Phillips Magnavox 42MF438B/F7 does not power up

[mike123333]

I recently aquired a Phillips Magnavox 42MF438B/F7 that presently does not power up. When I received the LCD TV it would blow the main board fuse. It appeared that the bridge rectifier and a mofset were blown. I managed to repalce both components and the fuse does not blow anymore. The only voltage I have going to the main board is the 3.3v. I do not have the 12v and 24v. the front LED does not light up no fucntion what so ever. I have been combing the board for any other compents that might have blown but nothign jumps out at me. All other fuses on the board are good.

Any input would be greatly appreciated. The chasis number is LC8.14LA

I attached photos of the PS board.

[retiredcaps]

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

The only voltage I have going to the main board is the 3.3v.

Strange. Normally most electronics use 5V for standby voltage. Is 5V standby present on the power board and the main board?

[mike123333]

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

The PS only has 3.3v, 12v, and 24v...the 3.3v exists without the board going to the attached main board. I believe from there the relay switches and energizes the other components.

I don't have an esr meter to check the capacitors, they do not appear to have issues physically.

what is the best way of checking the tranformers and mofsets when energized?

[selldoor]

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

Pictures are not really clear enough for trouble shooting
can you get them a bit sharper - good light is the key.
Need pics of the main board as well.
On this board top left in your picture there is a half hidden orange component - is it a fuse? does the board designator begin with an F.

Please can you also update your profile with Country and Mains Voltage

[mike123333]

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

I will get better photos. I was using my iphone for quick photos. As for the orange component it is a fuse. when measured checks out good.

[mike123333]

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

Hopefully these photos will help. Thanks!

[tom66]

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

Okay there is a pin marked "Standby" on the PSU. With boards installed in TV and everything connected up what does this read?

[selldoor]

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

Busy day tomorrow so off to bed- have just to say im blown away with that first picture. Dont need to check the fuse its so clear we can see the wire. - fantastic

[mike123333]

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

with all the components attached to the PS the standby voltage is 0.000V DC.
With nothing on the board the voltage measures 2.655V DC

[mike123333]

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

Selldoor - I am not following you...which wire are you referring to??

[retiredcaps]

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

Selldoor - I am not following you...which wire are you referring to??

He is just complementing you on the pictures. They are so clear and focused you can see the fuse filament wire intact through the glass casing.

The regulars, only a handful of volunteers, see about 90% of the pictures posted here either with one of the following characteristics

i) out of focus
ii) posted inline (which irritates me)
iii) posted offsite (which also irritates me)
iv) poor composition
v) or uses someone's photos

Only 10% of the pictures posted are clear enough for our requirements to do remote troubleshooting.

[mike123333]

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

Ayone have any suggestions as to what I check? still troubleshooting but coming up with nothing.

[tom66]

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

So when you unplug the main board power connector, STBY pin rises to ~2.6V, do outputs 12V, 24V etc appear? When plugged in, are they still dead?

[mike123333]

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

the STBY voltage goes to 2.6v but there is no 12v or 24v. I did find a dead LED on the main board but I don't think this would affect anything?

[tom66]

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

Dead LED? What do you mean?

I think your problem is with the P/S. I will try and find schematics though for LG PSUs they are usually made of unobtanium.

[mike123333]

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

dead meaning when I set my meter in diode mode the light will not emit. I have tested others on the board that work fine.. I don't think it would casue any issues.

When I aquired the TV my freind mentioned that the TV shutdown in a power outage. When I got the tv there was a ground trace on the bottom of the PS that blew I rewired that and then noticed the rectifier and mofset having the issues. Since then those 2 components were replace..I just wanted to add those comments as to the background of the issues that the tv went through.

[tom66]

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

Some meters can't provide enough voltage drop to light certain high brightness green, blue or white LEDs.

I would advise you start checking all the diodes on the output side of the power supply.

[mike123333]

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

I am using a fluke 179 which I would assume to be a good meter. I checked them before but will check them again. What about electrolytic caps, i do not have an esr meter to check. I am wondering whether maybe they are posing any issues even though they physically look good. I may remove them and test one at a time with capacitance.

[selldoor]

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

Hi if you start checking caps start with the small ones on the primary side may be 50v68uf - one of them will be a start up cap. Just to check, you did test both orange fuses?

[mike123333]

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

yes I did check the orange fuses they were tied together. They checked out good.