Vizio M421VT no power

[dbier63]

When set is plugged in all that I get is the logo light. No relay action or any back light at all. took voltage measurements from CN904. Only voltage present was the 5.2V all others were zero. Also no voltage present on any of the VLED terminals. Please advise.
Thanks

[budm]

Re: Vizio M421VT no power

Please upload the pictures of the whole back side of the TV so we can see how all the boards are connected together.
Since you do have the standby Voltage to run the main board but there is no command signals coming out of the main board to turn on the rest of the power supplies then there is problem in the main board some where.

Which one of these is your main board?
http://www.shopjimmy.com/catalogsear...q=Vizio+M421VT

[dbier63]

Re: Vizio M421VT no power

Thanks Bud, here are the pictures

[CapLeaker]

Re: Vizio M421VT no power

Picture #2 top left, there is a pin out. We need that too.
Try to turn that TV on and post all the voltages you get from that connector with the corresponding pin out.

[dbier63]

Re: Vizio M421VT no power

Ok I did that earlier and the only ones that had any voltage were the 2 five volt pins and they were both close to 5. I will check all again tonight and write them down. I assume that you want the readings with the connector on?

[budm]

Re: Vizio M421VT no power

There are pin labels for that CN904 of the power supply/LED driver board but the wires are in the way so I cannot see the labels for the pins.
https://www.badcaps.net/forum/attach...7&d=1443656955

[dbier63]

Re: Vizio M421VT no power

Board pictures

[budm]

Re: Vizio M421VT no power

OK, so far we know that the main board is getting the 5VSTBY to run, but looking at the power supply board connector CN904, there is a pin named 'ACD' for AC Detect which will generate the signal to tell the main board the condition of the incoming AC'
You have indicated that you only has the 5V and nothing else on other pins of the CN904.
I do not know if the ACD signal should be normally HIGH if the AC is OK, or normally LOW if AC is not OK. This ACD signal can lock up the main board and not allow it to send any command signals until the AC is OK.
So it can be that we are having the problem with ACD or the ACD is OK but there is the problem with the main board.
In SONY TV ACD normal = HIGH, I do not know what VIZIO uses.
One way to find out is to remove that ACD wire from the CN904 and then use 1K , 1/4W resistor between the 5VSTBY and the exposed end of that ACD wire to pull the ACD signal to HIGH to see if the TV will turn on.

[dbier63]

Re: Vizio M421VT no power

Great I will get a 1K 1/4 watt resistor tonight from work and give it a try tomorrow. Also record all voltages and post the numbers.

Thank you for your input.

[dbier63]

Re: Vizio M421VT no power

Removed terminal connector from ACD and installed 1k 1/4w resistor in series with 5.2v terminal. No change. Still no power. Took voltage readings from the following points on CN904:
ON-OFF) .366v
DIM) .002v
12v) .377v
12v) .377v
GND) -.003v
GND) -.003v
GND) -.003v
24v) -.005v
24v) -.005v
PS_ON) -.002v
5.2v) 5.156v
5.2v) 5.156v
ACD) .001v

[budm]

Re: Vizio M421VT no power

You have to have the connector back in place for the main board to communicate with the power supply but without the ACD wire in place.
But If you do have the connector in place then the main board dead.

[dbier63]

Re: Vizio M421VT no power

All readings are with reference to GND.

[dbier63]

Re: Vizio M421VT no power

I did have the connector in place. Just removed the ACD pin from it.

[dbier63]

Re: Vizio M421VT no power

Thanks Bud, it does look like a bad main. I checked around not a cheap board.
Figures. Thanks again

[budm]

Re: Vizio M421VT no power

So the free ACD WIRE that goes back to the main has a resistor connected to the wire and another end of the resistor is connected to 5V and all the signals are all dead, then the main board is really bad then.

[dbier63]

Re: Vizio M421VT no power

What I would really like to do is find out which board component is bad then take it to work and replace the part. Need a schematic.

[budm]

Re: Vizio M421VT no power

You can try disconnecting the WIFI board and see what happen, then try the cable to the key board (but you will have to use the remote to tuRn on the TV).
There should be some Voltage regulator ICs on the main board, and some fuses too.

[dbier63]

Re: Vizio M421VT no power

Yes correct I installed a resistor from the 5.2v terminal connector which was plugged into the PS board. The other end of the resistor had the ACD free wire clipped to it.

[dbier63]

Re: Vizio M421VT no power

Ok I'll try wifi board disconnect and check results.

[dbier63]

Re: Vizio M421VT no power

No change with wifi disconnected