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

in Troubleshooting TVs and Video Sources

05-10-2025, 03:23 PM
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...

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

in Troubleshooting TVs and Video Sources

05-10-2025, 02:52 PM
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.

[ATTACH=JSON]{"alt":"Click image for larger version Name:\tScreenshot 2025-05-10 at 4.49.00\u202fPM.png Views:\t0 Size:\t1.16 MB ID:\t3634253","data-align":"none","data-attachmentid":"3634253","data-size":"custom","height":"448","title":"Screenshot 2025-05-10...

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Last edited by KYBOSH; 05-10-2025, 02:54 PM.
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KYBOSH replied to Trying to Save - SONY BRAVIA KD-75X780F - No Picture BUT there’s sound

in Troubleshooting TVs and Video Sources

05-10-2025, 01:24 PM
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?...

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

in Troubleshooting TVs and Video Sources

05-09-2025, 11:35 PM
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.

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

in Troubleshooting TVs and Video Sources

05-09-2025, 07:11 PM
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...

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Last edited by KYBOSH; 05-09-2025, 07:15 PM.
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KYBOSH replied to Trying to Save - SONY BRAVIA KD-75X780F - No Picture BUT there’s sound

in Troubleshooting TVs and Video Sources

05-09-2025, 03:20 PM
Thank you for the clarification!
I jumpered both testpoints together and removed bother FFCs.
The voltages are exactly the same.
0V everywhere except L2 which has 1.1V.

I didnt bother testing with only 1 cable on given that result.
If you think i should please let me know....

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

in Troubleshooting TVs and Video Sources

05-09-2025, 02:49 PM
I mentioned that L2 (the large gray inductor) is measuring 1V.
I measured it against the ground of the screw securing the TCon to the chasis,...

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

in Troubleshooting TVs and Video Sources

05-09-2025, 02:41 PM
Just to be clear:
Step 1: with the power OFF, solder a thin wire between the two test points you illustrated in the picture.
Step 2: With the power ON, test for voltage at all the inductors with I) both FFC connected II) either L or R FFC connected and finally III) no FCC connected.

Is this how you want this experiment done?...

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

in Troubleshooting TVs and Video Sources

05-09-2025, 02:12 PM
Yes i have 12v+ on the fuse. It was my sanity check when i wasnt seeing anything on the inductors. This is the new TCon also. Amd the 2 processor chips there are hot....

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

in Troubleshooting TVs and Video Sources

05-09-2025, 10:27 AM
THANK YOU FOR THIS

This actually reminds me of the weird magnetic field - LED trick i discovered on Youtube and posted about.

I checked for voltages across all the inductors you marked and NONE HAD VOLTAGES except L2 (large gray one) and it was only reading 1V....

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

in Troubleshooting TVs and Video Sources

05-09-2025, 09:26 AM
Sorry [USER="71977"]nomoresonys[/USER]
Im currently looking for those test points.
Its not easy finding them... very tiny markings.[ATTACH=JSON]{"data-align":"none","data-size":"full","title":"20241119_150816.jpg","data-attachmentid":3633471}[/ATTACH]nomoresonys...

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

in Troubleshooting TVs and Video Sources

05-09-2025, 05:19 AM
Yes Sir I replaced both with brand new ones....

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

in Troubleshooting TVs and Video Sources

05-09-2025, 04:59 AM
Thank you Lotas. [URL="https://www.badcaps.net/forum/troubleshooting-hardware-devices-and-electronics-theory/troubleshooting-tvs-and-video-sources/3510688-trying-to-save-sony-bravia-kd-75x780f-no-picture-but-there%E2%80%99s-sound?p=3631250#post3631250"] I replaced them earlier this week[/URL] with brand new ones direct from Sony distributor (encompass.net).
Davi.p suggests that I am dealing with a mainboard issue.

I did some searching and found Nick's Electronics Repair (not to be confused with Nick's TV Repair!) [URL="https://nickselectronics.com/products/xbr-75x850f"]offers...

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Last edited by KYBOSH; 05-09-2025, 05:17 AM.
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KYBOSH replied to Trying to Save - SONY BRAVIA KD-75X780F - No Picture BUT there’s sound

in Troubleshooting TVs and Video Sources

05-08-2025, 07:07 PM
First off, thank you very much for explaining the screen tapping phenomenon. I usually don't feel like I have egg on my face but this YouTuber got me!

If the mainboard is the problem then I would have egg on my face again!. It gives sound get sound, response to input,ect, accepts firmware updates... everything that would indicate that its a good mainboard. Plus the troubleshooting flowchart (I posted above) for this model does not list the mainboard as even a probability at all.

But we have eliminated just about everything along the way so unless there is something...

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

in Troubleshooting TVs and Video Sources

05-08-2025, 02:19 PM
Here is a screenshot of the YT video i linked above. At the 20 second mark he demonstrates how the display is powered but with no image.

[ATTACH=JSON]{"alt":"Click image for larger version Name:\tScreenshot 2025-05-08 at 4.11.55\u202fPM.png Views:\t0 Size:\t2.18 MB ID:\t3632800","data-align":"none","data-attachmentid":"3632800","data-size":"custom","height":"290","title":"Screenshot 2025-05-08 at 4.11.55\u202fPM.png","width":"500"}[/ATTACH]...

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Last edited by KYBOSH; 05-08-2025, 02:22 PM.
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KYBOSH replied to Trying to Save - SONY BRAVIA KD-75X780F - No Picture BUT there’s sound

in Troubleshooting TVs and Video Sources

05-08-2025, 12:31 PM
I updated the post the data [USER="169795"]lotas[/USER] requested. But i think your low opinion of youtube videos and tutorials isnt quite right or fair. A lot of amazing and informative things there and im quite appreciative of the content creators efforts. Of course not everyone or everything is good on their but a lot of it is.lotas...

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

in Troubleshooting TVs and Video Sources

05-08-2025, 11:45 AM
I spot checked those already but using the ground from the chassis. but i went back just now to check again will check again (with the grounds you specified) and they are all showing as not shorted . I will post the resistances shortly.

Edit to Add:
The ones you asked to to measure show a resistance of 2.34-2.35MΩ on each of the legs of 6 legged SMDs (rectifiers?.
The 2 legged device reads 2.468MΩ.

Curiously on the panel board on RIGHT side, the same SMDs all read as OPEN (no resistance at all)....

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Last edited by KYBOSH; 05-08-2025, 12:46 PM.
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KYBOSH replied to Trying to Save - SONY BRAVIA KD-75X780F - No Picture BUT there’s sound

in Troubleshooting TVs and Video Sources

05-08-2025, 11:37 AM
I dont recall checking those before but I will have a look on my TCon to see if I can spot the test pads.
Another (seemingly sure fire) way i have seen on Youtube it to tap the blank screen when the power is on.
You will see flashes of white light pop up. I have done this and this TV responds in this way....

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

in Troubleshooting TVs and Video Sources

05-08-2025, 11:29 AM
Doing more reading I saw that the CKV lines short to their corresponding CKVB lines (CKV1 goes with CKVB1 and so on).
I figured I could go in and measure the resistance of the pair to see if I could at least get a clue about what might be happening.
This logic maybe completely wrong but I figured I'd see what I could see.

Conveniently the T-Con has a section of test points dedicated to the CKVs and CKVBs.

[ATTACH=JSON]{"alt":"Click image for larger version Name:\tScreenshot 2025-05-08 at 1.17.55\u202fPM.png Views:\t0 Size:\t293.3 KB ID:\t3632683","data-align":"none","data-attachmentid":"3632683","data-size":"custom","height":"500","title":"Screenshot...

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

in Troubleshooting TVs and Video Sources

05-08-2025, 09:49 AM
Definitely out of my league on this TV when it comes to shorts.
I'll wait to hear back from you guys who have experience with this.

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