Vizio P50HDM no display or sound

[Cooter]

Hi everyone, new guy here.

Just picked up a Vizio P50HDM with seller's assurance that "it needs a power supply." Having successfully repaired my 32" Vizio plasma (don't remember the model number), I thought, "How hard can it be?"

Well, of course I'm stuck. Didn't see any blown caps like my other TV had, but did find the 250V 4A FS3 on the ysus board had blown. I replaced the fuse with no improvement - other than it now has the same 190V or so DC on both sides of the fuse.

When I plug it in, the amber LED illuminates, and I hear some clicking - relays, I assume. Pressing the power button changes the amber LED to green, and I hear more clicking. Maybe 10 seconds after pressing the power button, I hear a slight "thud" noise from the speakers. Looking inside, various LED's illuminate on the main board and Tcon board. I hear a hum from the ysus and zsus boards as well as the power supply. Turning it off causes the LED to go back to amber, then flash green 10 times. For what it's worth, I'm not connected to a source at this time, but I figured it would at least show "No Signal" or a menu or something.

I've checked for voltage on many of the cables that are labeled on the boards, and they have "some" voltage - not sure exactly what some of them should have, but for example, all of the 5V signals I checked have between 4.9 and 5.1V.

I'm pretty new to the TV repair thing, but I'm confident working with small delicate stuff and high voltage, and I can generally even follow instructions! Any help you could provide would be appreciated. Thanks.

Greg

[tom66]

Re: Vizio P50HDM no display or sound

Turn the lights out in the room. Does the screen glow at all (may be very slight) with power on?

[Cooter]

Re: Vizio P50HDM no display or sound

Doesn't look like it lights up at all.

I mentioned that LED's light up on the main board and the Tcon board. The PDF manual I found online doesn't call it the Tcon board, doesn't actually call it anything, so I hope I didn't call it by the wrong name. It's the board above the main board that has a couple LED's that light up when I turn it on.

I can bring home an oscilloscope tomorrow if needed to test something.

Thanks again.

[tom66]

Re: Vizio P50HDM no display or sound

T-con board (LCD) == Control/logic board (plasma)
Scope with 10X probe can help rule out sustain boards.

[Cooter]

Re: Vizio P50HDM no display or sound

I can check that tomorrow night. If you can tell me what I should check.

What board(s) and pins? I have some sample traces, so I may be able to compare them, but they're not all labeled in a way that's understandable to me.

[tom66]

Re: Vizio P50HDM no display or sound

Pictures and I'll highlight test points.

[Cooter]

Re: Vizio P50HDM no display or sound

Here's an overall shot as well as some closer shots.

[tom66]

Re: Vizio P50HDM no display or sound

So, basically, left hand board (from your first pic) is the Y-Sustain, and the right hand board is the Z-Sustain.

* Plug the TV in with no boards disconnected, observe symptoms and keep careful note.

* Unplug TV. Wait approx 1 minute to allow bus voltages to discharge to nearly zero. (Safety.)

* Disconnect Y-Sustain. Plug in TV, observe symptoms and keep careful note.

* Unplug TV. Wait approx 1 minute to allow bus voltages to discharge to nearly zero. (Safety.) Re-connect Y-Sustain.

* Disconnect Z-Sustain. Plug in TV, observe symptoms and keep careful note.
boards disconnected, observe symptoms and keep careful note.

* Unplug TV. Wait approx 1 minute to allow bus voltages to discharge to nearly zero. (Safety.) Connect as normal.

[Cooter]

Re: Vizio P50HDM no display or sound

Okay, when I plug it in, the green LED on the front flashes briefly then the amber LED lights up. It then flashes green 11 times (1 long and 10 short) and ends on amber. While this is happening, an LED (D10, I think) lights up and stays lit. On the control/logic board, D15 then D17 light up in sequence accompanied by a click on the power supply and a "squeal" noise that sounds like when they charge the paddles in the emergency room before they shock someone's heart. About 3 seconds later, there is another click from the power supply and the LED's on the logic board turn off.

With Y-sus unplugged, LED sequence on front is the same as before. The LED on the main board is the same as before. Clicks from power supply are the same as before. LED's on the control/logic board do not light up. I don't know if it received power from Y-sus or power supply - looks like it gets it from the Y-sus. I had the cable and ribbon between Y-sus and the control/logic board unplugged.

With Y-sus plugged back in and Z-sus disconnected, everything behaves the same as with everything connected.

If I can jump to a conclusion, might this point back to the power supply?

[Cooter]

Re: Vizio P50HDM no display or sound

I didn't turn the TV on while performing these checks. Should I have done so?

[tom66]

Re: Vizio P50HDM no display or sound

Yes. Sorry if I did not mention this. TV needs to be turned on normally. But unplugged while removing connectors.

The squealing points to a shorted power supply output, possibly, which may be from a failed Y-Sus or Z-Sus.

Vizios do not use blink codes. Do not worry yourself over the blinks. The other LEDs indicate control board status & plasma panel temperature.

[Cooter]

Re: Vizio P50HDM no display or sound

With Ysus disconnected, when I turn it on, I let it go through previous cycle to let power supply click. Once turned on, power supply clicks, no squealing, and D10 on main board flashes a sequence too fast to determine, then flashes rapidly. When turned off, power supply clicks once and D10 on main board turns on steady, and on the control/logic board D2 lights up briefly then all the LED's on that board go out.

With Zsus disconnected and Ysus connected, same thing.

Forgot to mention on the control/logic board D1 lights up about the same time D15 lights up. It was sort of hidden under a piece of tape for a cable.

[tom66]

Re: Vizio P50HDM no display or sound

"With Zsus disconnected and Ysus connected, same thing."
Same as before with Ysus disconnected or with original symptoms?

[Cooter]

Re: Vizio P50HDM no display or sound

Sorry, with Zsus disconnected, it is the same as with Ysus disconnected.

[tom66]

Re: Vizio P50HDM no display or sound

K, so can you measure the "Vs" test point while set is running (all boards connected) and see what you get.
It will probably be around 190V for an old LG PDP panel like this.

[Cooter]

Re: Vizio P50HDM no display or sound

Vs is 192.4V at the power supply, going into ysus, and going into zsus. Va is 59.9V - seems to match the sticker I just found inside...

[tom66]

Re: Vizio P50HDM no display or sound

OK, so the PSU is working. Whining may be normal. Now, onto the fun of diagnosing the other faults. You have no picture. No glow. You have good Vs and the control board is functioning. The fault is most likely with the Y-sustain. You would need an oscilloscope to be 100% certain.

[Cooter]

Re: Vizio P50HDM no display or sound

Of course I forgot to bring home my oscilloscope from work, but I can do it tomorrow. Where do I check? I'm used to using a single channel Picoscope for automotive stuff, so I'm pretty sure I can get a good trace, just need to know what to check and what I should get.

I can take close up photos of ysus if you need them. All the stuff inside is LG, but you probably knew that.

[tom66]

Re: Vizio P50HDM no display or sound

OK, grab your scope when you can and make sure you either have a scope rated for at least 400V inputs with a switchable probe, or a fixed 10X probe. I use a fixed probe so I can't switch it to 1X accidentally and blow up my Rigol scope which is 300V rated. Sustain waveform peaks at around 350V for an LG (Vs + Vset.)

Can you get pics around the Y-sustain to Y-buffer connectors, and Z-sustain outputs. On the Y-sustain we're looking for a point marked Vscw or WAVEFORM.

[Cooter]

Re: Vizio P50HDM no display or sound

Hmmm, I bet my scope isn't rated for voltage that high, but I'll check.

Pics attached of ysus and zsus - hope they show what you're looking for.

In the automotive world where I work, I frequently deal with techs who need to diagnose something but don't have scopes, so I try to find ways to help them find out the same information or at least something useful by using a meter. So here's the question: If I use a meter, it will show average voltage, but not the waveform, although I can capture minimum and maximum voltage provided the sampling rate is fast enough. I'm pretty sure my Fluke meter is rated for 400V - is this type of failure something where I'll see an average voltage close to 300V (or whatever) if it is OK, and a failure will be 0V? Or would a failed board still show the same average voltage, but the pattern would just be incorrect? I'd like to see the patterns, but if I can determine it's dead with a meter, that's all I really need to know, and it would be point to the ysus, right?