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Dan, Master Tech and Repair Facility Trainer
Category: TV
Satisfied Customers: 7203
Experience:  USAF trained; A.A.S Electronics; A.A.S. Education; Currently teaching advanced troubleshooting and repair for the DoD.
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Samsung 58c550.Unbelievable.Just stopped working.No picture.

This answer was rated:

Samsung 58c550.
Just stopped working.
No picture. Has sound.
Went through a similar sudden death with Sony Bravia before this one.
Please....not again!!
Welcome back! I remember the Sony.

OK, so you have sound... can you get a MENU? Use the original Samsung remote.

Customer: replied 4 years ago.

Have original remote...but no pic.

Hit the MENU button...nada.

The red LED flickers indicating it got a command from remote...but nuttin on the screen.

Ok, let's narrow this down. Turn the TV off, and make the room as dark as possible. Get a good idea for how pitch black the screen is. Now turn the TV on and watch the screen. I know it’s still black, but did the screen seem to lighten up, even slightly?
Customer: replied 4 years ago.

k. will get back shortly

No problem.
Customer: replied 4 years ago.

No sign of life at all.

Completely dark. Waited till sound from channel came I know the cable box is transmitting and TV actually receiving the Channel data. Won't/can't show video.

OK, a few possibilities here...

* Plasma panel (least probable)
* Power supply (also unlikely, but possible)
* Scan drive board (most probable)

Wanting to do some troubleshooting? Still have that meter handy?

Is the TV under warranty?

Customer: replied 4 years ago.

TV is 3 yrs old i think.

Let me check.

Gotta get mentally prepared for deeper troubleshooting.

I'm not stable right now.


Customer: replied 4 years ago.

Bruins in Stanley Cup Final game 6 tomorrow night!

OK, how about this... I'll post the first check I would run, and you can get back to me at your earliest convenience... whenever you're ready.

Here's what I'd do, to start...

Ok, follow along...

- Disconnect the power cord
- Lay the TV face down on a sturdy table that has been lined with a blanket
- Remove the entire rear panel assembly (lots of screws... keep track)
- Standing behind the TV, find the scan drive and the sustain board (they are on the left and right hand sides, respectively… large boards with heatsinks attached)
- Connect the power cord and turn the TV on and let it sit for 30 minutes
- Touch the heatsinks, using only one hand
- Are any of them still at room temperature, or cooler? If so, which ones?


Customer: replied 4 years ago.



Plazma layin nice and flat.

Got the back panel off.

Lookin a lot easier to work on than the DLP Sony.

Been runnin for 30 minutes.....nuttin hot at all.

Looked around for fried Caps. No signs.


On the power supply board, find the wires/test points for Vs and Va. Ground your meter to any exposed chassis metal and turn the TV on... test with your red lead on the Vs and Va lines and tell me what you get.
Customer: replied 4 years ago.
Ok. Grabbin a quick icecream cone. Back to u in 35min. Thx
No problem.
Customer: replied 4 years ago.

OK. 10.2V on VS. VA is zero. Ouch!

Yep, that's no good.

OK, standing behind the TV there's a large circuit board on your left hand side. It has some heat sinks on it. I need you to disconnect that board from the power supply board. Then re-measure for Vs and Va, and let me know if they're any different.

Customer: replied 4 years ago.

With cable disconnected: VS=8.6v VA still zero

Customer: replied 4 years ago.

No Cable: VS= 8.6V VA =zero


With cable back in: VS=10.2V VA=zero

And you're measuring DC volts? Digital or analog meter?
Customer: replied 4 years ago.

DC Volts.

Digital meter (still make analog?).

I am 100% certain of these measurements.

Chasis to the corresponding TP's.

Haha... yes, they still make some analog meters. The military still uses them pretty extensively, too. The old Simpson 260 series are still excellent!

Look at the cable in between the main board (input / output connectors) and the power supply. See if there's a VS_ON or PS_ON wire... measure that during power up and see if you get a few DC volts. It might be coming from a smaller logic board if you have one of those in there. Sorry I don't have my manuals in front of me.

Customer: replied 4 years ago.

On the left we have a large circuit board(PCBA).

Is this what you refer to as the main board?

Between that board and the power supply in the middle there's nothing....just a connector bringing VA and VS over....same cable I disconnected.


Can you get me a picture of the back of the TV, that shows all the boards at once? I'll circle the boards for you.
Customer: replied 4 years ago.

No file attachment option here. Only insert.

After insert Reply failed.

Have an email I can send it to?

Try uploading it to just be sure to give me a link to the picture. It's free, and pretty easy I think.
Customer: replied 4 years ago.

Not much easier.

OK, main board outlined in red... logic board outlined in blue:

Check for a line from one of those boards, going into the power supply... PS_ON, VS_ON, something like that.

Customer: replied 4 years ago.

VS_ON does pop to 3.2V for a very short time then back to zero during power up.

PS_ON does not change from zero.

Customer: replied 4 years ago.


Not sure if you got my last response.


"VS_ON does pop to 3.2V for a very short time then back to zero during power up.

PS_ON does not change from zero."

Where do we go from here?

Hi, and sorry for the delay!

OK if you're getting 3V from VS_ON but you're only getting 8-10V on VS (even with the sustain boards disconnected) then I would suspect and replace the power supply board. Sometimes we see the sustain board short and load the power board like you're seeing, but we eliminated that possibility. All that's left in this case is the power supply.

Make sure you get the part number from the board itself, before you order a new one. Here are some good suppliers:

Sorry for the bad news, but I hope that answers your question. If it doesn't, just let me know. Oh, and be sure to rate the service before you log off tonight. Thanks!


Customer: replied 4 years ago.

A few questions:

What should VS and VA be?

What functions do VS and VA support?

Want to be sure the symptoms of no Screen but lots of other electronics working just fine(ie: channels change and we get audio) are consistant with these voltages being out of whack.


Also, VS-ON only measured 3.2V for a very brief moment. Is it a control signal or power supply?


Good questions.

Vs and Va should match the sticker inside the TV. Normally Vs is around 200V and Va closer to 60V. Depends on your particular TV but those are ballpark.

Vs is your sustain voltage... it keeps the display lit. Va is address voltage... it gets things going aka helps prime the plasma panel.

Vs and Va go from the power supply into the YSUS and the Y-BUFFERS. If they're not there, the YSUSTAIN can't do its job of priming and sustaining the plasma panel. So you'd normally have audio but zero video... no menu, no light on the screen, nada.

VS_ON is a control signal that tells the power supply to generate VS. The power supply isn't listening.

Customer: replied 4 years ago.
Allright Dan.
You clearly know what's going on.
Vs and Va voltages directly support primary video functionality.
AND they are not even close to what they need to be AND they are not likely being loaded down by faulty drive electronics.
So,clealry my Sony problem was premature power brd failuer.
Now, very likely my 2 yr old Samsung issue is also premature power brd failure. What r the odds? Thinkin of goin back to my Zenith 19" full analog.
Any way to isolate to component level on the power brd?
Probably 50-70% of the problems I see are power supply related. So the odds of your Sony and Samsung having the same issue are pretty good, actually. Sony and Samsung actually use each other's parts, too. Depends on what's cheapest at the moment.

As for component level... sure, you can. You'd need a schematic and some patience, but it's definitely doable if you have some basic power supply knowledge... isolation transformer > rectifier > filter > regulator, etc. and how they interact. Alternatively, if you just know how to test each type of component on board you can literally go piece-by-piece until you find something odd. That'll take a lot longer but you don't need to be an engineer to do it, either.

Customer: replied 4 years ago.

Well. I might be qualified.

Can you tell me where to get a schematic...and PCBA drawing?

Sure, >>click here<<.

Customer: replied 4 years ago.

Know how to get a schematic and PCBA drawing?

Sorry for the delay, Mike. Were you able to click the link I posted earlier? Here it is again, just in case:

That's the link to get a hold of the service data on this TV, including wiring diagrams, etc.

Customer: replied 4 years ago.
Ordered power supply brd from shop jimmy. Should have mid week.
Like to keep the thread open 'till I get it installed and fired up.

Little known fact about this website: From the customer's side, the thread actually never closes. You can return and post something 2 years later to this thread.

Let me know the results! Best of luck!

Dan and other TV Specialists are ready to help you
Thanks again for asking your question. If you need anything else, be sure to let me know! There are other categories, too... Legal, Medical, etc.

Oh! The site should be sending you a short survey. Good marks on the survey are definitely appreciated! Thanks in advance!

Customer: replied 4 years ago.


New PS board came in yesterday.

Looked perfect.

Installed but sadly nothing changed.




Were the scan drive and sustain boards disconnected from the power supply when you measured?
Customer: replied 4 years ago.

No. But we ran that test before though

Right. Let's run it again. Disconnect the YSUS and ZSUS, and measure VS and VA. Make sure the meter is grounded and that it's set to DC volts. You might want to put your leads in place and watch the meter display as you press the TV's power button.

Customer: replied 4 years ago.

Ok. This needs clarification.

If you recall previously, the signal names you gave do not match up with what's on the boards.

Closest I can find is PS_ON and VS_ON.

PS_ON goes to 2 cables.

VS_ON goes to 1 cable.


So, first test, loading test: power up normally then disconnect what cables? All of them?



Second test: measure PS_ON or VS_ON while TV is powered up?










To be clear...

Earlier in the thread, I asked you to measure VS and VA. You said "10.2V on VS. VA is zero."

Shortly after, and since you weren't getting adequate voltages, I asked you to find VS_ON and/or PS_ON (very different from VS and VA) to see what those values were when the TV was powered on. You said "VS_ON does pop to 3.2V for a very short time then back to zero during power up. PS_ON does not change from zero."

So if I'm going on what you've told me... you did find VS and VA, as well as VS_ON and PS_ON.

Is that not the case?

We need to be measuring VS first. If that's low, measure VS_ON during power up. I've outlined a connector in green (below) where you'll find VS:
Customer: replied 4 years ago.

I think most of the confusion is from your 2nd to last response where you asked me to "disconnect YSUS and ZSUS".

I have definitely found VS and VA...for sure.

But YSUS and ZSUS???

1) I am looking for clarification that these correspond to PS_ON and VS_ON.

2) When you said to "disconnect" them it also presented some confusion.

So back to my questions.

After normal power up I know VS=10.6V and VA=0.

At this point do you want me to disconnect ALL the cables to see if the loading problem is on another board? Or what specific cable would you like me to disconnect?

>>I think most of the confusion is from your 2nd to last response where you asked me to "disconnect YSUS and ZSUS".<<

YSUS and ZSUS are circuit boards, not voltages. Maybe that's where the confusion is. Standing behind the TV, the YSUS (y-sustain) is the large board on the left hand side of the TV. It's on the other end of the connector I outlined in green, above.


The ZSUS is on the right hand side. It looks the same as the YSUS but is about half the size.

>>When you said to "disconnect" them it also presented some confusion.<<

Knowing the YSUS and ZSUS are circuit boards, should clear this up. More specifically, to disconnect the YSUS from the power supply, you would disconnect the connector outlined in green, above.

>>I am looking for clarification that these correspond to PS_ON and VS_ON.<<

These are small voltages sent from the logic or main board, to the power supply. They'd be present during the power on sequence only, and would disappear shortly thereafter. These voltages tell the power supply to create its non-standby voltages (e.g., VS and VA).

>>After normal power up I know VS=10.6V and VA=0. At this point do you want me to disconnect ALL the cables to see if the loading problem is on another board? Or what specific cable would you like me to disconnect?<<

10.6 and 0 are definitely abnormal. Those voltages should match the label inside the TV (should be about 200V for VS and 60-80V for VA but you should check).

To see if another board is loading down the power supply, I would disconnect the YSUS and ZSUS boards from the power supply to see if those voltages come up.

Customer: replied 4 years ago.

OK. That helped.



I think VS and VA collapse shortly after coming up.

If, after normal power up, I disconnect ZSUS and then reconnect it, shortly after reconnecting it, I measure voltages up to 200V but then it is quickly dropping and eventually settles back to that 10V range.

I have never measured anything but zero for VA, yet right after reconnecting ZSUS it actually measured over 10V and also was slowly decaying.


NOTE: with ZSUS disconnected, voltages don't come back. It's only after reconnecting it that I see large voltages that decay.

To be clear...

VS and VA collapse shorly after power up, with the YSUS and ZSUS disconnected from the power supply?
Customer: replied 4 years ago.

This is excatly what I did when I reported my last results.

I powered the TV.

Didn't move particularly fast to make the voltage measurements.

Noticed that VS was around 19V and slowly decaying and eventually settled down to around 10V. VA was zero.

I then disconnected YSUS and ZSUS: Voltages didn't change.

Reconnected YSUS: no change.

Reconnected ZSUS: VS large and decaying until eventually got back to around 10V.

Disconnect ZSUS ONLY: no change

Reconnect ZSUS: 200V and decaying quickly







If you had abnormal VS and VA with both SUS boards disconnected, the problem has to be somewhere in the central boards.... power supply (already replaced), main board (A/V board with the input connections on it), or the logic board (small green board in the middle).

So you're left with the logic and the main. Tough call there, but I will tell you the logic board fails more often on this model than the main board does.