Philips 42PFL3704D/F7 No pic,No Backlight, w/Audio

[ptepe]

When tv is plugged in, screen comes on with Philips logo and then screen turns off but front "on light" stays illuminated. I have 24 volts at inverter. Did test on inverter board and found that one of the two 8a/160 volt fuse which I believe is open because when conducting a test, 24 volts only reads on one side. I've enclosed a pic of the location of the fuse. When I jump the apparent blown fuse, plug the tv back in, tv clicks on but now no screen flash and then tv shuts off. When performing this test with volt meter, it seems to shut down all of the 24 volt power. When I leave the fuse open, the first result indicated above with 24 volts is present again. This tells me the power supply is working to the best of my knowledge. Does this tell me that the inverter board has a short? I checked the 4 caps on that side of the blown fuse and they're fine. Is it possible that there's a short in one or more of the transformers on the inverter? Any help would be fully appreciated.

[philliesfan30m]

Re: Philips 42PFL3704D/F7 No pic,No Backlight, w/Audio

yeah thats possible i would check the resistance on the primary and secondary sides of each inverter and compare results to see if you have any bad inverters. my guess is that it probably 1 of the inverters on the same side as the fuse that doesn't have the 24v on the other side of the fuse.

[budm]

Re: Philips 42PFL3704D/F7 No pic,No Backlight, w/Audio

There are 8 Power MOSFETs (black devices with metal tab on top) which drive the Inverter transformer that you need to check them for Source to Drain shorts.

[ptepe]

Re: Philips 42PFL3704D/F7 No pic,No Backlight, w/Audio

Thanks for the quick response. I did more checking and secondary side has 0 ohms. All transformers checked out fine.Narrowed it down to the two P2204nd5g shown in pic below. After removing which wasn't easy, the short subsided. Though taking these 2 transistors off, the few legs fell off damaging them. I see they're only available from china. I imagine this is common for the transistors to short but with the few legs that fell off when unsoldering, I was unable to test the transistors. Maybe better off ordering new board instead of messing around.

[budm]

Re: Philips 42PFL3704D/F7 No pic,No Backlight, w/Audio

To remove those MOSFET, you cut the two legs first, then add solder to the tab using 60W iron and twist the body of the MOSFET while applying the heat. I would order at least 8 of them, 2 already went out.

[ptepe]

Re: Philips 42PFL3704D/F7 No pic,No Backlight, w/Audio

Thanks BUDM. You must have been replying at the same time I was. You're absolutely correct. The two transistors I pointed out seem to have been the problem but unable to check do to the legs coming off. I was very careful but with the entire bottom of the transistor attached to the board with solder it was difficult to get off cleanly. I guess I'm just not patient enough.

[ptepe]

Re: Philips 42PFL3704D/F7 No pic,No Backlight, w/Audio

Unfortunately I did the opposite. I used my 60 watt iron thinking I could bend the transistor up and then remove each leg but that caused a few of the legs to come off. Great tip. I'll have to use that method next time.

[ptepe]

Re: Philips 42PFL3704D/F7 No pic,No Backlight, w/Audio

Ordered new inverter board for $50. TV works great. Thanks everyone.