Model LN40B500 LN40B500P3F LN40B500P3FXZA

When turned on, the backlight would come on for a second, turn off and this would repeat for a couple of times. Power supply part number is BN44-00264A. Schematic is available online. This badcaps thread indicates potentially bad transfomers on the inverter or bad ccfl bulbs in the backlight. I hooked probes to the main filter cap to monitor the PFC voltage and it was steady around 390VDC throughout. The thread indicates to connect a wire to pin 10 of the UI801 to see if the overvoltage protection was being triggered from faulty bulbs. This signal was high when the backlights were on confirming the fault. The thread also mention to bypass CI805 on pin 2 which should keep the backlight from shutting off. This modification worked as well. I put a plain white image on the screen and could verify a few bulbs were dim and triggering a fault.

Since the LCD TVs are becoming old and obsolete, I decided to scrap the TV and was able to use the main board on a LN46B500 TV I had.

Model LN46B500 LN46B500P3F LN46B500P3FXZA

This TV had a standby light but didn’t turn on. With the main cable unplugged from the power supply, the backlights turned on. The main suspect in this scenario is the main board. Searching for the part BN94-02746Z on ebay yielded some expensive boards and an eeprom from Shopjimmy. I tried freezing the eeprom but the TV didn’t start but I bought a new eeprom anyway. After installation, it still didn’t work. Shopjimmy indicated BN94-02746L was a substitute part but I couldn’t find either at a reasonable price. Searching without a suffix showed BN94-02746Y from LN40B500 may work since the board picture matched but again there weren’t any reasonably priced boards on ebay.

Putting the TV aside, I was able to get a LN40B500P3F with backlight issues and a BN94-02746Y main board. Plugging it into the 46 inch model worked. A second LN40B500 substitute is BN94-02746K.

I proactively replaced four electrolytic capacitors on the power supply board BN44-00265A.

CM858, CM859 – 1000uF/25V
CM852, CM853 – 1000uF/10V

This TV turned on with no backlight. Google indicates this model suffers from backlight failures but replacement LED strips are not readily available. This set is configured as two strings of LEDs and one open LED was found. It was repaired with a 3V Samsung compatible LED module.

Backlight level can only be adjusted in the service menu under Panel Settings. With the tv on, menu-1-1-4-7. Vivid mode sets the backlight to 100%, Standard is 85%, and Energy Saving 50%. You should keep the TV in Energy Saving mode or adjust Standard mode to 65% which gets saved as User mode. You will need to make this adjustment for all inputs.

Model UN50F6300 UN50F6300AF UN50F6300AFXZA UN50F6300AFXZC

This TV turned on with backlight but no video. Normally in this scenario, the tcon board is suspect. I disconnected the ribbon cables from the tcon to the panel one side at a time and got a good picture on the right side. This test indicates there is a panel fault on the left side. I checked the panel board on the left side for shorts on the chip capacitors but didn’t find any. I next used the the tape cutoff method to block pins on the ribbon of the left side connector on the leftmost side (outer edge). The initial attempt blocking 2-3 pins didn’t work so I used a wider strip. With 5-6 pins blocked, the TV turned on.

LED backlight failure is common in all LED TVs. With Sharp and RCA Roku TVs, turning down the backlight level isn’t very intuitive.

1. Under Settings-> TV Picture Settings Set the TV Brightness to Normal. It defaults to Brightest I’m not sure if this is controlling image brightness or backlight level but safer to set it to Normal.
2. With your current input selected (eg HDMI 1), hit * on the remote. Go to Advanced Picture Settings. Set Picture Mode to Low Power, Dynamic Contrast to Off and the Backlight to 60-70. The lower you can tolerate the better. The default for low power is 78 which still seems high. Most picture modes set the backlight at max which will burn out the LEDs.
3. Repeat step 2 for all inputs you are using and also check all apps (eg. Netflix, Roku media player you are running.

I was doing a led replacement for a UN40H6203AF and ordered replacement strips, but the middle strip didn’t match. These series of Samsung LED TV’s use 3 strips with 2 angled strips and a middle straight strip. Part number is LM41-00001V for the angled ones and LM41-00001W for the straight one. When I installed the straight strip, the holes didn’t match. I noticed there were 12 leds on the strip and I needed 13. Though the angled strips were the same part number, the straight strip was different.

For the 13 led straight strip, the part number is D3GE-400-SMB-R3

I don’t see a lot of LCD TVs anymore since they are getting old and obsolete. This one had almost all the 2200uF/10V capacitors bulged. I proactively replaced the 470uF ones as well.

C221, C206, C217, C202, C215 – 2200uF/10V
C222, C226 – 470uF/25V
C203 – 2200uF/25V
C210 – 1500uF/35V

Update: I encountered another 32LC7D with one bulged cap but the backlight did not come on. Backlight control comes from the pin labelled I-C and there was no high signal from the main board so I replaced the board. The capacitors on this board were also replaced.

C207 – 1000uF/35V
C212 – 2200uF/25V
C203, C208 – 470uF/35V (one is actually 25V)
C215, C225 – 2200uF/10V
C204, C205 – 3300uF/10V
C221, C222, C223, C232 – 680uF/35V

This 2 year old TV had a blue and purple tint and the backlights were suspected of turning blue. Removing the panel confirmed this colour change happened. Shopjimmy only shows one set of backlights for this model but they didn’t match what was in my tv. Shopjimmy part is 3 rows of left and right strips with 9 LEDs per row and labelled 49UJ65 for panel HC490DGG-ABSR2. My TV has a LC490DGG panel and strips are marked V17 ART3 and there are two rows of 12 LEDs per row.

List of models that use the same style of LED.

• Hisense 55H5C (strips SVH550AH9 or SVH550AC3) also 55H6B, Insignia NS-55D510NA17 Sharp LC-55LB481U LC-55LB481C
• LG 43UH6100 43UH610A 43UJ6300 43LJ5500 43 inch models have at least two styles of strips (three long strips) one with 7 leds and another with 8 so be careful ordering replacements
• Philips 43PFL4902/F7
• Sony XBR-49X700D XBR-55X810C KD-60X690E XBR-65X810C
• Toshiba 50L711U18 55L711U18
• Vizio D58U-D3 E65U-D3 D650i-B2

Update: I popped off the lens to investigate and it appears these LEDs are naturally blue but are covered in a yellow filter. The yellow filter has cracked and crumbled away.

Update – Looks like this problem is also affecting LED street lighting.

Why are street lights turning purple? News 40 investigates – News 40 | WNKY Television

UN65MU6290VXZA UN65MU6290VXZC

I researched this model thinking I could repair it since I had salvaged parts from a cracked screen TV. Apparently, there are two different versions. UN65MU6290F and UN65MU6290V. The V version is edge lit and is very prone to backlight failure. Shopjimmy recommends replacing two resistors to limit the backlight current after LED replacement. This ebay post from a backlight seller indicates bad LEDs can damage the power supply and bad power supplies can damage the LEDs.

“On this model most of time one led strip and power board fail at the same time, to fix this issue you must replace that failed led strip plus power board. If you install this LED strip with failed power board and turn the TV on, LED strip will fail on the spot, also if you install a good power board with bad LED strips the same thing would happen to that power board. “

This ebay listing indicates the LED driver IC IC9101 SEM4082A can fail as well as Q101c and Q201c.

On top of all these potential issues, the back cover is screwless and needs to be pried apart. There are holes at the bottom to insert a tool to start prying apart.

This LCD tv turned on but without a backlight. Googling found a repair kit for transistors on the inverter board.

Testing the transistors on the inverter board, I found Q103 (Nikos P4004ED PCH, 40V, 21A) shorted and F101 (240V, 7A) blown. Replacing both parts restored the backlight. If Q105 or Q107 are shorted, the part is P2904BD (NCH, 40V, 25A).