Philips model 46pfl3706/f7 television

[Cdm1212]

Hi,


I am attempting to repair my television. When I turn it on, it seems to start normally and then the backlight turns off after a couple seconds.

Initially on the main power board I replaced diode D1202 which was shorted, and capacitor C1201 which was bulging. I was still getting some wonky voltages, so also replaced C1204, C1250 on the main board, as well as the filter caps on the LCD module, which were 3 680uf caps in parallel, which I replaced with 2 1000uf caps in parallel.

The tv is still showing the same symptoms, although now I am getting decent voltages (within 0.5 volts) on all connections to the main board EXCEPT for pin 13 backlight adjust pin on the LCD module assembly, which shows reading 0v on the schematic, but in reality it reads 3v DC.

Service manual attached, (though it doesn't seem there is a schematic of the LCD board, Samsung part # ss1460_08a01 Rev 2.0

Any help or direction would be greatly appreciated. Thanks in advance.

[nomoresonys]

Post good clear straight on pictures of each board and one of the whole back as to see how everything is connected, make sure all the solder joints are good on bottom of powerboard, can search images of bad solder joints if needed.

[Cdm1212]

Thanks for replying.

Here's requested pics.

I did go through the main board with a magnifying glass and nothing really jumped out at me, but maybe I missed something, I can check again. Looks like there are a few components that maybe got warm.

Looking at the main digital board possible the main 470uf capacitors are bulging a bit? Not really familiar with surface mount electrolytics.

[nomoresonys]

Ok, here's a little test that can sometimes sniff out a bad/marginal capacitor, heat the electrolytic caps on the powerboard up with a hairdryer for a couple minutes, then try tv while it's still hot, see if it stays on any longer.

[nomoresonys]

Test all the diodes and resistors on top of powerboard for starters, youtube is your friend for how to videos if needed, you did check all the solder joints on bottom of powerboard right.

[Cdm1212]

Hi, thanks. Yes, I went through the main board and resoldered anything that looked suspicious, although nothing really jumped out at me.

I did test all diodes and resistors, as well as the transistors, they seemed to be working as intended. A couple tested strange in circuit, but I lifted a leg and they seemed ok.

I tried heating up some of the capacitors, and had no luck with lengthening the time the backlight stayed on. Is this the type of problem that can be caused with faulty caps? It wouldn't bother me to order new ones and basically redo the whole lot, if there was a high probability that could solve the issue. Some of the smoothing capacitors don't really test well for resistance across them, testing in Kohms rather than Mohms. On the other hand, if this seems like more of a IC problem or something, I'd probably just salvage some parts and get another TV. I am pretty stubborn to admit failure though.

[nomoresonys]

Maybe check the transistors and the little ceramic caps on the inverter board for shorts or very low ohms. I suppose the fuse on inverter is ok or it probably wouldn't even come on for a few seconds like it does.

[nomoresonys]

Being an older tv, it's probably not a bad idea to replace all the electrolytic caps, it would rule them out at least.