Philips 42PFL7662d/12 problem: backlight?

[koektrommeltje]

Hi

I'm in need for some help to repair a Philips LCD TV which isnt functioning like it should: no video, no backlight. The only thing i can do is switch the tv on and off..

The television:
Philips 42PFL7662d/12
LC420wu5

The problem:
Well, the only thing i see is a black screen. No backlight, not even one second

What have i done allready?
I googled, found out that this particular tv has bad inverterboards. Swapped the BD9897FS chip on the masterboard, checked the fuse on it, checked the SK4075 mosfet's but no result.

I ony swapped the BD9897 chip, even though there was no visible damage to be seen. Someone told me that the LED on the masterboard inverter should ligten up when that IC is ok but even with a new BD9897 IC mounted that wasn't the case. No LED visible on the inverterboard

No backlight visible, not even a single flash
When disconnecting the slave, i also get no result. Still defective the inverter masterboard?

What do i want?
Save this television from the junkyard. And therefore, i can use your help!
Anyone any idea what the solution is to this problem?

And, how i can be sure that it's the inverterboard that cause theses problems? Maybe it's something else?

(The PSU isnt the problem i think. It's all rubycon caps that are on it. I measured the fuses, diodes and all OK.


Anyone any idea how i can solve this problem?



Thanks in advance!

[drpj23]

Re: Philips 42PFL7662d/12 problem: backlight?

Pictures are nice (using manage attachments feature).

Caps and the HV transformers can also go out on the inverter board (or are at least common)

I suppose you can verify that all voltages from psu are correct. There is probably a BL_ON pin on the inverter, if so, what's the voltage on that pin?

So you you can't even see an image (such as a menu) with a flashlight?

[budm]

Re: Philips 42PFL7662d/12 problem: backlight?

Yep, good clear pictures of the all the boards will be big help.

[koektrommeltje]

Re: Philips 42PFL7662d/12 problem: backlight?

I will take some pictures of the televisions inside later this day and put them here.

I can't see any video. Using u flashlight isn't showing anything on the screen as far as i can see.

From the master inverter i swapped one capacitor, but the other one is ok. I'll swap that also later on. That's not the problem.

No.. the only visible thing i can do is putting the tv on and off with the standby button. And then i can see the red LED on the front of the tv.

[selldoor]

Re: Philips 42PFL7662d/12 problem: backlight?

Please can you update your profile with at least country and mains voltage.
Did you test with a source - dvd player or something -was the sound working?
There is arepair kit for the inverter board - a bad sign as it suggests it is a common failure- it includes an ic with lots of legs - so not easy to remove/replace.

[koektrommeltje]

Re: Philips 42PFL7662d/12 problem: backlight?

https://cdn.badcaps-static.com/pdfs/...43f0f20fec.pdf
> The link for the modification for the specific inverterboard as advised bij Philips.

Im from the Netherlands and here the electricity is 230V.

Anyway, problem is solved at the moment. Only thing to do is the modification from the link here above so that it won't come back.

I only replaced the BD9897FS driver IC and programmed my logitech harmony for this device and pushed some power on/of buttons (after i swapped the bd9897fs chip. That made the blue led appear at the front of the tv.. the backlight lighted up and...it worked again.

Later this day, i'll upload some pic from the inside of this television.



I replaced the BD9897FS quite simpel. With a sharp Stanley knive i cutted the pins. Then removed the body, put some flux on the pins and removed these pins on the board with a soldering iron with a little bit of solder on it. Then resoldered the IC. Again with a lot of flux and with a little bit of solder on the tip gently touching the pin with the corner of the tip from. No problem

[selldoor]

Re: Philips 42PFL7662d/12 problem: backlight?

I dont follow - what happened between

"What have i done allready?
I googled, found out that this particular tv has bad inverterboards. Swapped the BD9897FS chip on the masterboard, checked the fuse on it, checked the SK4075 mosfet's but no result.

I ony swapped the BD9897 chip, even though there was no visible damage to be seen. Someone told me that the LED on the masterboard inverter should ligten up when that IC is ok but even with a new BD9897 IC mounted that wasn't the case. No LED visible on the inverterboard "


And it working?

[koektrommeltje]

Re: Philips 42PFL7662d/12 problem: backlight?

I dont follow - what happened between

"What have i done allready?
I googled, found out that this particular tv has bad inverterboards. Swapped the BD9897FS chip on the masterboard, checked the fuse on it, checked the SK4075 mosfet's but no result.

I ony swapped the BD9897 chip, even though there was no visible damage to be seen. Someone told me that the LED on the masterboard inverter should ligten up when that IC is ok but even with a new BD9897 IC mounted that wasn't the case. No LED visible on the inverterboard "


And it working?

What i did between? Nothing, except that i programmed my logitech harmony remote control for this television and pushed some buttons and then there was power: the blue led on the front of the tv lightened up, the backlight went on.

Obviously there are two ways to power on/off the television. One standby (red LED), one compleet no voltage i think? It wasn't mine tv, so i didn't know that and ik didnt have the remote for it. But, i powered it on.. which wasn't the case earlyer obvious :X

Looking at the repair: I've only swapped the bd9897fs on the MASTER INVERTER (and unsoldered en resoldererd the sk4075 mosfet. Didn't swap them.

Later i'll add pics. I made them, but can't find the cable to upload them.

[koektrommeltje]

Re: Philips 42PFL7662d/12 problem: backlight?

And it failed again... worked some week or so

What could that be? I only swapped the BD9897FS and made the modification as listed in the link from Philips.

How come this driver IC fails again? Is that because of bad mosfets?

[koektrommeltje]

Re: Philips 42PFL7662d/12 problem: backlight?



The master inverterboard. I swapped the BD9897FS driver IC and then it worked. And failed some week later or so.

The modifications with the resistor, capacitor and the 33v zener diode 33 are also visible on it.
The 33v is a normal zener diode.. although it should have been a 33V TVS Zener. That shouldn't be a problem i was told. Is this true?



The slave inverterboard at the right side.



And a picture with the master inverterboard left.



The slave inverter isn't updated by the way. If this one fails and the master is OK. I suspect to halve a half screen? Correct?

[budm]

Re: Philips 42PFL7662d/12 problem: backlight?

"The slave inverter isn't updated by the way. If this one fails and the master is OK. I suspect to halve a half screen? Correct?" Is that what you see before the screen goes black. The MASTER/SLAVE work like push-pull so both of them have to work, otherwise it will go into shutdown. I use 33V 5W Zener on my mod, so that is not the problem. I modded both of my boards.

[koektrommeltje]

Re: Philips 42PFL7662d/12 problem: backlight?

"The slave inverter isn't updated by the way. If this one fails and the master is OK. I suspect to halve a half screen? Correct?"

Is that what you see before the screen goes black. The MASTER/SLAVE work like push-pull so both of them have to work, otherwise it will go into shutdown. I use 33V 5W Zener on my mod, so that is not the problem. I modded both of my boards.

Well, at the moment i don't see a thing on the screen. I repaired only the master. Some days later, the TV was giving the same problems. At the master inverterboard i only swapped the db9897fs chip and unsoldered and resoldered the sk4075 mosfets after having them checked. It worked then... for some days.


I've order new parts; going to replace the BD9897fs again on the master and also go change all the sk4075 mosfets. After that i'll mod the slave board completely.

I'm not sure, but i think i used 1.3W 33V zeners. Can't tell you if these failed after repairing but it has worked afterwards.

[koektrommeltje]

Re: Philips 42PFL7662d/12 problem: backlight?

Today i replaced all the MOSFETS and the BD9897FS again on the master. After that it played again.
I assume the MOSFET were faulty on the masterboard. Again: no visible damage to the bd9897fs

I also replaced the MOSFET on the slave, just in case. Want to do the other modification on the slave, but i forgot to buy the 4.7ohm resistors :X so i can't complete modify it.

Question:
-will that be enough, or do i really modify the slave complete?
-if it start up again, is there any necessary to swap the slave bd9897fs on the SLAVE?

[budm]

Re: Philips 42PFL7662d/12 problem: backlight?

I would mod the slave board also, you also should replace those two lytics caps on both boards. The IC is usually damaged by the shorted out MOSFET between the Gate and Source pin. My TV is still running and I hope Philips is correct about this mod ii that tehy released since mod i dd not fix the blow up problem. The Zener is to Clamp down the 24V feeding it since when power supply is turn on, it does put on high voltage spike, that is why they want to clamp it down to around 33V. I believe the max VCC for the IC is around 35~40V.

[koektrommeltje]

Re: Philips 42PFL7662d/12 problem: backlight?

So it's not necessary to swap the bd9897fs IC, since i've swapped the slave mosfet even though it was working well.

I'll modify it further more; will buy the resistors so i can complete the modification on both boards.

[Schorsch87]

Re: Philips 42PFL7662d/12 problem: backlight?

I had the same problem with mit 42PFL7662 TV. I changed out the ICs, checked the mosfets and did the modification. Now the TV starts, backlight turns on but only for 1-2 seconds. While the backlight is running I hear a high/shrill noise from the inverter transformers. What could cause this symptome?

[MatBov]

Re: Philips 42PFL7662d/12 problem: backlight?

I had the same problem with mit 42PFL7662 TV. I changed out the ICs, checked the mosfets and did the modification. Now the TV starts, backlight turns on but only for 1-2 seconds. While the backlight is running I hear a high/shrill noise from the inverter transformers. What could cause this symptome?

Hi, I've the same problem. The backlight turns on during few seconds. During this time, I've also this noise.
Do you find a solution ?