SUMMARY
======
This is a Vizio VO42L. It won't power on. When the TV is first plugged in the VIZIO logo should be orange. When the TV is turned on the logo should change to white. Instead the logo is always white and unaffected by the power button. The logo is flickering as it appears to struggle to have stable voltages and "boot up".
THINGS TESTED
==========
1) Followed troubleshooting section of service manual (thank you for uploading these on this site!)
2) +5VSB is working fine and does not fluctuate
3) U22 (1117 regulator) pin 2 should be regulating 5VSB down to 3.3VSB. Instead when I measure pin 2 I see the voltage fluctuating between 0.7V and 1.2V.
4) I checked resistance between 3.3VSB and GND and measure 0.8 Ohms with my Fluke (probes shorted are ~0.2).
I have another main board that is also damaged (no image, but stable power supplies at least), so I tried using it for some troubleshooting. With that main board connected my TV voltages are stable, and the VIZIO logo works as expected. Here are my test results with the "better" main board:
3a) 3.3VSB is steady 3.3. This tells me the problem is on the main board and that the service manual is correct...
4a) Resistance between 3.3VSB and GND measures 15 Ohms with my Fluke
5) I changed U22 (the 3.3VSB regulator) which had no affect
6) Looked for bulging cap's and didn't see any
7) EC21 was the only electrolytic cap I could find tied to 3.3VSB
PROBLEM
======
1) When plugged in, the main board can not regulate 3.3VSB.
QUESTION
=======
What should I check for pulling down the 3.3VSB supply? Is EC21 my best bet? It's not a hard short but the resistance is low enough my meter beeps if I find ground which makes it a bear to find what IC's might be using 3.3VSB. This seemed like a straight forward problem and since I have a "working" main board I as hoping I could figure this one out but haven't been able to figure out where to go...
Many thanks in advance for any suggestions!
-Chris
======
This is a Vizio VO42L. It won't power on. When the TV is first plugged in the VIZIO logo should be orange. When the TV is turned on the logo should change to white. Instead the logo is always white and unaffected by the power button. The logo is flickering as it appears to struggle to have stable voltages and "boot up".
THINGS TESTED
==========
1) Followed troubleshooting section of service manual (thank you for uploading these on this site!)
2) +5VSB is working fine and does not fluctuate
3) U22 (1117 regulator) pin 2 should be regulating 5VSB down to 3.3VSB. Instead when I measure pin 2 I see the voltage fluctuating between 0.7V and 1.2V.
4) I checked resistance between 3.3VSB and GND and measure 0.8 Ohms with my Fluke (probes shorted are ~0.2).
I have another main board that is also damaged (no image, but stable power supplies at least), so I tried using it for some troubleshooting. With that main board connected my TV voltages are stable, and the VIZIO logo works as expected. Here are my test results with the "better" main board:
3a) 3.3VSB is steady 3.3. This tells me the problem is on the main board and that the service manual is correct...
4a) Resistance between 3.3VSB and GND measures 15 Ohms with my Fluke
5) I changed U22 (the 3.3VSB regulator) which had no affect
6) Looked for bulging cap's and didn't see any
7) EC21 was the only electrolytic cap I could find tied to 3.3VSB
PROBLEM
======
1) When plugged in, the main board can not regulate 3.3VSB.
QUESTION
=======
What should I check for pulling down the 3.3VSB supply? Is EC21 my best bet? It's not a hard short but the resistance is low enough my meter beeps if I find ground which makes it a bear to find what IC's might be using 3.3VSB. This seemed like a straight forward problem and since I have a "working" main board I as hoping I could figure this one out but haven't been able to figure out where to go...
Many thanks in advance for any suggestions!
-Chris
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