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TV repair question

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  • Howard Chester
    Hello Stephan, most TV vertical drive circuits derive their supply from the line output transformer (LOPX) via a diode and fuse-able resistor of anywhere from
    Message 1 of 2 , Nov 1, 2010
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      Hello Stephan,
      most TV vertical drive circuits derive their supply from the line output transformer (LOPX) via a diode and fuse-able resistor of anywhere from 0.1 ohm to about 100 ohms. other than tracing the chip supply back to this resistor and checking for an open circuit is best.These "look" OK externally, but until metered out seem fine. As for the caps, replace all the electrolytic's near the chip, as if one has gone
      west, the rest are probably close to death's door anyway. And replace the cap on the supply line near the fuse resistor at the LOPX (go for a 105 deg high temperature type with low ESR). As for the chip, well until I've replaced the caps/resistors and powered up the circuit, I would'nt write it off. (a quick check, meter out the supply pin to ground at the chip...+-2K ohm should be expected)






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    • Stefan Trethan
      The chip should have supply, since I measured signals on several other pins. However I did not check the supply pin and will do that. There s a lot of stuff
      Message 2 of 2 , Nov 1, 2010
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        The chip should have supply, since I measured signals on several other
        pins. However I did not check the supply pin and will do that. There's
        a lot of stuff connected to the flyback transformer, which doesn't
        make so much sense if one isn't familiar with TV design.

        I'll change all the small can 'lytic capacitors in the bridge, there
        are only about 50, because half I tested were bad. They used the
        bridge pretty hard for a long time (switched on all day), so it is no
        surprise it is all dried out. I try to switch off equipment if I don't
        need it, not least because I might be the one taking it home when it
        is thrown out ;-).

        Thanks,

        ST

        On Mon, Nov 1, 2010 at 8:05 AM, Howard Chester <howard.chester@...> wrote:
        > Hello Stephan,
        > most TV vertical drive circuits derive their supply from the line output transformer (LOPX) via a diode and fuse-able resistor of anywhere from 0.1 ohm to about 100 ohms. other than tracing the chip supply back to this resistor and checking for an open circuit is best.These "look" OK externally, but until metered out seem fine. As for the caps, replace all the electrolytic's near the chip, as if one has gone
        >  west, the rest are probably close to death's door anyway. And replace the cap on the supply line near the fuse resistor at the LOPX (go for a 105 deg high temperature type with low ESR). As for the chip, well until I've replaced the caps/resistors and powered up the circuit, I would'nt write it off. (a quick check, meter out the supply pin to ground at the chip...+-2K ohm should be expected)
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