Samsung PS-42C455 no picture

[tom66]

Re: Samsung PS-42C455 no picture

I already tried this, but there are several EEPROM's on the mainboard, so don't know if I made at the correct one.
It sure looks like there are some hokus pokus with the mainboard, in some cases when set is turned on, the standby led is on, and when in standby led is off. Should be other way around.
I want this bastard to be reset now !!!

The odd standby LED is normal, a 40" LCD I have here does the same thing.

Try all eeproms except the ones near HDMI or VGA ports.

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

The odd standby LED is normal, a 40" LCD I have here does the same thing.

.

Ok, so that's not an indication of a corrupt mainboard? Oh well.

Pins 5 & 6 on the EEPROMS is the SDA and SCL lines, does the mainboard processor check if those are shorted during start-up and IF they are, the EEPROM contents is initialyzed?

[tom66]

Re: Samsung PS-42C455 no picture

Pins 5 & 6 on the EEPROMS is the SDA and SCL lines, does the mainboard processor check if those are shorted during start-up and IF they are, the EEPROM contents is initialyzed?

No, I believe doing so causes it to think the EEPROM is empty, so when it starts booting up it rewrites the memory.

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

I appreciate your ultrafast response Tom!
I'm the kind of guy who don't like to wait - so that suits me brill!

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

Well, bad news, I don't succeed to write new eeprom data by shorting SDA and SCL during start-up, tried XX times with different timing.
There are 3 EEPROM's across the board, one is marked MAIN EE, SUB EE, and the third is close to the VGA and HDMI inputs. This one I didn't touch.
But I tried shorting SDA and SCL on both MAIN EE and SUB EE (not at the same time though) without any luck. The short was made with a switch so shorting is guaranteed.
Then I replaced the MAIN EE. First start-up the set behaved little different, it shut off by itself after ten seconds which I thought was a result of it's own powercycle and reset, but no.
Everything is the same... BAH!!

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

I might be troubleshooting the wrong board. Most things indicates that main board actually is alright, but what the H**L could this be else.
Read through two different service manuals for this panel (Samsung F71A) without getting something useful.
The manual refer to a control led on the logic board. This led is blinking slowly, at a rate around 0,3Hz. The service manual doesn't tell if this is correct or not, it just tell that this led should be checked for normal operation.

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

If there was a problem with the LVDS output from mainboard, would this perhaps automatically turn off VA and VS in order to protect the panel from possible burn-in problems?

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

I now disconnect the LVDS cable going to logic board. The LED on the logic board blinks in exactly the same way as with the cable connected.
- Either there is no LVDS from mainboard
- Either the logic board is faulty
- Either the LED does not indicate LVDS status

[tom66]

Re: Samsung PS-42C455 no picture

I now disconnect the LVDS cable going to logic board. The LED on the logic board blinks in exactly the same way as with the cable connected.
- Either there is no LVDS from mainboard
- Either the logic board is faulty
- Either the LED does not indicate LVDS status

Maybe flashing LED indicates fault? Does it blink a number of times, then stop, then blink again...? The only way you could know if there is LVDS is check with a scope.

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

It's terrible how bad the service manuals are for those plasmas. They can't even tell what LED indicates
It's blinking continously at a rate about 0.3Hz
I will hook up the scope and check the LVDS.
There is a signal from mainboard to logic board which is called "PDP GO", which I would assume means that panel boards should be turned on.
This signal goes high when set is turned on, and is on until set is turned off by remote.
Then, from logic board to power supply there is a signal "VS ON" which actually turns on VA and VS supplies.
So in other words, it seems like when the logic board recieve "PDP ON" from mainboard it starts up VA and VS.

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

If anyone of you out there has a Samsung plasma in the PS42C450 model range, could you perhaps see if it's possible to see the led on the logic board through a ventilation slot, if it's blinking, continously on or off during operation. This would be great help!

[tom66]

Re: Samsung PS-42C455 no picture

If anyone of you out there has a Samsung plasma in the PS42C450 model range, could you perhaps see if it's possible to see the led on the logic board through a ventilation slot, if it's blinking, continously on or off during operation. This would be great help!

I had a C450 a couple of months ago and I seem to remember the light didn't blink - but don't trust my memory!!

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

The service manual does only tell: Check if LED on logic board is normally operating. Something tells me that a normally operating led doesn't blink, right?

[tom66]

Re: Samsung PS-42C455 no picture

The service manual does only tell: Check if LED on logic board is normally operating. Something tells me that a normally operating led doesn't blink, right?

Did you check LVDS with scope?

[tom66]

Re: Samsung PS-42C455 no picture

Here is where I fixed my TV.... maybe there is something useful here

https://www.badcaps.net/forum/showth...hlight=samsung

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

Did you check LVDS with scope?

Nope, I will check this on Saturday.

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

Here is where I fixed my TV.... maybe there is something useful here

https://www.badcaps.net/forum/showth...hlight=samsung

Great, but this failure is not like mine in any way.
Since the VA and VS supplies is shutting down after one second I don't get even a faint picture (of course). Measured across both Y and Z without finding any abnormal readings in the power sections.

[tom66]

Re: Samsung PS-42C455 no picture

Great, but this failure is not like mine in any way.
Since the VA and VS supplies is shutting down after one second I don't get even a faint picture (of course). Measured across both Y and Z without finding any abnormal readings in the power sections.

Yeah, I know - but I've got a video up.

http://www.youtube.com/watch?v=Bmu12mCOKcU

The LED flashes on that one but it's quite fast. (Right near the beginning.)

If so maybe the 0.3 Hz flashing indicates a fault? My set was still "working" other than the picture was screwed due to Z-sus fault.

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

Aha! You're right. You're led is blinking much faster. Thanks!
The moment VA and VS supplies is turned off match the first time LED go off.

[tom66]

Re: Samsung PS-42C455 no picture

That was with a faulty Z-sus but I don't think there was any feedback to the PDP control board. I can't remember if it behaved the same after being fixed, but I suspect it would.