Trying to Save - SONY BRAVIA KD-75X780F - No Picture BUT there’s sound

[lotas]

Strange, check the same on the second T-con. Measure the resistance on the inductors relative to ground, there should be no low or short resistance, except for the one that sits on the ground, to convert the negative voltage relative to ground (VGL).

[KYBOSH]

Strange, check the same on the second T-con. Measure the resistance on the inductors relative to ground, there should be no low or short resistance, except for the one that sits on the ground, to convert the negative voltage relative to ground (VGL).

Sorry for the delay my friend!

It was next to impossible measuring the resistance of the smallest inductors because the leads are on the bottom and not on the side.
Some of the inductors had wandering resistance readings but they eventually settled on a number. I indicated that with a ⇅ symbol.

These readings were are basically the same whether I was testing the TCon on the TV or the one that I have off the TV.
Hope these are of help. To be honest I am not sure what they mean. I assume the wandering resistances are due to the nearby capacitors.
I used the copper mounting pads as my ground while measuring resistance.

[KYBOSH]

Funny story... i was looking over the old LVDS cable and noticed that the copper tracks at the end looked kind of dull.
Upon further inspection i found that it was covered with scotch tape.
Apparently the previous owner attempted to mask off 90% of the traces with tape in an attempt to get the TV working.
Would have never noticed this if not by chance.

[Davi.p]

quite irrelevant, but if you wish to play and experiment a bit i can suggest you a 5 min. test, locate the quartz near the cpu, solder a thin wire to short circuit it, connect everything and see if the screen auto test begins.. this could be the same as running the screen alone but here we can see 1. if screen works, 2. if half of tcon is on the MB.. kindly it will not work because of bad main board, but lets see..

[bohaboha]

quite irrelevant, but if you wish to play and experiment a bit i can suggest you a 5 min. test, locate the quartz near the cpu, solder a thin wire to short circuit it, connect everything and see if the screen auto test begins.. this could be the same as running the screen alone but here we can see 1. if screen works, 2. if half of tcon is on the MB.. kindly it will not work because of bad main board, but lets see..

Davi.p can you please point out where the tests should be carried out

[Diah]

what had SoC to do with quartz Hz, at time each SoC had his own Hz tact.

[KYBOSH]

quite irrelevant, but if you wish to play and experiment a bit i can suggest you a 5 min. test, locate the quartz near the cpu, solder a thin wire to short circuit it, connect everything and see if the screen auto test begins.. this could be the same as running the screen alone but here we can see 1. if screen works, 2. if half of tcon is on the MB.. kindly it will not work because of bad main board, but lets see..

Davi can you give a primer on how this test method works? This is actually my first time of hearing of any diagnostic test dealing with that timing crystal.
If the MStar chip is not able to send a video signal how will this force it to do so?

[Davi.p]

No...this test is a step back when i was suggesting the screen self test, we are not sure about the bad tcon circuitry, with this test you can see if all part related to screen is ok, then the other part, the processor would be not ok.. disabliing the quartz is disabling the processor, so like detaching a main board from the screen

[KYBOSH]

No...this test is a step back when i was suggesting the screen self test, we are not sure about the bad tcon circuitry, with this test you can see if all part related to screen is ok, then the other part, the processor would be not ok.. disabliing the quartz is disabling the processor, so like detaching a main board from the screen

Interesting...
Okay so be clear:
With the power off/unplugged, I want to create a short as illustrated in the picture.
Then power ON/plug in the TV and check for a self test pattern on the screen.




This scenario is the perfect reason why buying a TV160 4K-Vbyone & 2K-LVDS Screen Tester would be warranted! Its on my wish list!

[Davi.p]

the oscillator is not that, watch the processor, less than a inch down there is a grey 4 pin smaller one, don't; ask me the pinout, i do not know... the rest, thermal camera, special testers, im sure you don't last in the repair market witth these purchases..

[KYBOSH]

the oscillator is not that, watch the processor, less than a inch down there is a grey 4 pin smaller one, don't; ask me the pinout, i do not know... the rest, thermal camera, special testers, im sure you don't last in the repair market witth these purchases..

I dont see anything like what you are describing but its probably all well and good.
This experiment is probably way over my head anyway!

Im going to go with the assumption that the Mainboard is the issue.
If I send it in for repair and its NOT the issue then at least for a $30 bench fee I will have confirmation that it works.
And that'll just leave the panel as the only possibility.

Im not in the repair market. I do this for a hobby and quite enjoy learning.
A tool like the TV160 is probably worth it bcos it will save someone days/weeks/months running around trying to figure these things out.

[bohaboha]

this guy hobby always smoke & BBQ, what had SoC to do with quartz Hz, at time each SoC had his own Hz tact.

it is so

[lotas]

Check these fuses just in case.

[Davi.p]

My balls full with the elment here over, another reporting to the staff, i see people following him, keep him if you like, i seen him never fixing any product... anyway..

this is the item..

i don't kmow what do you mean for "hobby" , didn't you sell your works?

[nomoresonys]

It's actually a compliment to you Diah, the little guy is intimidated by your knowledge.

[Davi.p]

kybosh if you want i can suggest you things in private, not here in middle of --------.. people here are continuing to trespass the technical questions, especially by sunday when staff is on rest, typical cleverness of the useless unfair elements..

[Document Archive]

Davi.p - I agree with you the comments against your post are uncalled for so I will put in a ban for the user if it persists. However, you need to have a thicker skin as they remarks are quite tame. You can just ignore or say you dont respect them. At the end of the day we see you as a valuable contributor to the site so you should not let one person put you off from stating your opinion here. Zero tolerance to any bullying and admins are watching closely

[KYBOSH]

Hello everyone. Hope you are all well and in good spirits.
I wanted to update this thread with information that I have found since I last posted.

I found a good guy on ebay who agreed to test the mainboard for me for a bench fee.
He told me initially that these TVs are known for their panels dying but I wanted to be absolutely sure it was the panel and not anything else since we have been working on this thing for several months.
So he agreed to test it for me by putting it in another (similar but not same) TV model. Still dont know what model TV he used as I thought these mainboards were quite specific to the models they were made for.

Anyway the mainboard is fine and he was good enough to send pics as proof of life.
So Im at the end of my journey with this set.
I may never be good enough to do short detection and remediation on these LCD panels.
And even if I eventually could I certainly cant do anything like that now.

Thank you all for your help, input and expertise. I learned a lot and enjoyed the experience.
Hope this helps the next journeyman who has the same or similar symptoms.

[Davi.p]

if you haven't tried another tcon, for a so large tv set i would try one..

This phantomatic "good guy" has really tested the main board? Where are the proofs?

[KYBOSH]

if you haven't tried another tcon, for a so large tv set i would try one..

This phantomatic "good guy" has really tested the main board? Where are the proofs?

Thank you for the input Davi.
You may recall a few pages back I ordered a brand new T-Con board but there was no change.
The "good guy" sent me proof by way of a screenshot (not posted) of set's serial number located in the System Information page (and they match 👍).

No one wanted to fix this set more than I did but according to the Troubleshooting flow chart there is nothing left but the panel that could be at fault.