Sony no image, no sound and no standby flashes

[Danga]

Well, for all the LCD TV Repairing masters.
I've a LCD TV with the following symptoms:
- No StandBy flashes, just Green Power Led steady as normal
- No image, no backlight and No Sound. Even by changing input, volume, channels. Even by trying to enter service mode or whatever
- I isolated the PSU and tested it and it gives all the voltages
- Also, I isolated the Inverter and just by connecting it with the PSU it works properly illuminating the lamps

By measuring I've found:
- BL-ON, TCON-ON, DIMMER are 0V
- BL-ERR is 3V (but the Inverter don't use it)
- TCON-12V do exists properly if I set TCON-ON. But I tested it without connecting the TCON board

I inspected all the boards (PSU, Inverter, Main, TCON) and there are no blown/bad components or fuses.
So I think that can be the board, unless there are some kind of protection that I didn't check. The only place that I've not seen is under the cooler (I think the main cpu).
I want to repair the board cause till now I didn't get a new one, and because I want to learn something.

I've good electronics and repairing background, but this is my first LCD TV repair attempt.
It is a Sony Bravia KDL-40EX407 with 3 years of normal use. The best schems what I found are KDL-40EX500 and KDL-32EX302.

A curiosity: by following the traces of TCON-ON it seems that the signal have to come out from an AND gate being one input HI from microcontroller but the other input LO cause there is nothing more connected than a resistor o capacitor (I didn't identify it) to GND. I don't know if somebody have traced the proper origin of TCON-ON.

[kenny1070]

Re: Sony no image, no sound and no standby flashes

Reconnect everything and retest the power supply voltages to the main board - stand-by , regulated and un-regulated vdc (typically about 3.3 , 10 , and 18 vdc).
Do you hear the main relay click when the set is first plugged in ?
Do you hear the power-on relay click when the set is turned on?

With the absence of sound and backlight - it sounds more like a command
"power-on" problem.

I can't find a schematic for this model - and without pictures it is very hard to help.

But try these suggestions and let us know what you find.

[kenny1070]

Re: Sony no image, no sound and no standby flashes

While the TCON board will handle pixal configuration (how it actually looks on the screen) -

The sound , backlight , and actual video signal itself are usually delivered from a different area of the system - for example:

- A/U board (or a/v)
- Main board ( or b/u)
- Inverter board


Hope that helps

[Danga]

Re: Sony no image, no sound and no standby flashes

I reconnected everything and tested it:
The result is "no relay-click sounds" and the voltages as I said before, that is STBY,ACOFFDET,PWRON,BL-ERR=3.3V
BL-ON,DIMMER,TCON-ON=0V
12V and 24V are fine

[capkid]

Re: Sony no image, no sound and no standby flashes

Sonys are known for panel and main board issues. There are people who repair them, but I'm not sure if a BGA or some other component goes bad or detaches.

[Danga]

Re: Sony no image, no sound and no standby flashes

I found that schematics of KDL-40EX500, KDL-40EX400 or KDL-32EX302 are similar to my KDL-40EX407

[Bob Neely]

Re: Sony no image, no sound and no standby flashes

I am having a problem with the KDL-40EX500. I found a burnt cap C6332. Can you tell me on the schematic what the value is and if there is another one on the board? Thanks for any help.

[CHOOKY]

Re: Sony no image, no sound and no standby flashes

Hi l have a LG 50PG20D, no sound no picture. screen goes grey then switches off 3 times. Over time got worse took a while to go on .......now no sound or picture anymore. LG repairer could not fix it no parts he said it could be EBR42472903/EBR42472802 don't know if he is right because he could not get the part to try. Can l fix the problem myself. Have looked around can't find anything burnt out.
Would appreciate help Thanks....don't have a TV to watch now

Thanks from Chooky in Australia