Philips 42PFL7422D/37 Backlight Issue

[jthi]

Hey Forum,

This place has been a huge help in reading through, but I'm still having some issues tracing down my issue. I'm a home DIYer, so I don't have access to some of the specific tools I read others using, pretty much just the standard multimeter.

With that as a preface, on to my issue. I received the tv from my brother with the symptoms of no video but it does get sound. I can see with a flashlight, that the picture is there, but there is no backlight. The specifics on what actually happens is this: when I plug in the TV, I hear a relay click, and then I power the TV on. I get a basic source picture for 2 seconds, then the backlight turns off.

I thought this was the classic 2 seconds to black issue, but I got lost in troubleshooting down to the component levels. I ended up ordering a new Master and Slave Inverter, and wouldn't you know it, it didn't fix my issue, so I promptly order a new PSB. No change. I've already beaten myself up repeatedly for dropping dumb money on this twice, and now I'm ready to speak up and let the forum slam me - and then hopefully offer some suggestions.

Btw, non of the boards look to have any visual issues like bad caps or fried chips (hopefully swapping to new boards confirms this). The only one I haven't pulled out is the T-Con board, but from what I read, I didn't think it would be an issue.

I have noticed that I could make one different thing happen. When I replace just the new Master Inverter (and leave all old parts in), the TV does all the same stuff but I get no initial flash of backlight. Not sure if that could help point to something, but figured I'd mention it. I appreciate all the info here, and any help, even if it's pointing to something I may have missed is greatly appreciated.

[jthi]

Re: Philips 42PFL7422D/37 Backlight Issue

Updating with photos - hopefully they help

[tom66]

Re: Philips 42PFL7422D/37 Backlight Issue

You may well have a problem with one of the CCFLs inside the TV.

When you turn it on very carefully look for any part of the screen that looks a bit dimmer than the rest.

If you can't see any part, then you may have to disassemble the LCD panel to get to them (that's very difficult.) And replacements may not be readily available...

That being said I have seen no LCD TVs yet with a failed CCFL (save for a 22"); the bigger ones seem to last much longer. Not sure if that is just confirmation bias.

[jthi]

Re: Philips 42PFL7422D/37 Backlight Issue

Thanks for the reply Tom. I can quickly hit the menu button during that initial 2 secs, and everything across the screen looks good.

I'm starting to wonder if my replacement Master Inverter might be bad as well, but that's just me taking a guess.

[tom66]

Re: Philips 42PFL7422D/37 Backlight Issue

Thanks for the reply Tom. I can quickly hit the menu button during that initial 2 secs, and everything across the screen looks good.

I'm starting to wonder if my replacement Master Inverter might be bad as well, but that's just me taking a guess.

It could be. Do you have a digital multimeter? Take a picture of your Master board and we can highlight some tests to do.

[bbjunkie]

Re: Philips 42PFL7422D/37 Backlight Issue

Thanks for the reply Tom. I can quickly hit the menu button during that initial 2 secs, and everything across the screen looks good.

I have a 22" Samsung with a bad ccfl - when it powers up initially I can do the same, to look at the menu it's almost impossible to tell there is a tube out.
So much so I am trying to fool the inverter into not cutting out and using it as is.

Moral of the story, you could still have a tube out.

[jthi]

Re: Philips 42PFL7422D/37 Backlight Issue

Tom - highlighted tests would be a great help for me! Do I need to upload a different picture than the 4th one up above? I do have a multimeter, just a little direction on where to put the probes would be great. Thank you!

bbjunkie - how are you able to fool the inverter into not cutting out?

[bbjunkie]

Re: Philips 42PFL7422D/37 Backlight Issue

jthi - trying to dummy load it with same resistance/capacitance as a working tube. Not had much luck yet, but its not high on my list right now.

[retiredcaps]

Re: Philips 42PFL7422D/37 Backlight Issue

Upload a picture of the multimeter too.

[jthi]

Re: Philips 42PFL7422D/37 Backlight Issue

The basic Crafstman DMM

[tom66]

Re: Philips 42PFL7422D/37 Backlight Issue

Tom - highlighted tests would be a great help for me! Do I need to upload a different picture than the 4th one up above? I do have a multimeter, just a little direction on where to put the probes would be great. Thank you!

Sorry, didn't notice your pictures.

Set your meter to ohms, 20k.

Turn the TV off.

Test the resistance between red and red, and blue and blue. (The metal pins on the transformers.) You should measure the same or nearly the same.

Test the resistance between green and green, you should measure <2 ohms. Don't confuse "1" on the left hand side with 1.0 ohms. This component is a fuse.

[retiredcaps]

Re: Philips 42PFL7422D/37 Backlight Issue

Test the resistance between green and green, you should measure <2 ohms. Don't confuse "1" on the left hand side with 1.0 ohms. This component is a fuse.

For the green or fuse, set the multimeter to 200 (two hundred) for more accurate reading and resolution.

[jthi]

Re: Philips 42PFL7422D/37 Backlight Issue

Thank you Tom for the quick help! I measured Red to Red as Open (1 on the left), Blue to Blue as closed (0.3 Ohms on 200 setting), and Green to Green measured as closed (0.3 Ohms on 200 setting) as well.

I swapped to my old board to check it as well and received the exact same readings on all 3. If I lable your left most red mark as 1, I can measure Red 1 to Blue 1 as open and Red 2 to Blue 1 as closed. Not sure if that's anything valid for the two transforms, but thought I'd throw it in there.

[retiredcaps]

Re: Philips 42PFL7422D/37 Backlight Issue

Not sure if that's anything valid for the two transforms, but thought I'd throw it in there.

What tom66 is trying to identify are the secondary inverter transformer pins. The readings you got suggest they may not be the right ones.

Are there any markings on part numbers on the actual transfomer?

edit: Your fuse is good.

[jthi]

Re: Philips 42PFL7422D/37 Backlight Issue

Retiredcaps - Is it possible I wasn't doing something right when reading the resistance? I tried putting the probes everywhere I could (on the solder, on each pins, etc) and I couldn't get anything besides open on them.

Here's what I see on the sides of the transformers:
Old:
T51 0165 211 e1
0726 70 8S

New:
T51.0165.211 e2
0734 70 9S

[retiredcaps]

Re: Philips 42PFL7422D/37 Backlight Issue

New:
T51.0165.211 e2

Posts #21 to #23 are applicable to you (so I don't have to repeat myself).

https://www.badcaps.net/forum/showth...t=17639&page=2

[jthi]

Re: Philips 42PFL7422D/37 Backlight Issue

Thank you sir. Let me start working through that, and I will get some better pictures up.

[jthi]

Re: Philips 42PFL7422D/37 Backlight Issue

Here are some better pictures of the original boards I have placed in the TV.

[retiredcaps]

Re: Philips 42PFL7422D/37 Backlight Issue

Okay, those are excellent pictures and thanks for getting the multimeter in the picture, but I think I'm still not making myself clear to you or the person in the other thread.

Thankfully, in one of your pictures, I see the word LOGAH on the inverter board. Again, this may not be your exact inverter, but if you take a look at this picture (it too is a LOGAH)

http://www.lcdparts.net/TransformerD...ProductID=3619

you will see that the secondary pins are S1 and S2. They are on opposite sides on the transformer.

For your board, I believe S1 is the one facing the ccfl connectors. P1, P2, and S2 are the other side.

So measure the resistance between S1 and S2 with your multimeter set on 20K. Post your measurements for all inverter transformers.

[jthi]

Re: Philips 42PFL7422D/37 Backlight Issue

I checked out the LCDparts website that retiredcaps previous post directed me to, and the closed match I could find suggested that S1 and S2 are like my attachment indicates. When I test those points, here are the resistances I get:

Old Master Inverter:
T1 (edge): S1 to S2 = Open (on 20k Ohms setting)
T2 (inside): S1 to S2 = 22.5 Ohms (on 200 Ohm setting)

New Master Inverter:
T1 (edge): S1 to S2 = Open (on 20k Ohms setting)
T2 (inside): S1 to S2 = 23.2 Ohms (on 200 Ohm setting)

Old Slave Inverter:
T1 (edge): S1 to S2 = Open (on 20k Ohms setting)
T2 (inside): S1 to S2 = 23.2 Ohms (on 200 Ohm setting)

New Slave Inverter:
T1 (edge): S1 to S2 = Open (on 20k Ohms setting)
T2 (inside): S1 to S2 = 23.4 Ohms (on 200 Ohm setting)

I also did the test where I removed the power cable to the ccfls, first from the master inverter, then testing with the slave inverter cable removed. Both tests had the tv no longer giving me the 2 secs of screen before going black. It was just black the entire time.

Is there anything else I can do before cracking it open further to check out the ccfls?