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Repair 74cm TV Power Supply

Smoothing Capacitor does not discharge and TV is dead. I measure 312DC Voltage across it even when Set is OFF.

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Hi there, check the bleder resistor, it was 100 kilo ohms or up, near the biggest capacitor at the power supply. do some test and check up. ty

Posted on Feb 16, 2008


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Posted on Jan 02, 2017


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How do I fix the touch buttons on Emerson TV model no le220em3? I have replaced the fuse and still have no power the buttons won't work there's no standby light and my universal remote does not work.

A replacement power supply may be hard to find, however, they are usually not that difficult for an experienced technician to repair. The most common failure is a burned-out electrolytic capacitor (sometimes several go bad before the TV quits working). Common symptoms of a failing capacitor are trouble starting the TV - it may take several tries before it goes on and stays on, and occasional spontaneous shutdown. It gets worse until the set quits completely. Burned out capacitors are often easy to identify; the top will be domed instead of flat, and black or brown material may have seeped out of the top. See the photo below for a comparison of bad capacitors (domed tops marked with red) and a good flat-topped capacitor.

The missing light suggests you may have a failed standby power supply section. This could be a shorted transistor leading to a blown fuse and possible damage to other parts. My usual sources list the power supply for your model as out of stock, but ShopJimmy has repair kits for some versions (see link below) with this problem. At $13, they are getting a substantial premium over the cost of parts from component suppliers, but you also get instructions on which parts to change and save the hassle of looking up and ordering each part. (Soldering skills and anti-static protection knowledge required.)

Emerson LE220EM3 TV Parts

Note: You can save some money on labor charges by removing the back of the TV. (Keep track of where the screws go; there may be several types, and check carefully around the connector jacks for screws. Any screw marked with a triangle or arrow must be removed to take off the back, but not all may be marked this way.) Be sure to unplug the TV and wait at least 30 minutes before working on it; the input power capacitor may be charged to power line voltage and can give a nasty shock unless given time to discharge, especially if the circuit it feeds is disconnected by a blown fuse. Inspect the power supply for burned out capacitors, and compare the labels on the power supply with the numbers shown on the page linked above. If you have a digital multimeter, set it to 200 VDC and measure the voltage across Fuse F601. If you measure any voltage, the fuse is definitely blown. Don't replace it until the board is repaired (see the video in the link provided). If you don't measure any voltage, confirm the condition of the fuse by switching to the 200 Ohm range. A good fuse will read near zero Ohms, about the same as you would get touching the meter leads together. A bad fuse will read higher (the voltage measurement is to make sure you don't damage the meter by trying to measure the resistance of a part with voltage on it). If the fuse is blown, you probably need at least some of the parts in the repair kit. All of the parts in the kit except the resistor and fuse must be oriented the same way as the original; putting them in backwards can cause severe damage to the board. Prior electronic soldering experience is very highly recommended before attempting this repair yourself.

If you remove the power supply, be sure to handle the board only by the edges; do not touch any of the circuitry. Any static electricity charge on your fingers can damage the board, even if you don't feel a spark. Do not put it on or in any plastic bag or wrapper unless you know the bag is anti-static. If you must park the board somewhere, put it component side down so static buildup on the surface doesn't zap the circuitry.

Dec 16, 2016 | Emerson Televison & Video

5 Answers


Power supply troubleshouting:
(Some experience in electronics repairs and measurements needed)
remove the TV back.
Locate the big mains smoothing capacitor (near the mains input usually) its often 40uf-220uf 400v on 240v mains.
Switch on and test the voltage across this capacitor and expect 300volts or more (320v average uk) or 1.414 times the mains RMS voltage
07d6466.jpg If 300v is ok at the mains smoothing capacitor
then check to see if 300v is reaching the chopper transistor
(middle leg) and its not at the other two legs.
If 300v is ok at the mains smoothing capacitor
then check to see if 300v is reaching the chopper transistor
(middle leg) and its not at the other two legs.
d6fc2da.gif now check the output from the chopper transformer it will usually have at least 2 outputs
one is HT ,about 95v to 115v for 14" to 115 to 150v 28" screen and the other LT will be about 10v to 20v
if HT very low then check for shorts across loptr or tripped crowbar
if 30v to 70v then use wire link to short out the base /emitter of the loptr, if voltage rises then loptx is probably gone.

Jun 30, 2008 | Sony Grand WEGA KDF-60XBR950 60" Rear...

1 Answer

Tv is dark with a horizental white gong thru the middle

Check the smoothing capacitor connected to the +B voltage line, at the main power supply output voltage. It will be an electrolytic capacitor, usually come to a capacitance value between 100MFD 160VDC to 220MFD 160VDC. You're seeing the supply HUM by the screen. Products powered by electricity should be serviced or repaired only by experienced professional technicians. Any attempt to service or repair the product by anyone else could result in serious injury or death. If you are not familiar with electronics, do not attempt to repair.Whether you suffer fatal electrical shock.Instead, contact the nearest service centre. To get some details, up older posts.

Dec 04, 2013 | Toshiba 36A10 36" TV

1 Answer

Lines and distortion across screen

Check and replace the smoothing capacitor used at it video output voltage This capacitor can be located at the neck board of picture tube.To get more details, Pull up older posts.

Nov 29, 2013 | Philips Magnavox 20MT133S 20" TV

1 Answer

Too much Brightness

Check its video output supply voltage. If it is less than normal, this kind or fault can occur. Check the smoothing capacitor used there to smooth this voltage. Replace it. These components can be located at the video output card, which is plugged directly to the back of the picture tube.

Nov 11, 2013 | LG 30FS1D TV

1 Answer

Sylvania tv shrinks the sides

Check its secondary power supply voltage from SMPS power supply. Check the smoothing capacitor connected to secondary power supply voltage, replace it.

Jun 13, 2012 | Sylvania 6420FB 20" TV

1 Answer

I have RED verticle lines all the way across the screen fro top to bottom 10 minutes after I turn my Panasonic PT-52LCX65 TV on. Is there a solution?

Check and replace the main filter capacitor in the power supply section. Replace all of them in the secondary section of the power supply too. The problem is due to insufficant smoothing and regulatio fo the power supply section. If main smoothing capacitor gets value deveoped, it won't supply enough voltage to the switching section, and switching section also will go inefficient. Replace all of them. It won't cost not much. OK.

Jun 22, 2011 | Panasonic PT-52LCX65 44" HDTV

1 Answer

The picture does not come on when I turn it on.


Your TV is now in dead condition I should say. You should strart from its power supply regulation section itsef to rectify the fault. Look into the fuse, a glass fuse is there, in power supply board. If It has found blown, make sure that there is something short in either power supply regulator side, of on the other part of the printed circuit board.
You just place a fuse of same rating as used, if the fuse is blown. If the fule you installed newly also blows off, check first the retifier stalk for any leak. The stalk contains four diodes, even any one of them gets shorte, fule will blow up. If there is no leak in the retifier stalk, measure the voltage resistance across the main filter capacitor, a bulky one capacitor fitted in the power regulator section. If you see a full deflection on meter, it means that there is some dead short inside the power regualtor system.
Usually Sony uses STR regulated type power supplies, and some uses MOSFET [Metal Oxide Semiconductor Field Effect Transistors], as switching elements. Bothe of these types can be shorted, due to a high voltage spikes, or a sudden supply failure and restart.
Check out short test on these components, out of board, that is, desolder it out from the circuit board. You just resolder one by one and measure the resistance ad described above. Thus you can find out the exact component, that have a short. If any of these components shorted, check the entire power regulator section for any more component failure, like zener diode short, resistors opened, and so on. You should have a concept of soldering and a little knoledge in electronics. There will be a MOV [Metal Oxide Varistor] fitted across the power supply input, which look like a disc capacitor. it will get shorted when a certain voltage spike occures abvve its rated voltage, and apply a dead short at the supply stage. If any of them used, desolder it out and check for any leak, and is found leaky, replace it. It is used as a saftey measure, and without it the set will work fine.
Just check these and if you find any difficulty, contact me through Fixya. Ok.

Nov 29, 2010 | Sony KV-36XBR450 36" TV

1 Answer

Several lines run across the top of the screen

Several lines acroos the screen at the top along with picture is a typical fault. You are seeing vertical retrace lines. Either the supply smoothing capacitor to the power supply given to vertical output Ic or vertical output capacitor connected to the vertical output pin of that Ic may faulty. Usually the supply smoothing capacitor seen faulty. It may be over 1500Mfd eletrolytic capacitor used there. It may get value reduced by 40 percent or so, this falult will occur. Please replace the two capacitors together and will get the result.

Oct 15, 2010 | Toshiba 27A34 27" TV

1 Answer

Dead power supply power across the bridge 700 volts across the main capacitor indicating smps is filtering

sounds like you have a dead switching suppy. On these sets the best way to trouble shoot the power suppy is disconnect the horizontsl output and measure it Is it shorted yes replace the fly and the transistor and resolder several cold joints in the horizontal drive curcuit as well as in the main switching supply. If the HOT not shorted then your gonna need a service manual unless you shotgun the repair. Good Luck

Apr 18, 2006 | HP Pavilion M703c 17 in.CRT Conventional...

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