Philips 42PFL7422D backlight troubles

[a.dunne]

hey there!i was sent here by a friend who told me i could get some good help from this forum.ive been searching the threads for the answers to my problems and although you guys seem very knowledgable my questions are still unanswered.a couple months back i was given a 42" phillips model #42PFL7422D.chassis #Q523.1U LA i took it home and pluged it in.it powers up and the blue light is on in the front.the backlight never comes on and i can see images with a flashlight.i removed the back panel and inspected the caps,boards and connections.i came across a dark area on the main power board that looks like it got hot.i removed it to inspect for any other damage but found nothing so i reinstalled for further testing.as i stand behind the t.v and power it on i have 5 green lights on the video board and a blue light on the master inverter come on.after 3 seconds or so the blue light on the master inverter fades out..before we get too far i want to prepare you for possible dumb questions haha i do autobody for a living..im not the "go to" guy for electronics thats for sure..ive always enjoyed electronics i just never wondered how the worked..until now..i guess you gotta start somewhere right??so my first question is this...lets say the power board is good.if the slave inverter is bad would that make the master inverter fire up and die like it does?or could it still be a problem with the master inverter?does this sound like a problem the power board could be causing?im assuming the next step is to start testing so im uploading the pics ive taken so maybe you can get a better idea from that.ive never tested anything like this but with some quality guidence im sure i can have it under control haha.sorry if there not good pics.im not working with a very good camera so please let me know if you need better pics..ive also posted a pic of the multimeter i could get ahold of just to confirm that it is a good one to use..any tips or advice will be greatly appreciated!

[a.dunne]

Re: Philips 42PFL7422D backlight troubles

pics

[drpj23]

Re: Philips 42PFL7422D backlight troubles

Pictures do need to be clearer.

The master and slave do need to work together but is not common for it to take out each other (in my experience at least) (though possible I suppose)

First, we need to check if the inverters are getting 24v from the power supply and that the main is telling the inverters to cut on (i.e 3~5 v on BL-ON)

Legends are on the board (might not be right near the connector but are on the board)

Put the multimeter on DC (line over a dotted line) voltage.
Then put the black probe on the chassis (metal surface or screws holding the boards down will work) and the red on the corresponding pin you are checking.

These inverter also look like the ones that need that mod kit due to a design flaw

[tibimakai]

Re: Philips 42PFL7422D backlight troubles

I'm working on the same TV, but mine doesn't even powers up, no click, no LED.
I have different inverter boards. Yours are the famous one, that they go bad.
Usually that big IC BD89xx and the four FET transistors are the issue with them.
On Ebay they sell kits for these inverter boards if do you need them.
Measure the FET transistors across the pins and they have to show 8.5Kohm, if they don't, then it means that it needs replacing.
If do you find any one shorted, I would replace the IC with the four FET transistors and the two big capacitors.
Budm recommends to do an update on these boards, if do you research on this subject you will find the updated document. They suppose to last longer with that update.
Last time I had this issue, I have found some updated boards on Ebay, and they were brand new and very cheap($38 both), now they may be a bit more expensive.

[Dgtech]

Re: Philips 42PFL7422D backlight troubles

This is a very common failure as seen here in my post from two years ago. (#29):

https://www.badcaps.net/forum/showthr...974#post129974


I have found with this TV that:

1. If the set turns on and you get no backlight at all and you can see image with flashlight, then it will be the slave at fault.

2. If the set does not turn on, then look at the master.

If you do a search for that chip number, you will find a lot of helpful threads here on , how to troubleshoot it, where to get it, and how to replace it. That of course, includes it's surrounding parts as well (the four FET's).

[budm]

Re: Philips 42PFL7422D backlight troubles

mod info.

[a.dunne]

Re: Philips 42PFL7422D backlight troubles

thanks everyone for the replys and sorry for the late response..free time dont come around too often..

drpj23-both master and slave inverters are getting 24v

tibimakai-i measured the fet transistors and was unable to come up with a 8.5kohm reading on the master or the slave.is there any specific way i should test the fet transistors?i would like to rule out a human error possibility.

as stated before i havent had much free time to do research so heres rookie question #2..if i were to rebuild the inverters would i want to purchase the rebuild kit and the mod kit?(want to be sure the mod kit isnt just updated components of the rebuild kit)thanks for hanging in here guys i appreciate the help!!

[drpj23]

Re: Philips 42PFL7422D backlight troubles

What about the other pins on the connector?

Just put one probe on one pin and one on the other pin of the transistor and measure in the ohms Ω setting.

The rebuild kit replaces the capacitors, 4 FETs, and that IC. The mod adds some additional components and modifies the circuit a little bit so all this will not happen again lol. Or you can buy them already done for under $40 as tibimakai said.

[a.dunne]

Re: Philips 42PFL7422D backlight troubles

ok...the master checked out fine.

slave-
sq8-0.6ohm
sq9-8.4ohm
sq10-10.4ohm
sq11-10.1ohm
im hoping to find a slave that already has the mod..sounds like 40$ well spent to me lol

[tibimakai]

Re: Philips 42PFL7422D backlight troubles

With the power off, use the OHM meter and measure the two pins of each FET.
Last time I have check, both boards were almost $60, they are totally different boards, much more modern looking PCBs.
Just punch in those part numbers on Ebay and see how much they are.
The kits don't come with capacitors. Just get them from Digikey, select first class shipping, it's the cheapest. I'm not updating the boards that I'm repairing. If it breaks it's not mine design, LG or Philips are to be blamed.
Here they are:
http://www.ebay.com/itm/100-New-Inve...item35c0042d60
Shield won't fit with these boards, but it's no problem.
By the way, the IC it's not that easy to replace, just a heads up.

[a.dunne]

Re: Philips 42PFL7422D backlight troubles

yea that ic doesnt look like any fun to replace..im going to order the 2 inverters and call it good for now..i def cant complain about a $60 42" tv lol

[Losdog]

Re: Philips 42PFL7422D backlight troubles

Also not an expert, but had a similar issue, do a search for :
"Philipis 47pfl7422D/37 blinking 6 then 3".

may or may not help.

[a.dunne]

Re: Philips 42PFL7422D backlight troubles

Had some time to pull the slave to take a better look today and I came across a nice crack on the top of the ic.with little effort I had a nice chunk fall off and underneath was a burn mark.I believe ive found my culprit.I'm debating on buying new inverters or buying a rebuild and mod kit.if I were to rebuild the slave with the mod would that have any affect on the master since that won't have the mod kit?(yet..)

[Mr Bill]

Re: Philips 42PFL7422D backlight troubles

if I were to rebuild the slave with the mod would that have any affect on the master since that won't have the mod kit?(yet..)

I don't think it'll matter. The master failing in the future might be the only issue.

[budm]

Re: Philips 42PFL7422D backlight troubles

I think you will be better off buying a new set of boards like tibimakai did.
It probably has blown IC and MOSFET's plus you will need to replace the two caps plus the added caps, resistors, protection diodes to update them.
http://s807.photobucket.com/albums/y...t=DSC00215.jpg

[Dgtech]

Re: Philips 42PFL7422D backlight troubles

a.dunne - If you send me the board, I could do the repair for you at no charge. Just pay shipping. I have left over chips and I dont think I'm going to run into too many more of these boards. I've done a good bit of these in the past but I'm gonna be done with TV's pretty soon. Just let me know.

[electrodog]

Re: Philips 42PFL7422D backlight troubles

Hi budm. I want to install the inverter board mod, but looking at the LG inverter mod II v1.2 pdf, It doesn't seem clear which way to install the zener diodes. Are they showing that there is a polarity mark on the board at the pads to install the zeners? I don't want to do it wrong and install them backwards.

Thanks,

electrodog.

[ztu165]

Re: Philips 42PFL7422D backlight troubles

Guys the FETS on my inverters give me 8.40 ohms plus or minus 0.01 ohms except for one that gives me a reading of 8.36 ohms which is a drop of 0.04 ohms compared to the others. Someone mentioned the they should be 8.5 ohms, does this mean all of my FETS are bad? The inverters on the TV are not the original inverters and the TV does work but there is a very slight flickering on image noticeable specially on white image or TV menu. What do you guys think?

[tom66]

Re: Philips 42PFL7422D backlight troubles

Which way are you measuring?
8.5 ohm is very low for a FET but if that is the spec, then 8.4~8.46 ohm is good.s

[ztu165]

Re: Philips 42PFL7422D backlight troubles

Which way are you measuring?
8.5 ohm is very low for a FET but if that is the spec, then 8.4~8.46 ohm is good.s

I place dmm leads on fet pins with all FETS still in circuit but TV off.