Philips 42PFL3704D LCD no power

[lotr]

Re: Philips 42PFL3704D LCD no power

I removed C603 from the board but did not get any resistance reading with the DMM.

I am not sure what you mean by the voltage at the junctions between two resistors. I took readings with the test leads before and after each of the resistors (R603, R604, R605, R606). I took these readings with C603 back on the board.

R603 140V
R604 0
R605 0
R606 0

When I went to check the voltage on R603 there was a noise for about 1 sec and then there was a click sound and another click 1 sec later and then no other noise. Also the power button on the tv and remote when pressed would also make the click sound and another click sound 1 sec later which was not happening before. The tv power led does not go on just the clicking sound. However if I unplug the tv and then plug it back in the power button on the tv and remote do nothing like before when pressed.

[PlainBill]

Re: Philips 42PFL3704D LCD no power

I removed C603 from the board but did not get any resistance reading with the DMM.

I am not sure what you mean by the voltage at the junctions between two resistors. I took readings with the test leads before and after each of the resistors (R603, R604, R605, R606). I took these readings with C603 back on the board.

R603 140V
R604 0
R605 0
R606 0

When I went to check the voltage on R603 there was a noise for about 1 sec and then there was a click sound and another click 1 sec later and then no other noise. Also the power button on the tv and remote when pressed would also make the click sound and another click sound 1 sec later which was not happening before. The tv power led does not go on just the clicking sound. However if I unplug the tv and then plug it back in the power button on the tv and remote do nothing like before when pressed.

Bingo!!! You have found the area of the problem. I'd check the solder joints in that area.

If you look only at the resistors R603, R604, R605, R606, and R609 you will see you had four 490K resistors in series with a 100K resistor. Previously you had measured 169 volts at the drain of Q601. The reisitanc of the transfomer winding is negligible, the voltage at the top of R603 can be assumed to be 169 volts. The 5 resistors in series have a resistance of 2060K ohms. I would have expected a drop of 40 volts across each of the first four resistors and about 9 volts across R609.

When I say 'voltage at the junctions between R603 and R604, R604 and 605, R605 and R606', I mean place the black lead on a live ground point (the lower end of R609 is a good point) and measure the voltage at the point where R603 connects to R604, R604 to R605, etc. I would have expected that you would have seen 129, 89, 49, and 9 volts.

PlainBill

[lotr]

Re: Philips 42PFL3704D LCD no power

I would like to say thanks for being patient as I only know the basics and am trying to learn as we go.

I checked the solder joints and they all look okay and there is no movement for any of the resistors.

There is no R609 installed on the board so I used R611 as the live ground point (if I read the schematics correctly) where I placed the black test lead.

Now when I usually check to see where one component is connecting to another component I check the trace lines, however there is no trace lines on the hot section on the top or bottom of the board.

I checked the voltages for all four of the resistors by placing the red test lead before and after each resistor (take a look at pic). I got a reading of 169V on the before pin of R603 and 0 for all other readings.

[PlainBill]

Re: Philips 42PFL3704D LCD no power

I would like to say thanks for being patient as I only know the basics and am trying to learn as we go.

I checked the solder joints and they all look okay and there is no movement for any of the resistors.

There is no R609 installed on the board so I used R611 as the live ground point (if I read the schematics correctly) where I placed the black test lead.

Now when I usually check to see where one component is connecting to another component I check the trace lines, however there is no trace lines on the hot section on the top or bottom of the board.

I checked the voltages for all four of the resistors by placing the red test lead before and after each resistor (take a look at pic). I got a reading of 169V on the before pin of R603 and 0 for all other readings.

You are homing in on it. There are two approaches. With power off, measure the resistance of each resistor. In a good circuit all four would read the same - somewhat below the nominal resistance I would think. If all four read 490K, measure the resistance from the after pin of R603 to the before pin of R604.

PlainBill

[lotr]

Re: Philips 42PFL3704D LCD no power

I checked the resistance of all 4 resistors.

R603 could not get a reading
R604 474K
R605 472K
R606 470K

I also checked the resistance of the after pin to the before pin of each resistor and got a reading of 0 which usually means continuity so they must be all connected.

Is the problem R603 or do I have to measure it out of circuit?

[retiredcaps]

Re: Philips 42PFL3704D LCD no power

Is the problem R603 or do I have to measure it out of circuit?

Personally, I would take it out of circuit to verify.

[lotr]

Re: Philips 42PFL3704D LCD no power

Ok, I took out the resistor and still no reading so definitely will need replacing.

Schematics call for 470K 1/4W, should this be okay or should I use another value.

[PlainBill]

Re: Philips 42PFL3704D LCD no power

Ok, I took out the resistor and still no reading so definitely will need replacing.

Schematics call for 470K 1/4W, should this be okay or should I use another value.

Use the same value.

PlainBill

[lotr]

Re: Philips 42PFL3704D LCD no power

So I replaced the resistor, checked it before and after installing, plugged in the power cord and the power led comes on and then a few seconds later the Philips logo showed up on the screen and the tv WORKS!!!!

Thanks PlainBill for all the help and hopefully this helps out other people with same problem.

If you are going to be in Toronto area let me know and I'll buy you a beer.

[Hex]

Re: Philips 42PFL3704D LCD no power

i hope this all helps me as well, ive read through the conversation and i will be attempting to test the resistors. however i believe my problem is slightly different. the tv power light comes on i hear a click and then a zap sound from the boards finally to say the tv has no picture the backlight does not even show.

soon ill open a new thread hoping to find answers.

[Hex]

Re: Philips 42PFL3704D LCD no power

i hope this all helps me as well, ive read through the conversation and i will be attempting to test the resistors. however i believe my problem is slightly different. the tv power light comes on i hear a click and then a zap sound from the boards finally to say the tv has no picture the backlight does not even show.

Soon ill open a new thread hoping to find answers.

Just a note because I'm unsure about the compatibility of the old and new board with the tv.

"the power supply is the same in the pictures, although the tv does NOT have the secondary slave inverter cable (I assume that's its name) running to the powersupply.

But DOES have the connector for the extra cable shown on the board P/N BA91H5F0103 1_A same as the old board i replaced it with just lacking the connector

Mostly i believe my problem is in the respected area of the second board on the LCD as i know the power supply is good but may not be compatible.

i do know i have power!. -just no visual-

[Phydoux]

Re: Philips 42PFL3704D LCD no power

I have one of these in my spare bedroom. Comes on for a couple minutes then the TV restarts. I had a problem with it about 8 months ago where it wouldn't come on at all. Bought a power supply board for it and it worked fine for a few months and then it started doing what it's doing now. I bought the Jack Power board which has all of the peripheral jacks on it and that didn't seem to fix the issue. I'm thinking it's the main power board again.