Philips LCD TV - audio / no video

[swamper8]

Before swapping parts, I'm looking for confirmation on an issue I'm having with my mom's LCD TV:
Philips 40PFL3705D/F7
TV has sound.
TV has no video.

It is showing a BLUE screen, not a black or slightly glowing screen like other accounts I've read. It also does not show menus when requested by the remote.

It seems 9 out of 10 times similar issues are solved by replacing the T-CON board. (bad capacitors) The TV is several hours away so I cannot take the back off to confirm damaged caps.

Just looking for input on these specific set of symptoms (audio/blue screen/no menus) as to whether these are still symptoms of the T-CON PCB.
I will need to purchase it in advance of opening the TV up so I have the right parts on hand when I make the repair.

Thank you

[budm]

Re: Philips LCD TV - audio / no video

So you do have backlights and just blue screen but to image, that can be the T-CON, the main board not sending the signals to the T-CON, LCD panel problems.
You need to at least check and see if you do have DCV at both ends of the SMD fuse against the GND first, it should be either 5VDC or 12VDC depends on the panel.

[swamper8]

Re: Philips LCD TV - audio / no video

So you do have backlights and just blue screen but to image, that can be the T-CON, the main board not sending the signals to the T-CON, LCD panel problems.
You need to at least check and see if you do have DCV at both ends of the SMD fuse against the GND first, it should be either 5VDC or 12VDC depends on the panel.

I'm assuming since the screen is blue, the backlights are working.
Is this fuse on the T-CON board or is it on the main board? And what result would indicate what failure? EG what if I have voltage on both sides or what if I don't? I realize that if I don't have voltage on one side that would mean the fuse is blown, but for what reason.....main board? T-CON? LCD panel?

[swamper8]

Re: Philips LCD TV - audio / no video

I do recall at one point the TV may have been making an odd noise, like a chirp, but I cannot remember. I wonder now if it was a cooling fan going bad. If the TV does have a fan, I wonder what it was cooling? (processor on main board?) That would lead me to suspect the main board. Guess I'll have to take it apart to diagnose first......

[budm]

Re: Philips LCD TV - audio / no video

The T-CON board has SMD fuse. If it has blown fuse then you will see 5Vdc (or 12V) on the input side of the fuse only otherwise it should show 5V on both ends of the fuse with ref to GND.
The fuse may have blown due to just bad fuse (the fuse is subjected to surge current when the Voltage is sent from the main board to run the T-CON), or failed component on T-CON or in the LCD panel.

[swamper8]

Re: Philips LCD TV - audio / no video

Ok, I finally have the TV in hand. Pulled the back off. Found the T-CON PCB. Appears to be 6 total PCB's. Found the SMT fuse near the LVDS connector on the bottom of the TCON PCB. Measured 3.3V on both sides of the fuse. Also rang out fuse with my meter. I inspected the main PCB and T-CON CAPS and I see none which are bubbled/leaking etc. Should I pull the metal shields off the other two PCB's and inspect them as well? My mom said the screen is blue, but it's actually dimly lit black. I can see that all of the back lights are ON. Again, sound but no video and no menus show up either when the menu button is pressed.

Should I still suspect the T-CON PCB? There's another PCB that is between the T-CON and the HDMI port PCB. It is BA01P2G0404 1_A and it's called an frc CBA PCB. I guess maybe it could also be the LCD? If there's any other diagnostic steps I can take before throwing parts at this I would appreciate the help.

EDIT:
I see some CAN/CAP metal polarized caps near the LCD ribbon cables. Are these the caps that typically fail? I have the capability to replace those at work.

[budm]

Re: Philips LCD TV - audio / no video

3.3V for running T-CON is way too low, never run into one with that low of the Voltage. Are you sure it is not an error in measurement? You measure it using chassis as the GND ref and check the Voltage on each end of the fuse?
Pictures of the board and the fuse?

[swamper8]

Re: Philips LCD TV - audio / no video

3.3V for running T-CON is way too low, never run into one with that low of the Voltage. Are you sure it is not an error in measurement? You measure it using chassis as the GND ref and check the Voltage on each end of the fuse?
Pictures of the board and the fuse?

Yes sir, black probe to metal chassis/plate and red probe to each side of the pictured fuse. I measured 3.3ish. (both sides of fuse) Because this specific T-CON is so hard to find I jumped on the only one on EBAY.

These are shareable links to the photos, if I want to display photos here i have to upload them somewhere like photobucket and it's a PITA

https://drive.google.com/file/d/0ByK...ew?usp=sharing

https://drive.google.com/file/d/0ByK...ew?usp=sharing

[budm]

Re: Philips LCD TV - audio / no video

That is not the fuse, that looks like some kind of the ferrite bead inductor, the fuse is right there inline with the fuse designator F100 printing, and one end of the fuse is connected to large copper pad that is connected to five pins of the LVDS connector, the large pad has 51 printing on it.
BTW, the resistance of the fuse and the ferrite bead inductor should have <1 Ohm.
If you do have 3.3V at the fuse, it is more likely there is problem on the main board that is not supplying the correct VDC to run the board.

[swamper8]

Re: Philips LCD TV - audio / no video

Ok so one side has 12vdc and the other has 3vdc. One side is connected to that ferrite bead. 12v is on the LVDS connector side of the fuse.
Do you know the rating of this fuse or what a good rating would be to replace it with? Is this fuse slightly undersized from the factory or should I suspect a problem elsewhere in the TV has caused the fuse to blow? I have access to SMD fuses at work.

[budm]

Re: Philips LCD TV - audio / no video

Are you talking about the correct fuse now, not the one you pointed to, right?
The rating of the fuse is printed right on the board next to the fuse, 3.15A 32V minimum Voltage rating. You can try using regular 3A fuse with leads on each end just for testing, 3A car fuse will do.

[swamper8]

Re: Philips LCD TV - audio / no video

I will replace it with the correct fuse, I can rework this under a microscope. If I have to order the fuse from digikey I'd also like to order any other possibly faulty components all at once. (Caps etc) nothing like ordering a 8 cent fuse and paying $12 shipping. So any suggestions for other components would be appreciated. I can replace everything but BGA's.

[budm]

Re: Philips LCD TV - audio / no video

I will try using temporary fuse first to see if you will get the pictures back.
i use PICO II fuse with legs, just have to bend the legs.
http://s807.photobucket.com/user/bud...?sort=3&page=1

[swamper8]

Re: Philips LCD TV - audio / no video

so I didn't have the correct SMD fuse, but I got a pico on there. Video came right up, menus work etc. So the problem was the fuse/T-CON PCB. want to order the right fuse tonight. Now should I consider replacing any other components? Should I move the fuse up slightly in amperage?

[budm]

Re: Philips LCD TV - audio / no video

So was the old fuse tested as open circuit or it shows some resistance > 1 Ohm? I would stay to the same rating, it can be just bad fuse that failed due to surge current when power is applied. If you look at the spec of the LCD panel it will give you the surge current and the running current of the T-CON.

[swamper8]

Re: Philips LCD TV - audio / no video

No I didn't test the old fuse. Just pulled it off and soldered the pico in its place. Thanks for your help on this. I'll probably just replace the fuse with a identical one. If the fuse should clear again I may think about bumping up to a 3.4A. I'm assuming this is a fast blow? I looked on digikey and they actually make slow-blow's that tiny. Maybe a slow blow would be a better choice?