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#21 |
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#22 | |
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RCA Transistor.PNG |
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#23 | |
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So good to here you have it repaired. The red/green line is the R.F. channel indicator Last edited by R_J; 07-01-2022 at 08:49 PM.. |
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#24 |
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![]() Yes it is working. Thanks for your help. Much appreciated. It appears the whole problem was the wrong resistors. I was hoping you could explain how the transformer works. Is it upscaling or downscaling the power and is it converting DC to DC or DC to AC? I want to learn what was going on there.
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#25 |
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![]() In your case power supply is 12v. So to run backlight's and such the transformer is boosting voltage.
I'm confused. Resistors where bad? You then replaced with wrong value. Then put old ones back in, or new ones of correct value?
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I assume no responsibility for any stupid suggestions I might post. Last edited by dskall; 07-02-2022 at 11:20 AM.. |
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#26 |
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![]() wondering the same, I think he had a bad mosfet too.
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#27 | |
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The mosfet you replaced switches the raw 12volt input across the pimary of the transformer at about 50khz, this induces a current in the secondary windings of the transformer, there are likely 3 or more secondary supplies in this unit, one of them is a negative voltage whose diode is likely D303 and C323 is the filter cap. D306, D305, D302, likely supply other voltages for the tv. I suspect the mosfet shorted and you replaced it with a proper replacement, BUT you also replaced the source resistors at the same time. the values you used for those resistors were too high a value (2 10Ω in parallel=5Ω) The controller monitors the voltage drop across these resistors and was likely sensing a fault and shutting down. When you reinstalled the correct resistors (2 1.5Ω in parallel= 0.75Ω) the circuit operated as it should. The inverter circuit for the ccfl uses a different transformer (T401) and drive circuit Last edited by R_J; 07-02-2022 at 01:21 PM.. |
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#28 | |
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I think there is a separate transformer that runs the backlight power to the lcd screen. |
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#29 | |
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