42pfl7422d/37 help

[afrelientk]

I have a Philips 42 inch 42PFL7422D/37 that I got from a friend. He said one day it just stopped working. There is no sound or picture. The little blue light does come on once I connect it to power but thats it. Turned all the lights off and there was no picture. I did connect a USB to it to try a firmware update and it definitely did read my USB because the USB lights flickered but that didnt help. I have checked all of the capacitors and have found no damage. The 820UF 250V capacitors were slightly bulged but the X imprinted on it was not. I have checked all the chips on it to see if any of them were burnt out but I found no damage. I have pulled this LCD apart and have not found any visible damage. Can anyone offer any advise for this? Thanks!

-Kyle

[PlainBill]

Re: 42pfl7422d/37 help

Check the voltage out of the power supply. Does the PS_ON (or equivalent) signal change when the power button is pressed? These inverters have a long history of problems.

PlainBill

[afrelientk]

Re: 42pfl7422d/37 help

I checked the voltage on all of the boards and they are all recieving power. I am attaching pictures of the circuit board after I connect it to power. Should all of the lights come on (of the 5 light set) Only three out of the five are lit. Any other suggestions? Thanks for the help!

[afrelientk]

Re: 42pfl7422d/37 help

Also when I hit the power button on the TV the light in the upper right left hand corner turns off then all of the lights turn off.

[afrelientk]

Re: 42pfl7422d/37 help

Any help with this would be awesome

[tom66]

Re: 42pfl7422d/37 help

There looks to be a relay on the PSU board. Do you hear any clicks when the TV power button is pressed?

[afrelientk]

Re: 42pfl7422d/37 help

There looks to be a relay on the PSU board. Do you hear any clicks when the TV power button is pressed?

When I plug the TV in the lights come on then they click off about 20 seconds later. When I press the power button they come back on. When I press it again, it does click and all the lights go off again. Is that normal?

[afrelientk]

Re: 42pfl7422d/37 help

Check the voltage out of the power supply. Does the PS_ON (or equivalent) signal change when the power button is pressed? These inverters have a long history of problems.

PlainBill

I checked the voltage going into the capacitors on each invertor board. They both were reading 051 on each capacitor. Is this a normal reading?

[tom66]

Re: 42pfl7422d/37 help

I checked the voltage going into the capacitors on each invertor board. They both were reading 051 on each capacitor. Is this a normal reading?

What range did you have your meter on?

Do you hear any sound if you plug in a device to one of the inputs, or use the antenna?

[afrelientk]

Re: 42pfl7422d/37 help

What range did you have your meter on?

Do you hear any sound if you plug in a device to one of the inputs, or use the antenna?

500V was the range. When I connect my laptop to the computer via HDMI my laptop detects the television but I get no sound. When i press the source button on my remote I can tell the TV is cycling through the sources and on one source(not sure which one because no picture) there is alot of muffling coming out of the speakers. It is kinda strange.

[afrelientk]

Re: 42pfl7422d/37 help

500V was the range. When I connect my laptop to the computer via HDMI my laptop detects the television but I get no sound. When i press the source button on my remote I can tell the TV is cycling through the sources and on one source(not sure which one because no picture) there is alot of muffling coming out of the speakers. It is kinda strange.

the muffling happens whether or not anything is connected to the television.

[tom66]

Re: 42pfl7422d/37 help

The muffling is a potential symptom, but it seems more likely the case of the TV has some effect on the sound, or the speakers or integrated amplifier is faulty. Either way, it's a problem to fix later - the main problem is the lack of picture.

Try the 50V or a lower range. Decrease the range until the reading reads "1 ." or "OL", then use the range above. 51V is very high for an inverter, although I've heard of 48V inverters.

Can you post a closer picture of the inverter, and around the connector and capacitors?

[afrelientk]

Re: 42pfl7422d/37 help

The muffling is a potential symptom, but it seems more likely the case of the TV has some effect on the sound, or the speakers or integrated amplifier is faulty. Either way, it's a problem to fix later - the main problem is the lack of picture.

Try the 50V or a lower range. Decrease the range until the reading reads "1 ." or "OL", then use the range above. 51V is very high for an inverter, although I've heard of 48V inverters.

Can you post a closer picture of the inverter, and around the connector and capacitors?

I had the meter on V~ 200 this time(in the picture). I am kinda a nuub to ohmmeters.

[tom66]

Re: 42pfl7422d/37 help

I had the meter on V~ 200 this time(in the picture). I am kinda a nuub to ohmmeters.

You want to set it to "V=", not "V~". V~ is for AC (like out of the mains plug); V= is for DC, like out of a battery or going to an inverter.

I was hoping to see a voltage rating on those caps, unfortunately there is not (it's probably on the bottom.) You might have to unplug the inverter board and take pictures of the underneath. But before you do that, measure the voltage using DC instead of AC. To avoid any doubt, set the meter to the range I've highlighted.

[tom66]

Re: 42pfl7422d/37 help

As I am going to bed soon (11.30pm here), here are a few other checks you can perform.

Both tests should be performed with the TV off. It's very important that it's off or you could damage your meter.

For the red circled fuse: set your meter to the diode/beeper range (highlighted in red on the meter image). Touch the two probes of your meter together. If you hear a beep, that's good. Then touch the leads on the fuse. Hear a beep? If so the fuse is good.

For the blue circled pins. Test each separately. Set your meter to the "20000" ohms range, highlighted in blue. Test the resistance between the upper and lower pins. Record the result. Then, for the lower transformer, do the same. There should be very little difference between each measurement, if there is a difference, then one of the transformers is bad (usually the one with the highest resistance is bad); the good news is this is a cheap fix.

[electrodog]

Re: 42pfl7422d/37 help

I'm a newbie, so I don't know if I'm posting this in the correct place, but here goes. I have a 42pfl7422d/37 no picture no sound. When I turn it on, the relay clicks, the blue power LED comes on but no picture or sound. After about 10 seconds the relay clicks again. Inside on the main board there are I think 2 blinking green LED's, one solid green, and looks like 2 that are not lit. When the relay clicks for the second time, all of the LED's go out. Then after about 20 seconds, the cycle starts over where the TV is trying to come back up, and just repeats, off, on, off, on. It is not the power supply, I replaced it, same problem. I normally don't like to shotgun troubleshoot, but I've been looking around on the internet for many hours and have not found a solution. The power supply only cost me $64. I just ordered the main board (SSB) for $59. For me, time is money, but if anyone can help it would be much appreciated. Thanks from a newbie.

[budm]

Re: 42pfl7422d/37 help

@electrodog, did you look real close at the two inverter boards to see if they have any damaged IC, fuses and MOSFET's on the Inverter boards since these boards are know to have blown IC and MOSFET's.
They will require modification if they are not done also.

[electrodog]

Re: 42pfl7422d/37 help

No, I have not gone that far removing the covers on the inverter boards, but can you tell me, will that cause the symptoms as I have described (no picture and no sound)? From what I have read so far, a bad inverter usually manisfests symptoms of no picture, but the audio is ok. Correct me if I am wrong, thanks.

[budm]

Re: 42pfl7422d/37 help

If the inverter board shorted out, it will cause the 24V (for backlights) and 12v (for sound) power supply to shutdown, the 12V and 24V power supplies are generated by the same circuits. Best thing to do when you try to fix anything is to do visual inspection first. There is no 100% sure what have gone out since more than one circuit can also cause the same symptom.

[electrodog]

Re: 42pfl7422d/37 help

Yes, thankyou, I have done a visual inspection of the PS and main board looking for bad caps, burned components etc. As I mentioned, I haven't inspected the inverters, maybe while I'm waiting on my new main board, I'll check the inverter boards. Also, you provided me with an inverter modification II document. Should I assume this is something that needs to be done even if it is not the cause of my failure? What does the inverter mod fix? What is the failure mode that required this fix?