Philips 58PUS7555/12 backlight only

[domix]

Yes i have all, only i dont have thermal camera

[lotas]

There are usually 2-3 protective diode assemblies at the ends of the buffer strips, and these are where breakdowns occur. You can take a photo of these strips.

[domix]

I found one cat phone with flir camera

[lotas]

This CHOT panel doesn't have them. The circuitry is different, so check the passive components (capacitors, MOSFETs, etc.) on these buses. If there's no short on them, the problem is with the panel itself.

[Davi.p]

Manufactures recommends not to supply any current to the supply lines of panel before the vcc is turned on, this will bring to a non recoverable damage (i did it in early days and ruined some traces on a tab) , i have already explained how short can be searched, or with a 100/1000th ohm meter, this is the basis from what i read, every tcon has a different precise timing where the supply lines appears. After this,.48ohm do not resemble a short.. a short is usually less than 1 ohm. Bye.

[tom66]

48 ohms could be a failure on the panel ICs or it could be a failure on the board. Ceramic caps can and do fail "leaky".

Without being able to detach the panel there is a risk of damaging it but I would still try since there is not much to lose if the TV is already broken.

I would apply 2-3V at current limit 500mA across the VAA supply and see what gets warm, you can carefully use freezer spray or isopropyl alcohol to help, as they will evaporate if the components get hot. Thermal camera makes it even easier.

[Davi.p]

I noticed only now the last page posts.. well, this chot is the new fashion of poop tv sets where half tcon circ. is on the tcon board or main b. and half is on the strip boards, this from the pitctures appears has two twin chips for the gamma control, i know gamma control uses VAA to generate gamma levels, my bet is that some discrete or the chip themselves for the gamma circuits are at fault, so check every discrete first, those 0 ohms etc...

[domix]

How to do that?
I would apply 2-3V at current limit 500mA across the VAA supply and see what gets warm, you can carefully use freezer spray or isopropyl alcohol to help, as they will evaporate if the components get hot. Thermal camera makes it even easier.

Which one is this chips
my bet is that some discrete or the chip themselves for the gamma circuits are at fault, so check every discrete first, those 0 ohms etc...

[Davi.p]

3rd photo

[tom66]

How to do that?
I would apply 2-3V at current limit 500mA across the VAA supply and see what gets warm, you can carefully use freezer spray or isopropyl alcohol to help, as they will evaporate if the components get hot. Thermal camera makes it even easier.

Solder wire to VAA test point which is your positive and a wire to the ground on the T-con board which is black.
Power to the TV should be OFF, disconnect T-con from everything except the panel ribbon with the 48 ohms short.
Connect power supply (ensure polarity is correct) set voltage very low max 1V, set current limit to 500mA, increase voltage and start looking for warm spots. If nothing happens ramp up to about 3-4V, max 1A. You should be able to find the short at that point.

[domix]

I solder a wire and connect 1v 500ma to tcon. I get one spot hot on lcd stripe on 512 resistor.

all with 0ohm has on multimeter 0ohm.
and all smd with 512 writen on it has 2,55kohm

[tom66]

Could be the chip next to it, are you sure thermal and visible are lined up as those FLIR cameras require you to adjust the alignment for each viewing distance usually.

[Davi.p]

The finger! The finger! I will never manage to understand how can be so convenient to buy a FLiR for such a rubbish electronic sets..

[domix]

I think it was aligned yes.

I didnt buy flir camera, i found old CAT phone wit flir camera in garage.

[tom66]

Well I suggest double checking with freezer spray or alcohol.

[Diah]

safe the forum from rubbish test suggestion ... sorry guys ... read my post #15

[domix]

safe the forum from rubbish test suggestion ... sorry guys ... read my post #15

Okay, I'm going to drop the project,, I believe it's true.

[Random Bloke]

Look at C111, its cracked.

[Davi.p]

Yes, it seems so... try replace it with a 20uF 50v, if you have only 10uF try it

[notallbad]

maybe try isolating one pin at a time on the tcon ribbons to panel until image appears then inspect image to determine if the picture quality remains acceptable.