LM317T Voltage Regulator with Pass Transistor

Picked up a M&S 20 inch TV from the garbage last week and since I was with a friend I lugged it home. It didn't turn on but I could hear the main relay clicking inside when I pushed the power button, so it was clear that there was standby voltage but no B+ This TV sports a very prehistoric power supply design, using a STR50103 linear voltage regulator with a honking power resistor in series in order to step down and regulate the incoming rectified and filtered line voltage. No transformer here. Turns out that a 470k 1/2 W resistor was open and the 130V protection diode was shorted and disconnected from the circuit, replacing the resistor got the TV working again but with a craptastic picture and the shaking you see in the video. The higher the brightness of the picture content, the stronger the shaking. Replacing a couple of electrolytic capacitors around the flyback area improved the picture considerably. As for the shakes, it turns out the regulator was defective, providing an excessive B+ of 125 V while the nominal value for this particular regulator is only 103 V. Needless to say, replacing the regulator got me a correct B+ and that stopped the shaking altogether. After adjusting the static convergence and the cathode levels I got a much improved picture, almost perfect from a TV that was salvaged from the scrap heap. I love electronic challenges like this one but I don't really need yet another TV set, so I gave this one to my mom after fixing it so that she can ...



http://www.youtube.com/watch?v=OvVqzpbYeUI&hl=en