Vizio 32" VO320E Intermittent Issues

[keeney123]

Re: Vizio 32" VO320E Intermittent Issues

To check the fuse. Unplug unit and just ohm it out while in circuit. It should be under 1 ohm. See if BudM has knowledge of where voltage is coming from to fuse or possible a schematic to trace it?

[bahowe1]

Re: Vizio 32" VO320E Intermittent Issues

On that fuse, TF1, I am getting 0.9 ohms. So, I guess it is showing that the fuse is good, but power is not getting to it. Does anyone have any knowledge of the components to check prior to TF1?
Thanks for all your help.
Ben

Now that I think about it, I did see a thread about power not coming out on pin 8 of some component. I can't really remember anymore details and can't find the post again, but wonder if that was a similar issue? Wondering if my scant few details might help ring a bell?

[budm]

Re: Vizio 32" VO320E Intermittent Issues

OK, if I traced out the board correctly I believe U21 is the switched MOSFET that supplies the Voltage to the fuse.
So use Ohm meter to check the resistance between the fuse and the out pins of the U21, it should show < 1 Ohms or so, if it does, then check the DC Voltage on the Input side of U21, should have DC Voltage on it, then take the reading of all the pins of U21 when TV is OFF and when TV is ON. I also need the P/N of that U21.
BTW, I did remember about that thread that I help out the other guy that has similar Vizio board as yours, it was about a month or two ago.
This is the thread:
https://www.badcaps.net/forum/showth...&highlight=U21
So check the inductor.

[keeney123]

Re: Vizio 32" VO320E Intermittent Issues

It also looks like F2 is a fuse on the input to U21. If nothing is coming out of U21 check F2 to see if it has continuity.

[budm]

Re: Vizio 32" VO320E Intermittent Issues

Fuse F2 left terminal is directly connected to the connector so as U21 input so it is not used for feeding Voltage the input to U21, if I remember correctly, that is the fuse for 12V which feeds the 7805 IC and the audio circuits.

[bahowe1]

Re: Vizio 32" VO320E Intermittent Issues

If this were a game of 'hot and cold', I'd say we are near fire! When I checked the resistance between the fuse F2 and U21, on the inputs I was getting '0's on the pins that I'll call one and three (the ones that budm's drawing did not show connections to) and 0.58's on the other two pins. When I checked the output pins, they rapidly were increasing in resistance. They would start around less than one and rapidly climb. Not knowing if that was right or not, I turned on the TV and the voltage on all input pins was 12.18v, same as the fuse 2 voltage, and the outputs all had 0! Similarly, all components down the line in budm's drawing had no voltage either. U21 PN is 4953_M, 932154. The underline represents a number I could not read, it looked to either be a 0,6, or 8. The 'M' was printed very close to that number. Is this our smoking gun? Also does anyone know the part number for Fuse F2?? It's a 5amp.

Also, I have been reporting that sometimes the backlights turn on and sometimes they don't, well I am starting to see consistency. The first time I plug in the TV and hit the on button, backlights will come on. Anytime after that, not the case.

[budm]

Re: Vizio 32" VO320E Intermittent Issues

"the ones that budm's drawing did not show connections to" I do not show that because you can clearly see that the input is connected directly to the left side of the use and goes to the white connector. Do not worry about the fuse, we know that the fuse is good otherwise you will not have 12V feeding the 7805 regulator.
Post 1:
U11
7805CT
RAG930G
0
0
0
12.18
0
5.02
Right now it does not have voltage at the output can be due to there is no ON command to turn on the U21, that is why I ask for voltage readings on all the pins of U21.
Post 23: then take the reading of all the pins of U21 when TV is OFF and when TV is ON

And just to be sure, what is the resistance between the output and the fuse TF1?

[keeney123]

Re: Vizio 32" VO320E Intermittent Issues

To BudM in your picture you have F2 connected directly to U21 pins 1&3 also, you have pins 5,6,7,8 connected together. That only leaves Pins 2 or 4 which I do not know if they are connected together, but one would seem to be gnd. It would help if there was a part number of U21 so we could look up the function. Perhaps it is an inverter, when input is high output is low. I do not know?

[budm]

Re: Vizio 32" VO320E Intermittent Issues

That is the dual P-CH MOSFET, so there are Gate pins on it which we need to find out if it will change state when TV is off and when TV is on, if there is no change of state, then the processor is not sending the Gate drive signal, if the Gate drive signal is present, then it can be the bad MOSFET.
It is the same MOSFET 4953 as used in the other thread I have the link to.
Input pin 1 and 3 are the Source pins, pin 5~8 are the Drain pins, pin 2 and 4 are the Gate pins.

[keeney123]

Re: Vizio 32" VO320E Intermittent Issues

So my understanding is the D to S voltage in this case is 12.18 volts and when the G to S voltage gets to 10 % of -12.18 volts the MOSFET conducts and then there is a time delay for it to trigger on fully and stays on until the G to S drops to 90% of -12.18 volts turning off the MOSFET which again has a time delay to fully trigger off which is the state this MOSFET is at present? Should there actually be a pulse train of timing signals coming out this MOSFET or is this like a one shot condition?

[bahowe1]

Re: Vizio 32" VO320E Intermittent Issues

BudM, I did check the voltage on and off, exactly as you told me to, but unfortunately I jumped to conclusions and did not respond with those values. I will check my sheet again tonight and give those values. I am pretty certain that I had zero volts on all those pins when the TV was off, but let me double check. Just to be clear, we are calling pin 'S1' in your pdf file, pin 1. Then go counterclockwise for naming the rest of them?

So to be clear, my actions are:
Check voltage at all pins for U21, off condition (I already reported on).
And take resistance between outputs of U21 and TF1.
I will report all values back, but just in case I find 0 volts on all pins in the off condition, and you already know volts in on condition, what do i check next?

Seriously guys - thanks for hanging in with me!

[budm]

Re: Vizio 32" VO320E Intermittent Issues

So my understanding is the D to S voltage in this case is 12.18 volts and when the G to S voltage gets to 10 % of -12.18 volts the MOSFET conducts and then there is a time delay for it to trigger on fully and stays on until the G to S drops to 90% of -12.18 volts turning off the MOSFET which again has a time delay to fully trigger off which is the state this MOSFET is at present? Should there actually be a pulse train of timing signals coming out this MOSFET or is this like a one shot condition?

The MOSFET is just being used as a simple switch, it is either on to provide the 12V to run the T-CON circuit or off to kill the power to the T-CON when the TV is off or in standby mode, the GATE gets steady state, in this case it is P-CH and the Source is at 12V so the Gate will have to be pulled LO toward ground, no pulsing, it is static state either HI or LO signal to turn on the MOSFET. WHen TV is powered on the processor will send out the signal to turn on the the power supply, the inverter, the T-CON.

[budm]

Re: Vizio 32" VO320E Intermittent Issues

"Not knowing if that was right or not, I turned on the TV and the voltage on all input pins was 12.18v, same as the fuse 2 voltage, and the outputs all had 0! Similarly, all components down the line in budm's drawing had no voltage either. "

Sorry it was not clear to me, I was hoping to see the report of the voltage readings in this format:
Pin1: xxxx V
Pin 2: xxxx V
..........
I can see that you are getting 12V at the input, 0V at the out put. I have no idea as to "all components down the line outputs all had 0!" means.
The GATE voltage is the one I am looking for at this point, so report the reading on the GATE pins when TV is OFF and when TV is on.

[budm]

Re: Vizio 32" VO320E Intermittent Issues

BTW, you can jump the input to the output after the TV is ON just to see if the TV will function properly beside the problem with this section of the circuit.

[bahowe1]

Re: Vizio 32" VO320E Intermittent Issues

Great news... followed by bad news.

So I ohmed out output U21 to TF1
0.1.
Voltage on all pins 1-8 when OFF
0
Voltage when ON
1 = 12.2
2=12.18
3=12.2
4=12.18
5-8=0
So I jumped it, and viola - PICTURE!!!! Blue screen with the 'No Signal' hopping around. I did my Happy Dance and then thought, 'well, I need to see if I can get it to work by turning the switch off and on'. Jumped it again, and it all shut down. I have no idea what happened, but no backlights, no nothing.
The power board fuse is still good. Fuse F1 and F2 still seem to be good (F2 I keep asking about because I currently have that jumped to another external fuse because that one blew a long time ago). Vizio light now stays Orange. Will not turn white. I have 5v on the power supply, but I have no 12 volts any longer at the power supply.
Thank you guys so much. I wish I could report that I was ready to change U21 and F2 and be done, but it looks like I am back at square one.
Also, one more question, should I have heard static or anything when I had 'No Signal'? Volume was up, so I still don't know if something was wrong here or not but couldn't hear anything.

[budm]

Re: Vizio 32" VO320E Intermittent Issues

Well, from the voltage readings, the MOSFET is not being turned on, the Gate Voltage has to be at least 2~3V lower than the Source pin.
I do not know what happen as to why you now have new problem. You did not accidentally connect the jumper to the Gate pins?

[keeney123]

Re: Vizio 32" VO320E Intermittent Issues

Also, did you ohm out TF1 after you stop getting 12 volts from you power supply?

[bahowe1]

Re: Vizio 32" VO320E Intermittent Issues

I'm pretty positive that I did not jumper to the gate pins. I had actually jumped the MOSFET a couple times because I was so excited to see the screen that I then wanted to check sound. Getting no sound, I thought I need to see if it will power on and off. It was on, I jumped it and I just heard stuff sort of shut down.

So, I need F2 and the MOSFET. Should I order those now? If so, are you guys using Digikey? I can't seem to find the parts on there.

Kenney123 - I did not ohm out TF1 after the shutdown, because if I understand it right, it's not even getting power to it since I have no 12 volts at the power supply and none at F2.

I really appreciate all the help you guys have provided. I really want to get this thing fixed now - I really don't want it to beat me. But, I'm sort of lost in where to start back?

[budm]

Re: Vizio 32" VO320E Intermittent Issues

F2 is not used for feeding the Voltage to the U21, it is used for feeding the 12V to the 5V 7805 regulator and power amplifiers circuit.
"because if I understand it right, it's not even getting power to it since I have no 12 volts at the power supply and none at F2." and that is because the main board is no longer sends the PS_ON to turn on the 12V power supply, and you can tell because the Vizio logo did not turn white.

[keeney123]

Re: Vizio 32" VO320E Intermittent Issues

The reason I ask about the TF1 ohm out after the shut down is that after you jumper-ed the 12 volts input to the output of U21 you could have had a component on the output side that shorted out which took out your 12 volt supply there fore the TF1 fuse would be blown.