Samsung PS-42C455 no picture

[PowerAmpFreak]

Got a 42" Samsung plasma model PS-42C455 manufactured in december 2010 which does not display a picture. The sound appears to be good though.
(The start-up melody can be heard)
Measured powersupply voltages OK. The set tries for about one second, during this time there are proper Y-sustain and X-main waveforms. The green led on the logic board flash slowly which should be an OK sign of getting proper LVDS.
According to owner the set operated only for about 3 hours from new. He got the set from a shop going bankrupt so warranty is out.
All "power parts" of the set "seems" to work properly. Any advice?

EDIT: Has done the usual troubleshooting by disconnecting power boards, without any difference...

[tom66]

Re: Samsung PS-42C455 no picture

Is there an AC detect pin on the PSU?

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

Let's see, if there is an AC detect pin on the powersupply?
Could you specify what you mean?
The powersupply fires up, PFC comes up, VA and VS on for a second, then shuts down, just like when overloaded and protection kicks in.
But there seems to be no overload issue.
The P/N of the psu is BN44-00329A.

[tom66]

Re: Samsung PS-42C455 no picture

Let's see, if there is an AC detect pin on the powersupply?
Could you specify what you mean?
The powersupply fires up, PFC comes up, VA and VS on for a second, then shuts down, just like when overloaded and protection kicks in.
But there seems to be no overload issue.
The P/N of the psu is BN44-00329A.

I had an LG plasma with the same problem. Fired up, Vs/Va came up, waveforms on both boards appeared, then "CLICK" (from relays) and it went off. Mine repeated the cycle every 5 seconds or so. I found the AC Detect line (which tells the main board the power is still plugged in and to continue operating the TV) was collapsing after a couple of seconds - never entirely figured out why - but I just bridged the optocouplers responsible for the signal and it fixed it.

The pin may be marked "AC-DETECT", "ACD", "AC-ON", "LINE-DETECT", etc... It will go to the main board.

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

Well, if this was the problem in my case I don't see why the audio still works...
The service manual doesn't give any better advice then replacing complete boards.

[tom66]

Re: Samsung PS-42C455 no picture

Well, if this was the problem in my case I don't see why the audio still works...
The service manual doesn't give any better advice then replacing complete boards.

It depends, I've only serviced one Samsung plasma and that had a Z-sustain board problem.

Just check the ACD voltage if there is one.

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

There are no ACD or other kind of LINE DETECT signals going out from the powersupply. It doesn't matter if all powerboards are disconnected. The set behaves exactly the same.
At power up - a signal called "PS ON" (powersupply on) goes high. Relay clicks, PFC comes up. Then a signal called "VS ON" goes high, starting up VS and VA converters. VA and VS reach correct levels. Output waveforms from driveboards comes on, a second later, signal "VS ON" goes low.
Just like if a voltage level detector cannot confirm the VS has reach sufficent level.
Signal "PS ON" is high after this and the set is on producing only audio.

[tom66]

Re: Samsung PS-42C455 no picture

There are no ACD or other kind of LINE DETECT signals going out from the powersupply. It doesn't matter if all powerboards are disconnected. The set behaves exactly the same.
At power up - a signal called "PS ON" (powersupply on) goes high. Relay clicks, PFC comes up. Then a signal called "VS ON" goes high, starting up VS and VA converters. VA and VS reach correct levels. Output waveforms from driveboards comes on, a second later, signal "VS ON" goes low.
Just like if a voltage level detector cannot confirm the VS has reach sufficent level.
Signal "PS ON" is high after this and the set is on producing only audio.

Try pulling VS ON high permanently with a 1k resistor. See if TV stays on. If so could be corrupted EEPROM or detecting a fault? Strange there is no AC detect as most Samsungs have it.

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

Try pulling VS ON high permanently with a 1k resistor. See if TV stays on. If so could be corrupted EEPROM or detecting a fault? Strange there is no AC detect as most Samsungs have it.

Thought about that, but it may result in more trouble if VS shuts down for a reason. I've checked the Y-SUS and Z-SUS very closely and there are no abnormal readings in the power sections of the boards. I like this set, because there are are no hybrid IPM. Everything's built discrete.
All labeled voltages I can find measure according to spec, so obviously it seems safe to pull VS high by external circuitry and see if the picture looks ok or not.
This could aswell be a way to reset the mainboard through service menu, as soon as I get a picture to look at. I thought about corrupted EEPROM aswell, but I don't know how to refresh the data. On other Samsung's I've been forced to replace the EEPROM, then a factory reset begins and store new data at first startup.

[tom66]

Re: Samsung PS-42C455 no picture

Thought about that, but it may result in more trouble if VS shuts down for a reason. I've checked the Y-SUS and Z-SUS very closely and there are no abnormal readings in the power sections of the boards. I like this set, because there are are no hybrid IPM. Everything's built discrete.
All labeled voltages I can find measure according to spec, so obviously it seems safe to pull VS high by external circuitry and see if the picture looks ok or not.
This could aswell be a way to reset the mainboard through service menu, as soon as I get a picture to look at. I thought about corrupted EEPROM aswell, but I don't know how to refresh the data. On other Samsung's I've been forced to replace the EEPROM, then a factory reset begins and store new data at first startup.

If you get the set to boot up and show a picture, turn it off, and while off press Info-Menu-Mute then Power to get to the service menu. Then locate the factory reset and activate that.

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

If you get the set to boot up and show a picture, turn it off, and while off press Info-Menu-Mute then Power to get to the service menu. Then locate the factory reset and activate that.

Yes, that would be nice. I hope this set also has that famous remote sequence to get into the service menu.

[tom66]

Re: Samsung PS-42C455 no picture

Yes, that would be nice. I hope this set also has that famous remote sequence to get into the service menu.

Every Samsung from an CRT RPTV to 6 month old plasma I have seen has had that sequence to enter the service mode.

[selldoor]

Re: Samsung PS-42C455 no picture

If I have the right schematic on page 4 1c0802 PIC16F882 has AC Detect on pin 21?

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

Thanks a lot for the PSU schematics. I tried to find this, without any luck.
Now I can verify if there are any control signals that doesn't reach the PIC processor.
The VS and VA detect inputs at pins 3 & 4 is interesting. Perhaps one of those signals doesn't reach the PIC.
Again, THANKS!!

[tom66]

Re: Samsung PS-42C455 no picture

Nice - Proprietary schematics... where'd you get those?

[selldoor]

Re: Samsung PS-42C455 no picture

One i drew earlier.......

Just searched through 4 pages of Yahoo on the ps board number and
the usual Electrotanya came up trumps. Unusual for a Samsung search.

Only wish i understood them

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

Grrrrrrrrreat!!

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

I forced the VS ON signal constantly on while monitoring Y-SUS drive waveform. This makes then VA and VS up and running, unfortunately the drive pulses is shut down the same time as VS ON goes low, so I will get no picture.
This sure looks like a corrupt mainboard. Wonder if it's possible to make a factory reset without looking at the screen. I remember on a Samsung LE40R86 I changed the EEPROM IC1803 to repair corrupt data, and during first start-up the EEPROM was filled with correct data.
Wonder if it's possible to make the same procedure on this mainboard.
The TV also features upgradeable firmware through USB. I downloaded the new firmware from Samsung's website, stored it on USB stick, and insert in the TV.
The USB stick begin to flash as the mainboard is searching for media (probably), but it's probably necessary to go through a bunch of menu's to really get the TV to update firmware.

[tom66]

Re: Samsung PS-42C455 no picture

It may be possible to short pins 5 + 6 of the EEPROM to reset it, like on some R and M- Samsung LCDs.

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

It may be possible to short pins 5 + 6 of the EEPROM to reset it, like on some R and M- Samsung LCDs.

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 !!!