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main board reset periodically

The issue start with horizontal lines on the right side of the screen and after a few off/on and reset, there is nothing, no sound or picture. I opened the back of the tv and notice the main board would reboot every 90s or so. Even with all cables disconnected (except for power signal and the one to power supply), it reboots every 90s. Is this an indication of a bad board or it reboots because of no load? When things are connected, it reboots because of other things cause it to reboot?

Here is some voltage measurement on the connectors

CN201

pin 1, 5-7, 10-15: 0V

pin 2: 3.81V

pin 3: 5.11V

pin 4, 8, 9: 12.66V

CN301

pin 1,2, 9-14: 0V

pin 3-8: 24V

CN203

pin 1-7: 0V

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Tri Le exactly what do you mean by reboot? What model is this?

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It's a Vizio P702ui-B3. I see the LED on the board goes off and on. To confirm I put a probe one the 5v ps-on pin and saw it goes to 0 and back to 5 about every 90s

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Tri LE it’s a bit confusing. The pin you are talking about would be on CN201 pin #3 which turns the power supply on. If it gets signal but does not turn on it is most likely a bad power supply. Check the other voltages on CN201 and CN301 and let us know what you got. It will also help if you post some pictures of your boars and point out where you measure and which LED is blinking. It is possible that it just shows that it is sending a signal/trying to connect etc.

Both main and power board for this model are pretty much unavailable at the common places. That tell me that there are some issues with those boards. You can get repair kits for both boards to replace the most commonly failed components. you may need to consider something like that.

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Thank you so much for your help. I edited the original message to include voltage measurements and some pictures. Please let me know if you need anything else to narrow down the cause

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It turns a few things on ... I know for sure it turns on the 24V on CN301 and the USB power and optical audio output on the main board. I do not have power to T-CON. I thought it was power supply board as well until I notice the main board rebooting

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Remember that the main board is turning on the power board. So if the power board does not respond to the main board it cold be trying to re-establish "communication"

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The t-con portion is not on. Do you know what's responsible for turning it on?

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So you get no power on the fuse of the T-con board. Should come from the main board but if your power board does not turn on you will also not get power to the T-con board.

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Tri Le will be eternally grateful.
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