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HISENSE RSAG7.820.1569 PSU issue, tv comes on for about 20 seconds then switches off

Good day. I am trying to repair the power supply for HISENSE RSAG7.820.1569. The TV just went blank but there was still sound. So I torched the screen and saw that the  picture was there but no backlight. I replaced the KA7500 which is the driver IC. Now the TV comes on for about 20 seconds then switches off. 
Please help

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Shizo
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Hello
Try to disable inverter protection:  pin13 connect with pin14-, then from this point connect  10kΩ to pin2 (This I try in Fujitsu-Siemens monitor)
I think you checked secondary ELKO-s before when replaced KA7500..

If you hearing  CCFL arcing, then must disconnect this bad CCFL lamp.
   

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Happiness
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@Shizo
Thank you for suggestion. I did isolate the protection circuit and the TV came on for much longer. However after a few minutes i smelled something burning and found that the Mylar cap across the HV output was the culprit. 
I am waiting for the replacement part and I will report back once I got the TV working again 

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Happiness
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@Shizo Thank you very much for your help. I tried as you suggested and now the TV was not going off after a short while. However, I started to smell something burning. After a quick investigation I found that a cap, 10p 6kV that is across the HV output was getting hot. I guess it is this cap that was sending an error message back to the PWM chip. 
Tomorrow I will replace the cap and I will come back to report my success or failure

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