This week I bought a Samsung Plasma TV, model number PN50B450B1D, for pretty cheap in a pawn shop. It was cheap because it had an issue where the image looked a little staticy all the time, even if there was no input source selected. The tag said that it didn't turn on immediately, and would shut off after 6 hours. This tells me the issue is thermal.
My background is in electrical engineering, and since this digital TV had analog noise all the time, I figured it was a bad capacitor. I jumped at the opportunity to have an easily fixable big tv for cheap.
I brought it home and took it apart, and to my chagrin, found no bulged caps. I put an o-scope on the power supply, and it looked clean, no noise. Both the x-main and y-main boards look fine too, however there's a buzzing coming from both x-main and y-main boards. The y-main board has buzzing near the transformer, so that might be normal, but the x-main has buzzing near a group of a few polypropylene film caps and a pair of TO-220 package transistors/diodes. The buzzing sounds like 60Hz, but I haven't put my scope on any components yet. As far as the possible thermal issue is concerned, all of the heatsinks on both x and y main boards were quite warm to the touch after the tv was only on for about 5 minutes.
My next idea is to replace all the caps, diodes, and transistors in the area of buzzing and see if it improves, but I'm having trouble matching the printed part numbers to actual components on digikey. I found one of the diodes I need, but nothing else.
Does anyone have any suggestions? Are there cap kits available for these boards? would that even fix the issue, or is it a bigger problem? Are there any specific tests I can run? As I mentioned, I already have a multimeter and o-scope (no capacitance meter, that's what I'd check next) I'd rather not buy new boards, since they're about $100 each. My boards' PBA numbers are LJ92-01688A and LJ92-01689A.
Images of my boards are attached. The picture of the red boxes is the area of buzzing on the x-main board, the red boxes appear to be polypropylene caps, and the diodes/transistors mounted on the heatsink to their left might be culprits too
Thank you all for your help
My background is in electrical engineering, and since this digital TV had analog noise all the time, I figured it was a bad capacitor. I jumped at the opportunity to have an easily fixable big tv for cheap.
I brought it home and took it apart, and to my chagrin, found no bulged caps. I put an o-scope on the power supply, and it looked clean, no noise. Both the x-main and y-main boards look fine too, however there's a buzzing coming from both x-main and y-main boards. The y-main board has buzzing near the transformer, so that might be normal, but the x-main has buzzing near a group of a few polypropylene film caps and a pair of TO-220 package transistors/diodes. The buzzing sounds like 60Hz, but I haven't put my scope on any components yet. As far as the possible thermal issue is concerned, all of the heatsinks on both x and y main boards were quite warm to the touch after the tv was only on for about 5 minutes.
My next idea is to replace all the caps, diodes, and transistors in the area of buzzing and see if it improves, but I'm having trouble matching the printed part numbers to actual components on digikey. I found one of the diodes I need, but nothing else.
Does anyone have any suggestions? Are there cap kits available for these boards? would that even fix the issue, or is it a bigger problem? Are there any specific tests I can run? As I mentioned, I already have a multimeter and o-scope (no capacitance meter, that's what I'd check next) I'd rather not buy new boards, since they're about $100 each. My boards' PBA numbers are LJ92-01688A and LJ92-01689A.
Images of my boards are attached. The picture of the red boxes is the area of buzzing on the x-main board, the red boxes appear to be polypropylene caps, and the diodes/transistors mounted on the heatsink to their left might be culprits too
Thank you all for your help
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