PHILLIPS 42PFL3704D F7 no 5v standby after replacing fuse

[triplefour]

so i got this tv from a client today. i sold them the vizio 37 inch from this thread:https://www.badcaps.net/forum/showth...t=38097&page=3
the reason they were buying a new tv turned out to be because their old one had just stopped working.
so i offered to try to fix it for them...
when i plugged it in, nothing happened. no standby led or anything.
so i took the back off of it and what did i find?
the tail of a gecko sticking out from under the PSU board!
so now i know that most likely the gekko crawled in there when the tv was off and got electrocuted when the tv was turned on. and on his way, he probably took some stuff out.

i checked the fuse and saw that it was open.
luckily i had the same fuse in another tv so i swapped fuses and plugged it in.
still no standby light
the fuse did not blow and i see 120 AC volts there
i cant see any other voltages except 120 volts DC on the power connector going between the 2 boards.
but im not even sure where the 5v standby would be as the boards are strange to me and unlabeled...
i might just save myself the time and tell her to buy a new PSU, but i figured its worth trying if maybe i can find the fault easily...or ill order the new board but ill have a few days to try and fix it before it comes in. if i am able to fix the board then i can give/sell it to her as a spare, or sell it on ebay.


anyone seen one of these before?

[triplefour]

Re: PHILLIPS 42PFL3704D F7 no 5v standby after replacing fuse

some more pics of the connectors

[triplefour]

Re: PHILLIPS 42PFL3704D F7 no 5v standby after replacing fuse

http://www.ebay.com/itm/BA94H0F0103-...item20ed1d2ad9

this board really looks the same but the model is slightly off..but it came from the same model tv...probly works yea?

[cliff_hootarski]

Re: PHILLIPS 42PFL3704D F7 no 5v standby after replacing fuse

Saw a version of this power supply the other day. Resoldered most components on the primary side of the power supply and fixed it.

[triplefour]

Re: PHILLIPS 42PFL3704D F7 no 5v standby after replacing fuse

u mean u took all the components out and just soldered em back in, or u just reflowed all the joints?

[Agent24]

Re: PHILLIPS 42PFL3704D F7 no 5v standby after replacing fuse

u mean u took all the components out and just soldered em back in, or u just reflowed all the joints?

Both would have the same result, reflowing the joints is much easier though

[Caleb]

Re: PHILLIPS 42PFL3704D F7 no 5v standby after replacing fuse

have you checked the ceramic resistor for continuity? checked the fets for shorts?

[budm]

Re: PHILLIPS 42PFL3704D F7 no 5v standby after replacing fuse

This is another one of those bad design two-transistor switching power supply used in EMERSON, FUNAI, SYLVANIA, PHILIPS. Check all the rectifier diodes in the secondary side also.

[Fluidguy]

Re: PHILLIPS 42PFL3704D F7 no 5v standby after replacing fuse

This is interesting

[triplefour]

Re: PHILLIPS 42PFL3704D F7 no 5v standby after replacing fuse

is it?

[budm]

Re: PHILLIPS 42PFL3704D F7 no 5v standby after replacing fuse

So can we see the bottom side of the board to see if there is any sign of damage? For that big fuse to blow, there must big current flowing though something to make it blows.
Do you also hear the AC Power relay click on?
Check to see if you do have 5VSTBY.
Pictures provided by Shopjimmy.
The sub-power supply is on the power supply-main board combo which uses two-transistor switching circuits.

[budm]

Re: PHILLIPS 42PFL3704D F7 no 5v standby after replacing fuse

I found the Service manual

http://elektrotanya.com/?q=showresul...oria=&kat2=all

[triplefour]

Re: PHILLIPS 42PFL3704D F7 no 5v standby after replacing fuse

ok i finally got to this one. i do not hear any ac relay click. there is no voltage on that capacitor c1104 and there is no voltage on either of the big capacitors on the board. i looked really hard and i cant see anything damaged on the top or the bottom of the board.
can you tell me which are the rectifier diodes in the secondary circuit?

edit: r1602 right next to the fuse has infinite resistance on the highest ohm setting...could this be the only problem? something tells me not

edit: i have a short between drain and source on the Q1601 mosfet and almost a short on the Q1602 mosfet with 1ohm between drain and source (in the PFC section)

pin 1,2,3 from the left = gate, drain, source right?

all the diodes in the 5v standby section seem fine

no shorts on q1203 mosfet in the 5v standby section

[Caleb]

Re: PHILLIPS 42PFL3704D F7 no 5v standby after replacing fuse

those resistors right next to the fuse should be very high ohms. if you've got no voltage to the main cap for the 5v then either the diodes are open or the choke is

[triplefour]

Re: PHILLIPS 42PFL3704D F7 no 5v standby after replacing fuse

i dont know what you mean by choke...the diodes arent open. the resistor is tho

[budm]

Re: PHILLIPS 42PFL3704D F7 no 5v standby after replacing fuse

I would remove those two power MOSFETs from the PFC section and test them, if the relay comes on ,it will blow the main fuse again.
So you do not have 160Vdc Voltage at C1201?
Did you download the service manual?

[Caleb]

Re: PHILLIPS 42PFL3704D F7 no 5v standby after replacing fuse

i dont know what you mean by choke...the diodes arent open. the resistor is tho

I labeled the picture to make it plain, the voltage only travels through the fuse, choke, and diodes before reaching the cap.
A choke can also be called a torrid, coil, or inductor its the round thing with lots of wire wrapped around it.

[triplefour]

Re: PHILLIPS 42PFL3704D F7 no 5v standby after replacing fuse

sorry i didnt see that u labeled those areas. thanks! learned a new word today...choke!

[budm]

Re: PHILLIPS 42PFL3704D F7 no 5v standby after replacing fuse

http://www.wisegeek.org/what-is-a-choke-coil.htm

http://en.wikipedia.org/wiki/Choke_(electronics)

http://www.butlerwinding.com/store.asp?pid=28349

[triplefour]

Re: PHILLIPS 42PFL3704D F7 no 5v standby after replacing fuse

well the board came in, and i replaced it and everything is fine now...they havent picked it up yet but i imagine they will let me keep the dead board...idk how ill finish fixing and testing it though, since it seems the psu was split across the 2 boards...