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HomeG Board or N Board I have a Sony Big Screen that I got for free from a relative. His house got struck by lightning and the tv no longer turns on. There is no standby light or anything when the set is plugged in. All fuses are good. I found a couple of shorted diodes on the G board and replaced. I also replaced the varisitor. The model of the tv is KP-46XBR35. The only thing it does is make a high pitched sound for a second and stops from the 2 200v 820uf capacitors(biggest ones on the G board). There are 2 relays on this board and they only work for a second when the set is plugged in, making the sound from the caps. I could tell someone been through this board before because 2 transistors (Q603,Q614)and 1 diode(D605)were unsoldered from it. I ordered them from Sony plus a couple of IC's and a zener diode that connects to D605(was open) and still no luck. Would something on the N Board be fried from the lightining strike to make the tv not turn on? I'm new to TV repair and it would be nice to have a 46" tv instead of a 27". I just got the service manual for it so part numbers is not a problem to get. But actually finding another G or N board is the hard part. Believe me, I already looked. They are both unavailable from Sony. So I have to fix what I have. Help!!!
1 comment
Jason, I have good experience with Sony and other brands of monitors, but not TV's. However, the concept is all the same for switching power supplies. You have a switching transistor or IC that chops the incoming DC to switch the transformer. The complicated part is the feedback that goes on. If ANYTHING is wrong in the secondaries, the power supply will not start up. Since you have a service manual, you are ahead of the game. Even better if a schematic is included. Anyway, I would first look in the high voltage section. Particularly a shorted HOT (Horizontal Output Transistor). Next, I would look at every secondary side component of the power supply transformer, especially the diodes. Take your DVM and check for shorts or low ohm's on each of the DC lines. Except for the 6 volt line for the CRT heater, they should all be at least 100 ohms or so. If you hadn't done so already, use the scope to check the waveform's of the primary side and secondary side. The switching transistor or IC is also a common failure. Another approach would be to isolate the secondaries one at a time by lifting the diode to see if the squealing goes away and if the power supply turns on. PS - if you find a bad common part, save yourself good money by ordering from mail order electronic companies; like MCM Electronics or Digi-Key or Active Elctronics. Or maybe you have local places that sell ECG equivalents. If parts are common, you don't have to go to Sony and spend twice as much (or more). |
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