A customer recently booked her Samsung TV in for repair with us, saying it was clicking, and not actually coming on. I’ve had this problem with an old Toshiba plasma of Kana’s over at White Tiger Martial Arts Academy, it was clicking badly, but actually worked, with visible distortion on dark scenes. In that case though, it turned out to be the plasma panel itself stressing the supply, as we couldn’t source a panel at less cost than the TV it had to be written off.

LCD’s though are much easier to source, and will never actually stress a high voltage supply as they themselves only run at 5v DC on their LVDS bus, so once we’d picked the customer’s TV up from her house, we took off its cover, and took a look. It turned out to be one of our most common problems: Bulging capacitors! Except these were high quality Korean Sanhwa ones. Once you get the cover off (just 12 screws, no plastic clips unlike Vestels!) you’ll see the PSU on the chassis. It uses a massive flyback transformer and opto-isolator for SMPS feedback, to power the backlights. If you thought flyback transformers died with CRT’s, you were wrong!

Samsung LA40R81BD-PSU-removal

Follow this procedure to remove the supply:

CAUTION: WAIT at least 30 minutes if the TV has been plugged in. If you are experienced in electronics you can discharge the main filter capacitor using a resistor, if not, leave it unplugged for a while before continuing, and have a brew, thinking about how you’ll proceed, and make notes. I find cuppa-plan time to be very productive, and it keeps me safe, even as a professional. There are high voltages present that can KILL!

1. Remove all connectors I’ve coloured GREEN. They have tabs on them which you must push as you pull the connector. DO NOT pull them out by the wires, you’ll rip the socket off the board and damage the socket pins, making this cheap repair much more expensive.

2. Unscrew and remove all screws I’ve coloured RED, and put them somewhere safe. Remove the board by lifting it by its EDGES, not by a transformer or capacitor, or any other component. Place the board on a suitable workspace, with plenty of room, and an antistatic mat. SMPS supplies contain surface mount components and controllers which are easily damaged. Simply walking on a carpet generates 70,000V which we can only feel as a slight shock as there’s hardly any amps, but that is more than enough to wipe semiconductors out!

Samsung LA40R81BD PSU capacitors

3. You’ll notice near CN801 there’s a bunch of capacitors, and some of them will likely be bulged, or have actually vented. If any vents have burst, you must clean the electrolyte off as soon as possible, as it’s corrosive to the board and other components. I generally replace all output caps if any have become damaged, as they will have been stressed. On my board there were 2ea 2200uf capacitors that were bulging. Remove the old capacitors ensuring you don’t overheat or damage the copper pads/tracks on the circuit board.

CAUTION: Take care to ensure you install the new capacitors correctly. They are polarity sensitive. The board and capacitors will be clearly marked which way they should be inserted. Shorted or polarity-reversed capaitors can EXPLODE and/or damage other parts of the circuit.

You should check and if necessary replace any adjacent capacitors that are rated 10V as these seem to be the ones more likely to fail. In my case I also replaced the 1000uF capacitor. Capacitors, contrary to misconception do not have to look visibly damaged to be faulty, they can be internally dried out.

NOTE: If replacing the capacitors does not resolve your symptoms you may need to replace the EEPROM chip on the main board as it can be corrupted or damaged by the power cycling. This will need to be done by a professional as the software contained in it can be TV specific.

 

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