Philips 42PFL3704D LCD no power

[lotr]

I bought this Philips tv about 1 1/2 years ago, from that time on two occasions the tv turned off and would not turn on until I unplugged and plugged the power cord back in.

The third and final time it did the same thing however after turning off the tv it would not turn back on and there is no power led or standby led either.

The remote or the power button on the tv does nothing when pressed. When I unplug and plug the power cord there is a clicking sound and nothing else.

I have read some threads here and my problem sounds similar to some threads where the problem was bad capacitors. I open the back case and looked but all the capacitors look good ( I know from reading that they still may not be up to standard ). The majority of the capacitors are Su'scon and there are a few Jamicon.

I have taken pictures and would appreciate any advice before I go ahead and try to replace the capacitors.

Thanks

[randtek]

Re: Philips 42PFL3704D LCD no power

One problem I am aware that this model can have that causes no power requires the replacement of these resistors on the power/inverter board with the following values. Resistors on the board may not be these exact values. Use these instead.

R1217 820K 1/4 W
R1218 820K 1/4 W
R1219 390K 1/4 W

[PlainBill]

Re: Philips 42PFL3704D LCD no power

I bought this Philips tv about 1 1/2 years ago, from that time on two occasions the tv turned off and would not turn on until I unplugged and plugged the power cord back in.

The third and final time it did the same thing however after turning off the tv it would not turn back on and there is no power led or standby led either.

The remote or the power button on the tv does nothing when pressed. When I unplug and plug the power cord there is a clicking sound and nothing else.

I have read some threads here and my problem sounds similar to some threads where the problem was bad capacitors. I open the back case and looked but all the capacitors look good ( I know from reading that they still may not be up to standard ). The majority of the capacitors are Su'scon and there are a few Jamicon.

I have taken pictures and would appreciate any advice before I go ahead and try to replace the capacitors.

Thanks

This is one of those Philips abominations that has parts of the power supply on the Small Signal Board. The Service Manual is on Elektrotanya. I'd check the fuses, then check the outputs of the power supplies. If it follows true to form, the standby supply is on the SSB, and provides start-up power to the main supply.

PlainBill

[lotr]

Re: Philips 42PFL3704D LCD no power

One problem I am aware that this model can have that causes no power requires the replacement of these resistors on the power/inverter board with the following values. Resistors on the board may not be these exact values. Use these instead.

R1217 820K 1/4 W
R1218 820K 1/4 W
R1219 390K 1/4 W

I checked the service manual and it says:

R1217 820K 1/4W
R1218 820K 1/4W
R1219 820K 1/4W

Should I change just R1219 to 390K?

This is one of those Philips abominations that has parts of the power supply on the Small Signal Board. The Service Manual is on Elektrotanya. I'd check the fuses, then check the outputs of the power supplies. If it follows true to form, the standby supply is on the SSB, and provides start-up power to the main supply.

PlainBill

I checked the fuse and it is giving a resistance of 0.7 ohms which I believe reading in one of the threads was an ok value.

I checked the input voltage from the power chord on the circuit board at CN1601 and there is 120V AC coming in.

I could not find where to check for the standby voltage but I did check the voltage on CN1501 which is taking power to CN601 on the signal board and the schematics say there should be 22V DC but when I check the reading is OV DC.

I believe this may be the problem any ideas on what could be causing this?

[PlainBill]

Re: Philips 42PFL3704D LCD no power

This is another variation of the dual supply approach. Yes, the missing voltage is very significant.

Patience, please. I'm working my way through this abomination. Apparently the 22V is generated on the signal board.

Yes, that is correct, and I'm out of my depth. The resistors R603, R604, R605, R606 are part of the start-up circuit for the power supply which generates the 22V (and other voltages). This controller does not have any ICs, someone brighter than I am is going to have to help if the resistors are good.

PlainBill

[randtek]

Re: Philips 42PFL3704D LCD no power

I cannot really elaborate further due to confidentiality issues. Just replace all 3. Resistors are cheap, only a few cents each.

[retiredcaps]

Re: Philips 42PFL3704D LCD no power

I cannot really elaborate further due to confidentiality issues.

Sounds like a technical service bulletin with a "we f*****d up, change the resistor value to this before the class action suits start".

Hopefully it fixes the problem for the OP and good info to have for others in the future.

[randtek]

Re: Philips 42PFL3704D LCD no power

Sounds like a technical service bulletin with a "we f*****d up, change the resistor value to this before the class action suits start".

I can neither confirm, nor deny the veracity of this statement.

[lotr]

Re: Philips 42PFL3704D LCD no power

I changed all three resistors, no luck.

Still the same problem, clicking can be heard when tv is plugged and unplugged otherwise nothing, no power led no other sounds.

Any other suggestions on what I can check to see why there is no power going from the inverter/power board to the signal board?

[retiredcaps]

Re: Philips 42PFL3704D LCD no power

I changed all three resistors, no luck.

With the values suggested by randtek?

[lotr]

Re: Philips 42PFL3704D LCD no power

Yes, I used 820K 1/4W for both R1217 and R1218 and used 390K 1/4W for R1219.

I checked the resistors with a meter before using them and the connections are good on the board.

[PlainBill]

Re: Philips 42PFL3704D LCD no power

With the schematics it should be possible to troubleshoot this power supply. Note the it involves dealing with voltages that are certainly painful, probably life-altering, and if you get very careless, possibly life-ending. Are you interested?

PlainBill

[lotr]

Re: Philips 42PFL3704D LCD no power

Yes, I am interested (as long as your not suggesting I use my hands to check voltages ).

If you can provide instructions on what to do I do not believe I will have problems.

Thanks.

[PlainBill]

Re: Philips 42PFL3704D LCD no power

OK, I'll expect you to exercise all safety precautions. It's football Sunday, so I will be otherwise occupied for most of the day. So you won't be bored, I've marked up a part of the schematic that is critical. I still don't know exactly what is going on here, but I have many points to check.

I've circled two transistors and 1 opto-isolator in yellow. What are the voltages on those points? Use pin 3 of T601 as the ground point for the two transistors and the output of the opto-isolator. Use Pin 12 of T601 for the input side of the opto-isolator. These measurements should be made with all boards connected, and power on.

I've also circled a large number of semiconductors in blue. Check those with power off and after you have given the caps time to discharge (half an hour should do it). I suggest a double test. First put your DMM on the 200 ohms scale and check across each diode. I would expect most to measure over 200 ohms, a reading of less than 100 ohms should be noted, less than 10 ohms is a 'smoking gun'. Second, with the DMM on the diode test range check the diodes in both directions. You should get a reading in only one direction.

PlainBill

[lotr]

Re: Philips 42PFL3704D LCD no power

Appreciate the help even on football Sunday.

I have not checked the voltages yet because I can not flip the board because there are cables on two different sides of the board and because of the tightness of the heatsink and transformer I can not get the test lead in without touching something. So I am going to buy some test leads with a mini grabber and then check the voltages.

I did check the diodes and there are some interesting results.

(Note: two diodes on the schematics were not installed on the board, D605 and D614)

First I put the DMM on the 200 ohms setting and checked the diodes and could only get a momentary reading flash on the screen and then nothing for all the diodes you circled except D609 which got a reading of 2 ohms.

The strange thing is that all the diodes on the hot side of the board only gave that momentary flash reading however there are diodes on the cold side and all of them give readings on the 200 ohms setting.

Next I switched to the diode check setting on the DMM, all the diodes except D609, D611 and D612 gave readings only in one direction.

The three listed above gave readings in both directions and the values were:

D609 2 ohms both directions
D611 620 898
D612 148 ohms both directions

I am guessing all three will need to be replaced.

[PlainBill]

Re: Philips 42PFL3704D LCD no power

Appreciate the help even on football Sunday.

I have not checked the voltages yet because I can not flip the board because there are cables on two different sides of the board and because of the tightness of the heatsink and transformer I can not get the test lead in without touching something. So I am going to buy some test leads with a mini grabber and then check the voltages.

I did check the diodes and there are some interesting results.

(Note: two diodes on the schematics were not installed on the board, D605 and D614)

First I put the DMM on the 200 ohms setting and checked the diodes and could only get a momentary reading flash on the screen and then nothing for all the diodes you circled except D609 which got a reading of 2 ohms.

The strange thing is that all the diodes on the hot side of the board only gave that momentary flash reading however there are diodes on the cold side and all of them give readings on the 200 ohms setting.

Next I switched to the diode check setting on the DMM, all the diodes except D609, D611 and D612 gave readings only in one direction.

The three listed above gave readings in both directions and the values were:

D609 2 ohms both directions
D611 620 898
D612 148 ohms both directions

I am guessing all three will need to be replaced.

The 'momentary flash' is normal. The DMM is charging the caps.

D609 is good, it is in parallel with R614. No value is specified for R614, but it is a current sense resistor so it would be in the .2 - 5 ohm range. D612 is a similar situation. It is in parallel with R615, a 150 ohm resistor.

D611 is interesting. There shouldn't be any leakage paths, but I don't see how that could hold the power supply off. If it's a through-hole diode, I may ask you to test it out of circuit.

Please do the same tests on Q601 and Q602. If Q602 is shorted it would kill the power supply and possibly alter the reading on D611.

PlainBill

[lotr]

Re: Philips 42PFL3704D LCD no power

I don't know much about transistors so I did some reading and hopefully I measured it correctly.

I have number the pins in the attachment to help with this explanation.

On Q601, I had the red test lead on pin 3 and moved the black test lead from pin 2 to 1, using the diode check setting on DMM and measured readings only one way. The 200 ohms setting I got the momentary reading like the others from before.

On Q602, I had the black test lead on pin 2 and moved the red test lead from pin 1 to 3, using the diode check setting measured readings only one way. The 200 ohms setting I got the momentary reading like the others from before.

[PlainBill]

Re: Philips 42PFL3704D LCD no power

I don't know much about transistors so I did some reading and hopefully I measured it correctly.

I have number the pins in the attachment to help with this explanation.

On Q601, I had the red test lead on pin 3 and moved the black test lead from pin 2 to 1, using the diode check setting on DMM and measured readings only one way. The 200 ohms setting I got the momentary reading like the others from before.

On Q602, I had the black test lead on pin 2 and moved the red test lead from pin 1 to 3, using the diode check setting measured readings only one way. The 200 ohms setting I got the momentary reading like the others from before.

Well, those check out. I'll look over the schematic again, but I'm afraid it's going to take voltage readings to narrow this down.

PlainBill

[lotr]

Re: Philips 42PFL3704D LCD no power

Attached pic to help with explanation.

Q601 with ground on pin 3 of T601.

Pin 1 (on 200M setting on DMM), 2.8
Pin 2 (on 200V setting on DMM), 169
Pin 3, 0

Q602 with ground on pin 3 of T601

Pin 1, 0
Pin 2 (on 200M setting on DMM), 8.6
Pin 3, 0

IC601 with ground on pin 3 of T601

Pin 3, 0
Pin 4 (on 200M setting on DMM), 13.6

IC601 with ground on pin 12 of T601 (I am assuming that the pin layout is like IC chips for T601
8 7 6 5 4 3 2 1
9 10 11 12 13 14 15 16
or is it like the schematics where it is the last pin)

Pin 1, 0
Pin 2, 0

[PlainBill]

Re: Philips 42PFL3704D LCD no power

Attached pic to help with explanation.

Q601 with ground on pin 3 of T601.

Pin 1 (on 200M setting on DMM), 2.8
Pin 2 (on 200V setting on DMM), 169
Pin 3, 0

Q602 with ground on pin 3 of T601

Pin 1, 0
Pin 2 (on 200M setting on DMM), 8.6
Pin 3, 0

IC601 with ground on pin 3 of T601

Pin 3, 0
Pin 4 (on 200M setting on DMM), 13.6

IC601 with ground on pin 12 of T601 (I am assuming that the pin layout is like IC chips for T601
8 7 6 5 4 3 2 1
9 10 11 12 13 14 15 16
or is it like the schematics where it is the last pin)

Pin 1, 0
Pin 2, 0

OK, Q601 is being held off. The drain voltage is low

Q602 readings are screwy. The collector is at 8 mv, while the base and emitter are at 0 volts. The collector voltage makes sense, it's tied to the gate of Q601.

On the attached picture, the components circled in blue pull the gate of Q601 / collector of Q602 high. Those circled in green pull them low.

Remove C603 from the board and measure the resistance across it.

If you can do this safely, I'd like to know the voltage at the junctions between R603 and R604, R604 and 605, R605 and R606.

PlainBill