Vertical range scan on TV not working

Discussion in 'General Electronics Chat' started by fastwalker, Sep 20, 2009.

  1. fastwalker

    Thread Starter Active Member

    Jun 24, 2009
    38
    0
    Hey Guys,

    Sorry for the slightly off topic post, but my TV just failed, the entire scan line is now on one horizontal line in the middle of the CRT. Is there any easy way to debug this without a circuit diagram? It's a Panasonic, about 8 years old, worked fine before this.

    Thanks,
    FW
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    You probably won't get far without a schematic. Do recall that TV's have lethal voltages present, so poking around inside an operating set can be dangerous.

    Vertical sweep collapse can come about from things like a bad resistor, a bad connection, a bad transistor, or a failed trigger circuit. If you're patient and have the test equipment, you may be able to check things like the voltage source and connections through the yoke as well as the associated transistor (unless the vertical driver is in an IC). But it's hard to do without the schematic.
     
  3. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    I don't know if they would still be in use at that time, but there was a very common vertical deflection IC, the TDA1170. These had distinctive solid tabs in place of the normal IC pins at the center of each side, often with add-on heatsinks soldered through the same slots as the IC tabs.

    They used to be a common failure problem in TVs and monitors, but also easy to replace and quite cheap.

    Keep an eye out for any electolytic caps with bulging tops or deformed (shrunk / short) insulating sleeves, all around the chip should really be changed.

    Data, just in case:
    http://www.datasheetcatalog.org/datasheets/400/378006_DS.pdf
     
  4. bertus

    Administrator

    Apr 5, 2008
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  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You can get a Sams Fotofact schematic for most TVs and many other appliances here:
    http://www.samswebsite.com/photofacts.html

    They are not free, but are really quite good.

    Just a schematic alone is not enough, however. You'll need more than a basic knowledge of electronics, and you may need tools like an oscilloscope, and know how to use them.

    TV sets that use cathode ray tubes have high voltages present inside the case, even if the set has been off for days.

    Unless you have at least a good basic knowledge of electronics, I strongly suggest you take your set to a TV repair shop.

    Frequently, a set that's past 7 years old isn't worth repairing anymore, particularly if it's had a lot of use. Fix one thing, and six months later something else breaks.
     
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