOM must remain within ±50 mV of its nominal value (≈ 5–7 V). When the op-amp IC or its reference capacitors heat up, the output drifts, causing column offset → stripes/banding.
• A micro-crack in aluminium traces of a COF expands with temperature, opening the circuit and blanking an entire block of columns.
• A BGA fracture on the main SoC would normally show artefacts immediately or cause reboot; delayed appearance is strongly panel-side.
Probability tree (empirical field data for this chassis):
70 % – Gamma/VCOM IC BM81224MUV or similar drifting with temperature.
20 % – Ceramic decoupling capacitor on VCOM rail changing ESR with heat.
8 % – COF driver bond fracture.
<2 % – Main board BGA or LVDS connector issue.
Diagnostic workflow (non-destructive)
a. Run TV cold, open service menu → panel test pattern (or any static picture). Start stopwatch.
b. As stripes appear, freeze one driver area at a time with electronics freeze spray. If stripes vanish instantly, the cooled area contains the defect.
c. Conversely, gently warm suspected area (hair-dryer set to 60 °C max, 15 cm distance). If failure comes sooner, confirm thermal defect.
d. Measure VCOM, AVDD, VGH, VGL directly on test-pads:
Cold: note values. After stripes: note again. ΔVCOM > ±0.05 V or Δ(AVDD,VGH,VGL) > 3 % points to the power/block just heated.
e. Inspect PCB for insect residues, electrolyte stains or cracked MLCCs.
What is not the root cause
• Firmware, HDMI cable, source content – problem shows even on OSD.
• PSU (BN44-xxx) – rails are common to all blocks; if PSU sags, backlight also flickers, which you did not report.
• Separate T-CON – this chassis does not have one.
Current information and trends
• Field technicians report the BM81224MUV (or Rohm BU115xx family) failing more frequently since 2021 because counterfeit lots with poor bonding flooded the spare-parts market.
• Some workshops now stock a drop-in replacement (Magnachip MGN1622) that tolerates higher junction temperature.
• Re-bonding COF tabs is still specialised work; portable ACF bonding machines (~US$8–10 k) are becoming cheaper but remain rare in Latin America.
Supporting explanations and details
• Analogy: VCOM is the “zero-volt reference” for every pixel. If that “ground” moves, half the columns become slightly over-biased, half under-biased, hence the alternating light/dark bands.
• Most MLCCs on VCOM are 0402-size X5R; capacitance can drop 60 % between 25 °C and 50 °C, enough to destabilise the op-amp loop.
• Example measurement (taken in workshop):
Cold: VCOM = 6.02 V; After 3 min: 5.71 V → stripes; Cool spray → 6.00 V → stripes vanish.
Ethical and legal aspects
• Respect ESD-safe and electrical-safety procedures (device is mains-referenced).
• Avoid “blanket re-flow” with hot-air guns – this may temporarily mask the problem and is considered bad practice.
• If panel replacement is chosen, dispose of old LCD responsibly; it contains mercury-free but nonetheless non-biodegradable materials.
Practical guidelines
Implementation steps for a professional repair shop:
Potential challenges
Possible disclaimers or additional notes
• If no drift in any measured voltage is found, assume COF failure; economical write-off for domestic repair.
• Pressing the bezel locally may momentarily clear stripes; this is not a fix and can crack the glass – do not recommend to end-users.
Suggestions for further research
Brief summary
Stripes that materialise 1–2 min after power-on in the Samsung UN48H4200AG almost always stem from the panel’s own driver electronics, specifically the VCOM/Gamma circuit or COF tabs, which drift when warm. Verify by measuring VCOM and performing selective cooling/heating; main board faults are highly unlikely. If VCOM IC or nearby caps are the culprit, skilled micro-soldering can solve the issue; otherwise the panel must be replaced.