Samsung PS-42C455 no picture

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

No, I haven't seen any feedback either. So probably the led will blink that fast if proper LVDS is being recieved. I will know when I've checked the LVDS, to be or not to be
Maybe the led blinking frequency is showing when logic board is in sync with incoming LVDS.

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

Yeeaah! This issue has now been solved. Here is what I did:
When disconnecting the control flatcable between Y-SUS and logic board, the LED on the logic board started to blink normally, in other words, at a much faster rate than before.
Also, the VA and VS supplies were not shut down directly after start up.
Aha! This made me again check Y-SUS board very carefully for any abnormal readings in the power sections. Nothing found!
Then I disconnected the Y-SUS board outputs from the Y-BUFFER board, reconnected the control cable and fired up.
Again, normal behaviour of logic board and VA and VS up and running.
Aha! I then suspected a bad Y-BUFFER driverchip and took a close look but couldn't find any. THEN, I saw the issue.
One of the ceramic capacitors for supply decoupling close to one of the Y-buffer driverchips was a little black. Those were covered with silicone so it was hard to see right away. But when I managed to pull the black cap away I could see this measured a dc resistance.
Voila! Problem found. Reconnected everything and fired up the set with good hope.
Set starts, BUT - Screen information is upsidedown!
I had changed the main eeprom on mainboard in earlier repairattempts since I thought the problem was caused by a corrupt eeprom.
I thought that this new eeprom should be rewritten properly during startup, but this wasn't the case obviously.
Luckily I had saved the old eeprom and when putting that back screen returned to normal. The set reported that "mainboard has been changed - open servicemenu to config" and some tweaking in the servicemenu made the set perfectly up and running again.
So this will be the end of this story - nice journey really! thanks for all help, especially tom66 who showed great interest to help!

[tom66]

Re: Samsung PS-42C455 no picture

Yeeaah! This issue has now been solved. Here is what I did:
When disconnecting the control flatcable between Y-SUS and logic board, the LED on the logic board started to blink normally, in other words, at a much faster rate than before.
Also, the VA and VS supplies were not shut down directly after start up.
Aha! This made me again check Y-SUS board very carefully for any abnormal readings in the power sections. Nothing found!
Then I disconnected the Y-SUS board outputs from the Y-BUFFER board, reconnected the control cable and fired up.
Again, normal behaviour of logic board and VA and VS up and running.
Aha! I then suspected a bad Y-BUFFER driverchip and took a close look but couldn't find any. THEN, I saw the issue.
One of the ceramic capacitors for supply decoupling close to one of the Y-buffer driverchips was a little black. Those were covered with silicone so it was hard to see right away. But when I managed to pull the black cap away I could see this measured a dc resistance.
Voila! Problem found. Reconnected everything and fired up the set with good hope.
Set starts, BUT - Screen information is upsidedown!
I had changed the main eeprom on mainboard in earlier repairattempts since I thought the problem was caused by a corrupt eeprom.
I thought that this new eeprom should be rewritten properly during startup, but this wasn't the case obviously.
Luckily I had saved the old eeprom and when putting that back screen returned to normal. The set reported that "mainboard has been changed - open servicemenu to config" and some tweaking in the servicemenu made the set perfectly up and running again.
So this will be the end of this story - nice journey really! thanks for all help, especially tom66 who showed great interest to help!

Glad you fixed it! That is a really, really strange issue - I have never heard of that before.

For resetting the EEPROM you can usually go into the service menu and select Factory Reset.

[JonathanAnon]

Re: Samsung PS-42C455 no picture

Sorry for digging up an old thread, but I have one of these in with the same fault... Power comes on, audio sound comes on, but no picture...

I've tried disconnecting the same boards, but the voltage still drops across the Va and Vs pins. Even when I disconnected the Y board from the PSU (so only the logic board and the video board are connected to the PSU) the Vs and Va pins initially go high before dropping.

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

Hello!
If memory serves me right, when disconnecting boards, the controller will shut down VA and VS by protectmode.
I would connect all the boards again and restart troubleshooting.
Does the statusled on the logic board blink slowly aswell?

[JonathanAnon]

Re: Samsung PS-42C455 no picture

Hey there, thanks for your response. I think you're right about the automatic shutdown. I googled the PSU number and found this thread, with a similar TV,

http://www.justanswer.com/tv-repair/...za-plasma.html

The expert on that site suggested replacing the PSU when they noticed that the voltages were dropping with the y boards unplugged (assuming as I was that the power was dropping because of a fault independent of any external board). The TV owner bought the new PSU, and the same thing happened. He sent that PSU back, got ANOTHER one and that did the same too!!!!!!! So I'm pretty satisfied that the PSU is good.. And I'm very glad I found that thread.

My logic board has the same 0.3Hz LED frequency. Gave a check of the cermaic caps you had the fault with and they dont look black

[tom66]

Re: Samsung PS-42C455 no picture

See here. The PS-43D450 (similar to PS-42C455) will shut down if Y-main or X-main are not working.
https://www.youtube.com/watch?v=wmJenmz9vro
https://www.youtube.com/watch?v=8cMfgBvaDuo

On this chassis it -may- be necessary to replace both X-main and Y-main at the same time due to how the boards are chained.

People on JustAnswer are not worth the money; I honestly think the site is a scam. That guy actually seemed to have an idea -- pretty uncommon there though.

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

I remember this was a pretty easy chassis to work on, even if I next to got crazy before finding the blown ceramic cap on the buffer board.
Did you measure the Y and X board powercomponents for shorts?

[tom66]

Re: Samsung PS-42C455 no picture

Yeah, I found numerous fets on both had failed; the only conclusion I could make was that one board had damaged the other.

[JonathanAnon]

Re: Samsung PS-42C455 no picture

okay I observed the following:

Disconnecting the X board from the Y board -
Plug in, relay clicks on, makes the intro sound, LED flashes at 0.3Hz, no picture.

Disconnecting the Y buffer board from the Y board, X board disconnected -
Plug in, relay clicks on, makes the intro sound, LED flashes at 0.3Hz, no picture.

Disconnecting the Y board from power supply altogether (i.e. no X or Y connected) -
Plug in, relay clicks on, makes the intro sound, LED flashes at 0.3Hz, no picture.

same every time.

I've checked all the pins on Y board and X board and there is no short. Trying to get out the Y board so that I can test the FETs, but I cant disconnect the logic cable... I really dont want to damage it but it's not budging.. tried flipping it UP with small screwdriver and pulling it OUT then UP.. I'll have another bash tomorrow.

[tom66]

Re: Samsung PS-42C455 no picture

To remove that logic board connector you just need to lift the latch then carefully remove the cable.

Are you saying as long as the X board is unplugged the set will boot properly?

[JonathanAnon]

Re: Samsung PS-42C455 no picture

Are you saying as long as the X board is unplugged the set will boot properly?

No Tom, I havent got the TV picture to boot at all. It basically demonstrates the same characteristics with any combination of the X and Y boards plugged in or out of the power board. I'll try and safely extrude the Y board tomorrow and check the FETs you were talking about.

[tom66]

Re: Samsung PS-42C455 no picture

I'd force PSON low using a 100 ohm resistor, unplug control->LVDS cable, then jumper pins 3-4. You should see test patterns.
http://www.youtube.com/watch?v=JCtF5...ature=youtu.be

This is probably the all too common main board problem that newer Samsung are having.

[JonathanAnon]

Re: Samsung PS-42C455 no picture

okay that sounds like a good idea..

Just to clarify, I connect the PS_ON on the power board to ground with 100 ohm resistor, disconnect the LVDS cable from the main board to power board, and jump pins 3-4 on the power board... And if I get the test pattern, this verifies that Y board / X board / screen are working.

[tom66]

Re: Samsung PS-42C455 no picture

Just to clarify, I connect the PS_ON on the power board to ground with 100 ohm resistor, disconnect the LVDS cable from the main board to power board, and jump pins 3-4 on the power board... And if I get the test pattern, this verifies that Y board / X board / screen are working.

No... disconnect LVDS from Main to Control.
Jumper pins 3-4 on debug connector on Control... see picture.

[JonathanAnon]

Re: Samsung PS-42C455 no picture

that's very helpful thanks.

Just thinking about it, that jumping PS_ON to ground (through the 100k resistor) is pretty much the same as the way as you used to turn on a PC ATX power supply by jumping pin 14 (green) to ground. Must try that trick on a few of the other TVs I have sitting in my garage.

Will report back tomorrow. :-)

[PowerAmpFreak]

Re: Samsung PS-42C455 no picture

Please make a voltage measurement across the ceramic caps on the y-buffer boards when forcing set to start. Ceramic caps can fail without visible traces, small cracks.
Your story sounds so much like mine so why not check this before going into deep troubleshooting.

[JonathanAnon]

Re: Samsung PS-42C455 no picture

Your story sounds so much like mine so why not check this before going into deep troubleshooting.

Yeah it sounds similar. BUT when you disconnected the y buffer board, it changed the LED lighting pattern. This did not work for me.

The first thing I did was look at the ceramic caps across the Y buffer board, but I didnt see the carbon that you spotted.. I removed some of the silicon as well but they all seemed fine.. I will measure the voltages across them when I force it on..

sorry just edited this:

[JonathanAnon]

Re: Samsung PS-42C455 no picture

okay, I did as tom suggested,
- disconnected LVDS cable from logic board to main board.
- jumped 3-4 on the logic board.
- jumped the PS_ON on the power board to ground.
I plugged the TV in, relay clicks on, and then the LED starts going at the same 0.3Hz... No test picture comes on.

I pulled out the y board and started testing the FETs. I found two FETs that were measuring strangely so I pulled them out to test properly.. Both are.. RJP30E2 762082 ... I cant find a datasheet for this, but on diode test I get no measurement on either FET on any combination of the pins.. However when I test for continuity between source and drain and apply a voltage across the source/gate pins, the resistance goes to zero.. Is it possible for the diode in the FET to fail, but it still to turn on when a voltage is applied across to the gate.. ?

There is an RJP30E2 761082 on the board also, which I assume is the PNP version of this FET, and it measures 0.54v across it's source and drain pins on diode test..

[tom66]

Re: Samsung PS-42C455 no picture

Those are not FETs. They are IGBTs, which do not have to include a diode (a FET has it intrinsically built into the structure, it cannot be removed.)