Samsung Plasma PN50C550G1F : no image, but sound is ok

[superbigjay]

Hello,

I've got my 50in plasma that just gave up on me : no image, but sound is working.

From what i have read, the cause is usually one of these three boards:

- power supply
- y sustain
- y buffer

I have done a visual check for blows caps and couldn't find any defective caps.
I have check th AC fuse and it is fine.

The 110VAC line is fine.
The Va and Vs lines behave strangely:

Right after power on, the DV voltage is near their nominal DC voltage (about 200VDC and 50VDC, but decrease until they reach 0V in about 20 seconds).

(This is with all boards connected).

Anyone have seen such behavior and could help troubleshoot the problematic board ...

I don't mind replacing 1 board if it has a good chance of fixing the problem, but I don't want to end up replacing 3+ boards and spending almost 50% of the tv price tryinng to fixing it.

Any ideas/tests/measurement that could help identify the culprit.

Jay

[sordids999]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

https://www.badcaps.net/forum/showthread.php?t=18542

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

https://www.badcaps.net/forum/showthread.php?t=18542

thanks sordids999,
that thread mention taht the most probable cause is the y-sustain.
But since the Vs voltage wasn't stable at its 200+VDC, I am not sure if it is the y-sustain, or the power supply.

It also says that the no picture is a bit more complicated to troubleshoot and suggest to create a new thread for it (post #4).

I have not read in other post a similiar problem (VS startting at about 200VDC, but decreasing rapidly).

Anyways, I'll conitnue reading the proposed thread... I'm at page 3 of 19.

Jay

[MagicSmoke]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

Need pics of PSU. Most newer Samsungs have protection circuits to shut down VA & VS when there is a fault on X ,Y or PSU.

You can disconnect the cables that power the X & Y boards and force PSU on with a 1k ohm resistor to see if VA & VS volts are present and stable.

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

I'll test the voltage with a 1K Ohm load on it.
Can I use any 1K resistor (I have a bunch of small resistors here, but not sure if I need "bigger ones" that support at least X watts)?

Here's a pic of the power supply (BN44-00330A).

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

To disconnect the X and Y boards, I only have to disconnect the power cable from the PSU to the Y-sustain board?

There no power cable that seems to go from PSU to X-board...

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

The X board seems to receive its power from a cable connected to the Y-sustain board...

[Michale32086]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

I have gone thru a whole slew of checks on a similar TV...

https://www.badcaps.net/forum/showthread.php?t=42835

Some of the checks might help you...

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

I have gone thru a whole slew of checks on a similar TV...

https://www.badcaps.net/forum/showthread.php?t=42835

Some of the checks might help you...

Thanks, will read the thread as soon as I am done drinking my coffee

Jay

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

You can disconnect the cables that power the X & Y boards and force PSU on with a 1k ohm resistor to see if VA & VS volts are present and stable.

I've done the check with a 2K Ohms load (the 1K I have are only rated at 1/4W).

When all boards connected:
or
When I disconnect only X-board
or
When I disconnect both X-board and Y-sustain

I get the same behavior:
- Vs starts at 200+ VDC and go dow to 0V in a few seconds

When I disconnect only the logic board:
- Vs starts at 0VDC and ramp up to 10VDC

When I disconnect the main board (the ones with RCA and HDMI connectors), I can't power on the TV.


Note: X board is powered from Y-sustain cable, so I can't leave power to only X board without havin also the y-sustain connected)


???

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

Also, the green led on the logic board blinks with the following pattern:

5 seconds ON
2 seconds OFF

Jay

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

Also, the green led on the logic board blinks with the following pattern:

5 seconds ON
2 seconds OFF

Jay

Isn't that pattern for the TV protection mode?

If so is that exclude the psu from the list of culprit?

[tom66]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

5-2 can be PSU but check Vs/Va and if that is low/bad then that may be an issue.
In protect mode, it should become briefly available then go away.

[MagicSmoke]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

The resistor is for jumping the PS-on signal to 5vstby to power on, not for a load. You can use wire but it makes the VS volts read high.

Main board connector disconnected, this is where the resistor will go. Most Samsung psu's jump ps-on to 5.3v stby to force on. It actually only needs > 2.5v that's why the resistor is needed. Some also have a VS-on that needs a jumper also.

According to pic here http://assets.shopjimmy.com/media/ca...330a-top_1.jpg

You need to jumper CN802 pins 1 & 2 with Pins 5 & 6 w/ 1k resistors to fully power up psu. No connections to other boards.

Then check for 15v on CN801 and VS & VA volts at their test points.

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

5-2 can be PSU but check Vs/Va and if that is low/bad then that may be an issue.
In protect mode, it should become briefly available then go away.

When I power ON the TV, the voltage seems to start at their nominal DC voltage, but rapidly drop to 0VDC in about 10-20 seconds.

I.E,
Vs starts at about 200VDC and drops to 0VDC in a few seconds.
Va starts at about 50VDC and drops to 0VDC in a few seconds.

That seems to be what you are describing?

So this would indicate the power supply is healty and the problem would be elsewhere?

Jay

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

The resistor is for jumping the PS-on signal to 5vstby to power on, not for a load. You can use wire but it makes the VS volts read high.

Main board connector disconnected, this is where the resistor will go. Most Samsung psu's jump ps-on to 5.3v stby to force on. It actually only needs > 2.5v that's why the resistor is needed. Some also have a VS-on that needs a jumper also.

According to pic here http://assets.shopjimmy.com/media/ca...330a-top_1.jpg

You need to jumper CN802 pins 1 & 2 with Pins 5 & 6 w/ 1k resistors to fully power up psu. No connections to other boards.

Then check for 15v on CN801 and VS & VA volts at their test points.

Ah ok, so it's like a PC power suppy, where you ground a wire to let it fire up...

Sorry, i misunderstood the instruction in the first place...

So basically, I disconnect all connectors from the power supply and short (using the resistor) the specified pin to activate the power supply.
Then I should be able to verify the different output voltages to see if they are at their expected levels?

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

So basically, I disconnect all connectors from the power supply and short (using the resistor) the specified pin to activate the power supply.
Then I should be able to verify the different output voltages to see if they are at their expected levels?

Do I need to leave the CN801 cable connected to power on the tv?
If I don't, I can't turn the TV on ... Do I need to also drive the PS-ON of the CN801 cconnector?

[tom66]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

PS-ON needs to go LOW (active LOW), VS-ON goes HIGH (active HIGH) this will turn on low voltages and high voltages (~200V, ~60V Vs/Va)

This is for Samsung, it is different for other brands, most use active HIGH for both PS-ON and VS-ON.

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

PS-ON needs to go LOW (active LOW), VS-ON goes HIGH (active HIGH) this will turn on low voltages and high voltages (~200V, ~60V Vs/Va)

This is for Samsung, it is different for other brands, most use active HIGH for both PS-ON and VS-ON.

All right,

So for the connector CN802
- PS-ON : pull down (gnd using 1K resistor)
- VS-ON : pull up (high 5.3V using 1k resistor)

For the connector CN801, there is also a PS-ON.
Do I use a pull down also for that pin, or should I simply left the cable connected to the main board?

Regards.

[tom66]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

There's one thick cable going between main A/V board and power board, disconnect that and jumper anything required on there. Disconnect the connector between the control board (also called logic board, small green board usually below power board) and power board too.