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Power surge or electrical outage tv blue light stays on with humming sound no picture

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Hello,

Power surges or nearby lightning strikes can destroy electronic equipment. However, most of the time, damage is minimal or at least easily repaired. With a direct hit, you may not recognize what is left of it!Ideally, electronic equipment should be unplugged (both AC line and phone line!) during electrical storms if possible. Modern TVs, VCRs, microwave ovens, and even stereo equipment is particularly susceptible to lightning and surge damage because some parts of the circuitry are always alive and therefore have a connection to the AC line. Telephones, modems, and faxes are directly connected to the phone lines. Better designs include filtering and surge suppression components built in. With a near-miss, the only thing that may happen is for the internal fuse to blow or for the microcontroller to go bonkers and just require power cycling. There is no possible protection against a direct strike. However, devices with power switches that totally break the line connection are more robust since it takes much more voltage to jump the gap in the switch than to fry electronic parts. Monitors and TVs may also have their CRTs magnetized due to the electromagnetic fields associated with a lightning strike - similar but on a smaller scale to the EMP of a nuclear detonation.
Was the TV operating or on standby at the time? If it was switched off using an actual power switch (not a logic pushbutton or the remote control), then either a component in front of the switch has blown, the surge was enough to jump the gap between the switch contacts, or it was just a coincidence (yeh, right).
If the TV was operating or on standby or has no actual power switch, then a number of parts could be fried.
TVs usually have their own internal surge protection devices like MOVs (Metal Oxide Varistors) after the fuse. So it is possible that all that is wrong is that the line fuse has blown. Remove the cover (unplug it first!) and start at the line cord. If you find a blown fuse, remove it and measure across the in-board side of fuse holder and the other (should be the neutral) side of the line. The ohmmeter reading should be fairly high - well certainly not less than 100 ohms - in at least one direction. You may need to unplug the degaussing coil to get a reasonable reading as its resistance may be 25 or 30 ohms. If the reading is really low, there are other problems. If the resistance checks out, replace the fuse and try powering the TV. There will be 3 possibilities:

  1. It will work fine, problem solved.
  2. It will immediately blow the fuse. This means there is at least one component shorted - possibilities include an MOV, line rectifiers, main filter cap, regulator transistor, horizontal output transistor, etc. You will need to check with your ohmmeter for shorted semiconductors. Remove any that are suspect and see of the fuse now survives (use the series light bulb to cut your losses
  3. It will not work properly or appear dead. This could mean there are open fusable resistors other defective parts in the power supply or elsewhere. In this case further testing will be required and at some point you may need the schematic
hope this helpout......

Posted on Jul 08, 2010

  • 1 more comment 
  • Sanyade Akinwale
    Sanyade Akinwale Jul 08, 2010

    ALSO NOTE THAT

    The most likely cause is a dried up main filter capacitor. Once the effective capacitance drops low enough, 120 Hz (or 100 Hz in countries with 50 Hz power) ripple will make its way into the regulated DC supply (assuming full wave rectification).Another likely cause of similar symptoms is a defective low voltage regulator allowing excessive ripple. The regulator IC could be bad or filter capacitor following the IC could be dried up.
    Either of these faults may cause:


    1. A pair of wiggles and/or hum bars in the picture which will float up the screen. For NTSC where the power line is 60 Hz but the frame rate is 59.94 Hz, it will take about 8 seconds for each bar to pass a given point on the screen. (On some sets, a half wave recitifier is used resulting in a single wiggle or hum bar).

    2. Hum in the sound. This may or may not be noticeable with the volume turned down.

    3. Possible regulation problems resulting in HV or total shutdown or power cycling on and off.
    The best approach to testing the capacitors is to clip a good capacitor of approximately the same uF rating and at least the same voltage rating across the suspect capacitor (with the power off). A capacitor meter can also be used but the capacitor may need to be removed from the circuit.
    Once the capacitors have been confirmed to be good, voltage measurements on the regulator should be able to narrow down the problem to a bad IC or other component.

    Good luck.,,,,,,



  • osevgi Jul 08, 2010

    tv was off during power outage the fuse looks ok whats next

  • Sanyade Akinwale
    Sanyade Akinwale Jul 09, 2010

    Hello,
    Check on bulged capacitors , if found replace with the same rating voltages..Also check fuses resistors, that is these are fuses but physcially looks like resistors. if otherwise , you can try websites Shopjimmy.com,Ebay.com to buy a refurbish power supply board for the replacement.

    thanks for your comments , let me know the outcome... take care


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Hi. There is a safety fuse in the tv which will blow in order to protect the more expensive components of the tv. If you are not into electronics, do not have the necessary meters and tools, take the tv to a repair shop to save the cost of a house call. J.

Posted on Jul 09, 2010

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First off what is the make and model of the tv, and how long have you owned it. Once I have more information I can assist you further.
Thank you,
Lee

Posted on Jul 09, 2010

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