Phillips Magnavox 42MF438B/F7 does not power up

[mike123333]

Re: Phillips Magnavox 42MF438B/F7 does not power up

Which caps would you recommend to change . I did replace the 2 caps on the secondary side of the transformer for the 3.3V but that did not do it. I was talking to the individual that gave me the TV.. He stated that he lost another TV with this power outage he had at the house to the point that the main switch ( usually thsi does not happen) to the panel kicked off... having said that he did state his wife heard a pop in the TV then the power went out..

To take out the rectifier and mosfet and destroy a copper trace the board seen a nice dosage of amerage.

[budm]

Re: Phillips Magnavox 42MF438B/F7 does not power up

The whole thing still does not make sense yet, we load down the power supply with 5 ohms and it still putting out 3.3V OK. The spec on the board shows the 3.3V with output current rating of 200mA, we loaded with 600mA and it is OK, but when you have main board connected, the voltage goes down. I am not really sure what is going on and we still have the 12/24V power supply problem in that section as well.

[mike123333]

Re: Phillips Magnavox 42MF438B/F7 does not power up

I more doing more voltage troubleshooting at the primary side of the 3.3v tranformer. The main bridge rectifier does not supply the DC voltage to the 3.3V primary side of the the transformer that is a seperate circuitry which is on when teh board is powered. The voltage is at 168-169VDC. also I have noticed on the primary side of the transformer another voltage of about 16-18VDC. that voltage is dropped out upon the main board being hooked up and the PS is momentarily turned on. There is a 47UF 50v elect capacitor upon measuring the voltage across either the diode or capacitor it is reduced to below 1 VDC. whether this is an issue or not I am not sure.

On the power supply board in the photos I previosuly posted the diode would be D107 and capacitor C121. Unfortunately I do not have a cap in that size to replace for testing. the resistor between the diode and capcitor has 168VDC on 1 side and the other side is the 16-18V.

In addition, one of the legs of PC101 will have this 16-18VDC HOT Side and the cold side is the 3.3VDC but when it drops out the 3.3VDC goes to almost 0...BTW what is the PC102 and PC101 used for....

Sorry for being long winded but I wanted to capture some of the obseravtions I made.

[budm]

Re: Phillips Magnavox 42MF438B/F7 does not power up

That is the start-up cap, you can try replacing that cap, it is one of the common failure cap in switching power supply.
Can I see the picture of this PCxx? I think they are Opto couple, they use Opto couple to provide the feedback from the output side which is isolated from the hot primary side. It is power by the output, so if the out go down, there will be no voltage to turn on the Opto.

[mike123333]

Re: Phillips Magnavox 42MF438B/F7 does not power up

I took a top and bottom picture view of th opto.

[mike123333]

Re: Phillips Magnavox 42MF438B/F7 does not power up

I have exchanged some caps around that 3.3v primary side from te egood board and new ones if I had them available nothing seemed to change anything. I even exchanged the Quasi-Resonant Converter U101 FSQ510 near the opto coupler on the primary side with similar results .

I ll post up soem voltage readings of the comparison between the PS. I did notice a loss or drop of voltage across one resistor which I cannot find the rootcause this is of course when the main is connected. I wihs I had a schematic to go by its diifficult troubleshooting by following traces.

[budm]

Re: Phillips Magnavox 42MF438B/F7 does not power up

Boy, you are BRAVE to take the parts from good board and install in the bad board. Yes, I wish we have the diagram to really test section by section.
That is good idea to take voltage readings of both board for comparison, I was going to suggest that but I am afraid if you slip the probes and take out the new board.

[mike123333]

Re: Phillips Magnavox 42MF438B/F7 does not power up

I attached the photos of the top and bottom view of the primary side of the 3.3v along with voltage readings at some locations. One of the things I see is the massage drop in voltage across the R104.I did switch out the U101. Let me knwo your thoughts.

[mike123333]

Re: Phillips Magnavox 42MF438B/F7 does not power up

I thought the power supply was the only problem..a put everything back together and fired right up everything went smoothly upon completion of auto programming. picture is good but no sound..the first thing on my mind was did I plug the speaker harness back into the Main, so after removing 30+ screws the wire harness was plugged. I probed around and looked up the specs on the AMP there was no voltage being delivers to the speakers. The VCC on all 4 legs were active but no output. I pulled my hot air station out and decide to remove the chip. This is the second time I have experienced where the bottom padding was literally on there for good. I literally burnt my hands holding the board down. I decided to forgo the hot air and went with the iron even that was not chore. The part is on order and we will see what net affect.

The chip was so hot I could not place my finger on it when I was testing it out for shorts. That high temp in itself caused me to dig further into it.

The TV is being sold in several days...Hopefully there is a happy ending to this endeavor.

[budm]

Re: Phillips Magnavox 42MF438B/F7 does not power up

On the user setup menu, is there a function to turn off the internal speakers so when you use it with the surround sound system (using Audio Line outputs) there will be no sound coming from the V speakers?

[mike123333]

Re: Phillips Magnavox 42MF438B/F7 does not power up

before i took everything apart and removed the chip, I went through the obvious and made sure the speakers were not turned off or muted and the setup was fine. I was using the cable instead of any other source.

[kuyote]

Re: Phillips Magnavox 42MF438B/F7 does not power up

I know this is a very old post. But was hoping age of you might still have these Tvs. I have the same TV and thought it was bad caps. But after replacing them, still nothing. Looking closer, the fsq510 ic is fried. Possibly the diode next to it. I can find the ic, but can anyone tell me what the diode is in d107?