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Philips 37MF231D whistles...power supply or not?

 
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robo_geek
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PostPosted: Sat Nov 21, 2009 3:16 am    Post subject: Philips 37MF231D whistles...power supply or not? Reply with quote

TV works fine except:
1) Inductor on LCD controller is singing
2) Audio has very annoying whistle/whine.

So far:
Replaced electrolytic C2074 (bulged) on PSU board as well as C2081 and C2082 which are all on the output side of the PSU.

I've tested remaining caps with my cap tester, touched up solder connections, and tested pretty much all passive components on the PSU. I have not dug into the scaler board yet.

I swapped the inductor on the LCD controller that was singing, but the new part sings just as well.

I have the PSU schematic (Sams Photofacts). My next stop is to start looking more closely at some zener diodes near the failed cap and borrow an oscilloscope from a friend (or buy one on ebay)...so I can see some of the signals.

My guess is that the PSU is putting out a high frequency AC ripple that is finding it's way to the inductor on the LCD controller and also getting amplified thru the audio amplifier (on the scaler board)????

The LCD controller connects to the scaler board as well....

Am I barking up the wrong tree, or getting close?

question about 'missing parts':

On the schematic as well as the board, there are some 'optional' caps. For example there is C2075 which is a 100uF cap on the 24V leg of the supply; it's not there. Would it hurt to install this part? I assume at the factory they install these parts only if the PSU won't meet specifications otherwise?
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