General ? concerning PS_On and other DC voltages from PS to MB

[millenial]

Okay, I recently checked out a Vizio VF550m with PSU part #: 0500-0507-0610..

The TV itself has a standby orange glow, but never powers on. At first I thought it was a mainboard issue, but when I tested voltages for everything, all the +12 V DC pins that are labeled on the legend next to the connector pins that go to the mainboard, read 0 V DC and even the PS_On read 0 V DC. So I thought to myself, oh this is definitely a power supply issue. I did get standby voltages for the power board, but again no PS_On and none of the +12 V's or any of the 24 V's.

I was confident in my diagnosis, until I read somewhere that PS_On and the other pins are SUPPOSED to read 0 V's, until it receives a power on command from the mainboard. However, this is just if there is a VS_On pin, which every power board and tv do not utilize, correct?

Any help with this would be appreciated, thanks!

[budm]

Re: General ? concerning PS_On and other DC voltages from PS to MB

PS_ON is generated by the Main board which is running form the 5VSTBY power supply, so right now the main board is not sending the PS_ON signal.
Common problem in Vizio main board is bad Voltage regulator ICs.
Read the basic TV troubleshooting guide.

[Nick's Tvs]

Re: General ? concerning PS_On and other DC voltages from PS to MB

Lets revive this bad boy!

I have a VF550m with Power supply 0500-0507-0610 and main board 3655-0022-0150

I have the same symptoms as OP aside from the PS-ON, when pressing the power button, I get 1.2 volts and pressing it again makes it go down to 0v. So the main board is sending the turn on signal to the power supply, its just not turning on. (Also I just discovered this this morning after trying to fix the main)
I went ahead and got a repair kit from zemtronix assuming this was a bad main due to the high failure rate on these.
http://www.ebay.com/itm/VIZIO-Main-B...QAAOSwv0tU~1pr

The repair kit included 5 voltage regulators and the EEPROM.
Obviously I am on this thread so that repair did not make a difference.

I then checked out the power supply repair kit from shopjimmy
http://www.shopjimmy.com/vizio-0500-...repair-kit.htm
I have not purchased it and won't but I used it to see exactly what commonly fails on the power supply but it seems like their repair kit is more geared towards a total failure of the PSB. I checked all the components listed anyways and all checked out ok.
One thing I am unsure of is the white ceramic thermal fuse R817 rated 5w 100KJ is not measuring like a fuse. I think it was about 6Mohm. Does this mean it is out or is it due to its extremely high KJ rating?

Picture attached of the component I am talking about.

[Nick's Tvs]

Re: General ? concerning PS_On and other DC voltages from PS to MB

For some reason the other computer I was using was not allowing the picture to load so here it is.

[budm]

Re: General ? concerning PS_On and other DC voltages from PS to MB

With 1.2VDc for Pson, what dcv do you get between the two legs of the main filter cap? The Pson Voltage just needs to be high enough to bias ob the B-E junction of the transistor that turns on the OPTO.

[Nick's Tvs]

Re: General ? concerning PS_On and other DC voltages from PS to MB

Budm,
Thanks for assisting and sorry for the delay, just got super busy at the shop last couple of days.
I get 106 VDC on positive and 58 on negative side of that main filter cap.

[budm]

Re: General ? concerning PS_On and other DC voltages from PS to MB

Budm,
Thanks for assisting and sorry for the delay, just got super busy at the shop last couple of days.
I get 106 VDC on positive and 58 on negative side of that main filter cap.

It sounds like you use the chassis as the GND ref for your meter, you are working in the DC primary side so you have to use the Negative leg of the main filter cap as the GND ref for the meter.
It looks like when you measure it between the two legs you will see around 160VDC at this point.

[Nick's Tvs]

Re: General ? concerning PS_On and other DC voltages from PS to MB

Oh darn, yup that is correct.
I honestly don't know how to measure this component. The way the heat sink covers it makes it fairly impossible to get 2 leads down there at the same time, and I am looking at a descent amount of solder work if I want to get that heat sink out and I do believe there might be voltages going through it, so if I take it out it might affect the way the board behaves.

[budm]

Re: General ? concerning PS_On and other DC voltages from PS to MB

You can solder two long wires on the bottom side of the board so they can go to the meter.
Other thing that you can do also is to remove the PS-ON wire feeding the power supply board and then use 1K resistor between PS-ON pin and STBY pin of the power supply board to see if you will get 12V and the 24V back.

[Nick's Tvs]

Re: General ? concerning PS_On and other DC voltages from PS to MB

Budm, very smart you are.

168VDC is my reading.

[budm]

Re: General ? concerning PS_On and other DC voltages from PS to MB

So at this point it is either 1.2V is too low to turn on the power supply and the PFC Voltage booster or there is problem with Transistor that is receiving the PS-ON but still does not turn on. If it does turn on using the resistor to force on then we will need to look at the main board to see why it is only allow the signal to go up to only 1.2V.

[Nick's Tvs]

Re: General ? concerning PS_On and other DC voltages from PS to MB

Shorted 5v to PS-ON and I got the 24 volts and 12 volts to show up. I guess we are in the clear on the PSB working properly here.
I am pretty good with component level trouble shooting on any board except mains, logics, and t-cons. I don't usually trouble shoot main boards very often so I will need some guidance on this one. I usually run to the repair kits and EEPROMS which I already have done.
Main board part# 3655-0022-0150
Link to picture:
http://assets.shopjimmy.com/media/ca...0150-TOP_2.jpg

[budm]

Re: General ? concerning PS_On and other DC voltages from PS to MB

What you can do is to have all the connectors back in place except the Pson wire, leave the force on resistor in place (I do not like to short the 5V directly to any command pin in case there is shorted circuit that may damage the Stby power supply). If all other function of the main board are OK then you should have full function of the TV, if not then you have more than just bad Pson, it may be due to bad regulator IC on the main board.

[Nick's Tvs]

Re: General ? concerning PS_On and other DC voltages from PS to MB

Will give that a try tomorrow when I get back to the shop.

[Nick's Tvs]

Re: General ? concerning PS_On and other DC voltages from PS to MB

Ok sorry about the delay, I got caught up with other repairs and forgot about this set.

Yup so the tv turned on, backlight came on and the tv is operational with the main board plugged in and the turn on command shorted to 5 volts.
Where do we go from here?

[budm]

Re: General ? concerning PS_On and other DC voltages from PS to MB

Next step will be tracing out the connection on the PS-ON pin on the main board side, there is switched Transistor on the main board that controls the PS-ON signal, it may be leaking and not allowing the PS-ON to go high enough.
See example circuit on how it is done.

[Nick's Tvs]

Re: General ? concerning PS_On and other DC voltages from PS to MB

Ok I have tried to follow the path, but am clueless at this point.
I checked some of the transistors and took one out of circuit to measure it, but I got nothing.
Attached are a few pictures. if you could guide me just a little more here.
Thank you

[budm]

Re: General ? concerning PS_On and other DC voltages from PS to MB

I cannot trace the connection from the pictures but what you can do is to test the DCV between GND and the Collector (middle pin) pins of transistor Q1, Q2, Q5, Q7 when TV is off and when TV is on to see if you can see the DCV at the Collector change state and how much changes.
https://www.badcaps.net/forum/attach...5&d=1455308553
BTW, which pin on that white connector is the PS-ON pin?

[Nick's Tvs]

Re: General ? concerning PS_On and other DC voltages from PS to MB

Pin 1 top pin

[budm]

Re: General ? concerning PS_On and other DC voltages from PS to MB

Take DCV reading on R11 (buffer resistor case pin 1 is accidentally got shorted to GND) right pin, it should be higher than 1.2V (on the left pin of the resistor which is connected to pin 1 connector).
I also expect the right pin of the resistor to be connected to the Collector of one of those 4 transistors through another resistor, It looks to me Q1, Q2 are for the PS-ON circuit.