Vizio SV420M, Power light stuck on. No standby or picture

[SmartSped]

Hello all. I have a Vizio SV420M that's giving me strange symptoms. When I plug it in, the power light immediately turns on, completely bypassing standby. There is no picture or backlight and it doesn't seem to react to any of the buttons. The only way I can get the white light to turn off is by unplugging it. I'm not really sure where to start on troubleshooting this thing since the problem seems odd. Any help would be appreciated. I've attached photos of the boards.

[SmartSped]

Re: Vizio SV420M, Power light stuck on. No standby or picture

Couple more photos of the main board.

[tom66]

Re: Vizio SV420M, Power light stuck on. No standby or picture

Is the logo light white or orange?

[SmartSped]

Re: Vizio SV420M, Power light stuck on. No standby or picture

It's white. It's not in standby at all.

[SmartSped]

Re: Vizio SV420M, Power light stuck on. No standby or picture

Does anyone have an idea on at least which board might be the problem?

[budm]

Re: Vizio SV420M, Power light stuck on. No standby or picture

https://www.badcaps.net/forum/attach...7&d=1413657824
What DC voltages do you have on those pins? At this point I expect the main board.
Shopjimmy sells EEPROM so that can be a suspect.
http://www.shopjimmy.com/catalogsear...izio+SV420M%2C

[SmartSped]

Re: Vizio SV420M, Power light stuck on. No standby or picture

The 5volt is supplying 5 volts but I have nothing on the 12v lines. But I'm guessing that's normal right?

[budm]

Re: Vizio SV420M, Power light stuck on. No standby or picture

The 12VDC will not be present until the main board sends out the PS_ON (>2.5VDC, when power switch is activated) signal to turn on the 12V power supply, and the PFC Voltage booster circuit to supply the voltage to run the inverter circuit.
The 12V is supplied through the switched MOSFET Q910.
http://www.shopjimmy.com/media/catal...810-bottom.jpg

If the PS_ON is present, then you should also see>350VDC on the two legs of the main filter cap if the PFC is working.

[ecking767]

Re: Vizio SV420M, Power light stuck on. No standby or picture

The 5volt is supplying 5 volts but I have nothing on the 12v lines. But I'm guessing that's normal right?

yes that normal +12v is for audio. do you have any other voltages coming from the power supply with main board power cable connected ? DIM, INV_ON, STATUS,

[budm]

Re: Vizio SV420M, Power light stuck on. No standby or picture

" I have nothing on the 12v lines. But I'm guessing that's normal right?"

[SmartSped]

Re: Vizio SV420M, Power light stuck on. No standby or picture

I haven't tried forcing PS_ON yet. I'm looking for a resistor. I'll let you guys know my findings afterwards.

But do you think with the power light already being on by default that I would even need to force PS_On in the first place?

[ecking767]

Re: Vizio SV420M, Power light stuck on. No standby or picture

I haven't tried forcing PS_ON yet. I'm looking for a resistor. I'll let you guys know my findings afterwards.

But do you think with the power light already being on by default that I would even need to force PS_On in the first place?

no dont force the power supply on, I'm trying to understand what the main board cpu is doing. this could be eeprom related, that where I will start.

[SmartSped]

Re: Vizio SV420M, Power light stuck on. No standby or picture

I'll test the DIM, INV_ON, and STATUS pins for voltage in just a bit and reply back.

[SmartSped]

Re: Vizio SV420M, Power light stuck on. No standby or picture

I disconnected each of these wires separately and I received no voltage on any of those three lines.

The voltages on these lines is tested from the main board side, correct?

[ecking767]

Re: Vizio SV420M, Power light stuck on. No standby or picture

I didn't want you to disconnect the main board power cable. you was suppose to take those measurement with the main board connected to the power supply. take those measurement from the main board side.


Also can you check the main board CPU temperature by placing your hand on the heat-sink with the power cord plug in?

[SmartSped]

Re: Vizio SV420M, Power light stuck on. No standby or picture

I took voltage reading with everything connected. Still no voltage on those 3 lines. CPU heat sink is fairly warm.

[budm]

Re: Vizio SV420M, Power light stuck on. No standby or picture

Well what do you get on the PS_ON pin? More likely the main board problem.

[ecking767]

Re: Vizio SV420M, Power light stuck on. No standby or picture

If you have soldering tools, replace the eeprom chip or replace the whole main board.

[SmartSped]

Re: Vizio SV420M, Power light stuck on. No standby or picture

I tested the PS_ON which I'm guessing is the one labeled ON/OFF in this case. I get a couple of volts from it.

[budm]

Re: Vizio SV420M, Power light stuck on. No standby or picture

OK, so the PS_ON is there which make sense since the VIZIO LOGO does turns white but you have no control to turn the TV off, you also do not have INV_ON signal either, so I would say you have main board problem.
Another problem is that you do not have 12V either even though the PS_ON is present.