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-SOLVED- SONY KDL-32EX600 red led 2 flashing - negative 120V backlight missing PSU GE3D APS-272

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kicku

Hello
I have on my table this sony kdl32ex600 with backlight issue. It's a common failure of this psu but i do not find any part faulted on this board.
The schematic it is almost the same, with minor differences with GE3B found at page 56 on this service manual:
https://elektrotanya.com/sony_kdl-32ex600_kdl-40ex600_kdl46ex600_chassis...
Uploaded only the page 56 from this sm to easing the search.
The red led it's flashing 2 times, meaning psu faulty. Indeed the led backlight does not light.
With the PSU outside of the tv, just with one resistance of 180ohm between standby ( pin 1 3,3V on connector CN6150 ) i get this values
on in:
starting with pin 1

1  +3,3V ST-BY
2  +3,3V AC_OFF_DET
3  +3,3V POWER_ON (with resistance 180ohm between pin1 and pin 3)
4  +12,56V AUDIO_12V
5  0V AUDIO_12V_GND
6  0V REG_12V_GND
7  0V REG_12V_GND
8  +12,6V REG_12V
9  +12,6V REG_12V
10  +0,1V BL_ERR
11  +3,3V BL_ON
12  0V DIMMER
13  0V DIMMER_DC
14  0V T-CON_Vcc_12V
15  0V T-CON_ON
All measure done at secondary ground point C6800 GND as reference.
Meanwhile, the led connected to CN6800 will remain with no light at all. The CN6800 will deliver positive 91V.
The negative branch will deliver at CN6801 ( both pin1 & 2 ) just -1V.
In the training manual found always in here at
https://elektrotanya.com/sony_kdl-32ex600_40ex600_46ex600_chassis_az1k_t...
at page 56 will say "SHORT" at pin 12 DIMMER for testing the PSU, always with pin 3 POWER_ON connected to 3,3V ST-BY - pin1.
If i'll put a 180ohm resistance between GND and pin 12 DIMMER, then the tension on CN6800 will rise to +179V and the negative from the CN6801 will rise to -5V, the backlight led will light very very weak.
All tension from CN6805 will remain the same, except the BL_ERR will rise from +0,1V to +1,1V.
With only power_on pin 3 shorted by 180ohm resistance to the pin 1, i get this weak oscillation at emiter of Q6816 + Q6817

[URL=https://picturepush.com/public/16067400][IMG]https://www1.picturepush.co...

With pin 12 DIMMER shorted ( always by a 180ohm resistance ) at GND, the oscillation will change from 250khz 1,6vpp to almost 70khz at 0,81Vpp. as below:

[URL=https://picturepush.com/public/16067401][IMG]https://www1.picturepush.co...

Already checked the capacitors C6828 / C6830 together with D6805 / D6806.
Also checked the L6800 ( trafo ) and i've get 5,5mH instead of 5mH, i think it's ok.
All fuse checked, ok.
Q6814 and Q6801 tested under mosfet tester, ok.

[url=https://picturepush.com/public/16067402][img=https://www1.picturepush.co...

IC6800 & IC6801 gave +9V and respectively +2,49V

Already checked various components all over the board, i am out of ideas.

Any idea or help would be apreciated.
 

File attachment: 
Comments
kicku

Solved.
The PSU it's ok, has nothing faulty on it.
If puting the BL_ON at +3,3V with a resistance of 180ohm between them and DIMMER also to +3,3V always with another 180ohm resistance, then, the oscillation on Q6816 emiter will grow to almost 4,8Vpp. This will lead to almost -120V on CN6801 and almost +100V on CN6800.
So, the PSU it's running fine as it should. It turned to be the mainboard faulty. Simply does not see the +12V audio branch and here it's why.

The +5V branch is in short to GND. The two regulators IC6002 and IC6003, were fine. Also the IC6007 that will take 5V input to deliver +1,8V.
At this point i don't find the service manual for this mainboard: E1767069D
Did not find yet the schematic but the pcb is almost as this one
sony_kdl-32_37_40_46ex402_chassis_az1-n found in here, on elektrotanya.
At this point i can say the 2 flashes that red led will do is because the main board does not see the +12V branch, not because the PSU is faulty.
For me it's solved.

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Cyrix
Cyrix's picture

Maybe changing the PSU board resolve your problem. 
If you have a reserve PSU from a friend you will quickly find out the problem. 
Good luck.

Best regards,
Cyrix​

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kicku

Thank you for this idea.
I want to resolv the problem on this psu. Buy it will not help me to understand why / where / how it's not working.

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