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info tech
info tech, Technician
Category: TV
Satisfied Customers: 15633
Experience:  Television Engineer for many high street outlets 20 plus years experience
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I have a Panasonic tx-42a400b tv, when it turns on green

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Hi, I have a Panasonic tx-42a400b tv, when it turns on green power indicator comes on, few seconds later sound then when you expect the screen to turn on it turns off and power indicator flashes red.



Is the light blinking and pausing red please?


Customer: replied 1 year ago.
the light flashes red and off red off... slowly
Customer: replied 1 year ago.
I replaced the main power supply board. Which did not fix it. And then the LCD board, which did not fix it

So thelight is blinking and pausing please count the amount of red blinks between pauses please like 3 blinks pause 3 blinks as an example?


Or is it continuos blinking?no pause

Customer: replied 1 year ago.
Ok, please give me 2 minutes. I just have to put the new LCD back in. Took it out as to return it. One moment.


Customer: replied 1 year ago.
Customer: replied 1 year ago.
Red light stays on for approx one second then stays off for about 4-5 seconds
Customer: replied 1 year ago.
Then repeats continuously

You have replaced wrong boards how old is the set please?

Customer: replied 1 year ago.
Roughly 3 years at a guess.
Customer: replied 1 year ago.
Maybe 2

The set is not booting you need to replace the mainboard that is the one with all the AV input connectors attached, you need to get the part-number from the board itself and use that

Let me know if you need more help

Please consider rating the answer positively with the rating bar of stars at the top of the page,rating me positively enables me to receive payment from the site (Iam a user of the site like you are a verified technician, I do notwork for JustAnswer) if you need more help let me know , note thequestion NEVER CLOSES IT REMAINS OPEN should you need more help no or later thank you.

Many Thanks


info tech and other TV Specialists are ready to help you
Customer: replied 1 year ago.
Ok thank you Anthony! That would have been the last board I tried due to sound coming through. I figured it must be at least part working.
I'll take your word for it though.
5 stars!
Customer: replied 1 year ago.
Hi Anthony, are you online?

Yes here

Customer: replied 1 year ago.
I replaced the main at board, but pretty much the same issue only this time when turning on white lines flash vertically just off centre to the right and the tv powers off... led showing same sequence as before, any ideas?
Customer: replied 1 year ago.
av board
Customer: replied 1 year ago.
just to clarify all boards been replaced except timer board, think it's a screen issue?

Does the sound stay on ALL the time or does this go off too when it powers down?

Is the part-number exact as original main-board?

Customer: replied 1 year ago.
Part numbers are exactly same
Originally the sound would come through and then just when you would expect the tv screen to turn on it would power off.
Since replacing the av board no sound is heard.
Customer: replied 1 year ago.
Originally when tv powered off and red led started blinking the sound would have stopped too

The board you got should have exactly the same symptoms as your old board if the fault is elsewhere (which I doubt) so if that is not the case send that board back as its bad, this is not unusual I get about one board in every 4 or 5 bad because they are pulled from scrap sets new boards would not be viable

If they dont have another look elsewhere

Customer: replied 1 year ago.
OK thank s Anthony, wouldn't mind but paid extra for fast delivery! Typical. I'll try a new av board. Thanks again

I still think this is a mainboard issue it could be bad backlights but if that was the case you should see some indication on the display

A new main may be costly we all fit pulled boards in this industry

Customer: replied 1 year ago.
The display just goes black and since new (faulty av board) white lines flash on screen then goes black
Customer: replied 1 year ago.
I'll try a new used main boards.. see what happens

No you should have same symptoms you see that is logical because if the mainboard is good and that board is good should be same symptoms fault elsewhere, but that is not the case there are different symptoms with replacement board so it should either work or show same symptoms as existing board that is not happening

Customer: replied 1 year ago.
Good logic! Stands to reason really. I'll give it a shot. Thanks again

Your Welcome

Customer: replied 1 year ago.
Hi Anthony, sorry to keep bothering you with this.I tried 2 more av boards and the same problem is there.. so I have 4 boards now. Strangely when I put the original one in sound comes through when the tv starts to turn on.But I think we can rule out it been a main board? You mentioned it could possibly be bad back lights, is this something that is worth trying to fix?I'm going to buy a new tv now anyway but would like to fix this one if possible.
Appreciate your help and advice.

No really its no bother so please do not concern yourself with that

I really think you are not getting the correct mainboard logically it does not make sense , if the fault was elsewhere and you are sticking in exactly the same board,,,,,, should you not have EXACTLY the same symptoms,,,,,,?have a think about that because I believe you should.

Usualy this is because the boards are different in one way or another or fault

Customer: replied 1 year ago.
I understand what your saying, and it does make sense.However I have four identical boards now, serial numbers etc. I was keeping track of the original one at one point, now I couldn't tell you which one it is. Only way I can tell is putting them in in turn and finding the one that allows sound to come through when the tv tries to turn on.Which in itself is really odd and like you, leads me to think the fault is with the board.But.. I'm just speculating now.. the tv has built in free view. Which board is responsible for that? Could it be that the original board is already.. "tuned" and the other 3 are not??Meaning that one goes straight to allowing channels through, the other 3 go to setup screen? Obviously the tv dies long before that actually happens.You know far more than me and I'm just guessing.But either I have four broken boards (which is possible), the wrong boards for the tv (which is unlikely in my opinion as all serial numbers are the same and they look identical) or.. something else?Do the boards get "paired" with the rest of the system when the first turn on.. or perhaps tuned?I realise I'm just waffling and know very little.Just if all 4 boards are fine and the fault is somewhere else, is there a logical reason why the original one allows sound through and the other 3 don't?Many thanks again Anthony.

Yes the light flashes red and off red off... slowly <<<<<you are very sure its just one blink pause one blink etc?

Which did not fix it. And then the LCD board, which did not fix it <<<what do you mean by LCD board?what board are you referring to?there is no board called an LCD board?are you referring to maybe a separate LED driver board?

This set is your own set?it was originally working well?you have not picked this up from somewhere?

Can you take photos please first of the inside of the set with all boards then of the two mainboards you have ,use the paperclip on your toolbar thanks


Customer: replied 1 year ago.
the led board is what I meant. And yes this is a tv I bought brand new from curries 2 - 3 years ago.. also the power led does just blink on off on off.. on for about 1 second off for about 4.I'll take some photos now.


By the way for your re-assurance I am in the UK myself near Warrington


Customer: replied 1 year ago.
Back of tv
Customer: replied 1 year ago.
3 av boards, (plus one in tele)
Customer: replied 1 year ago.
These are all the parts I've changed. Plus there's one of each still in the tele.
Customer: replied 1 year ago.
The only board I haven't changed is the one bottom centre. Thats the timer board, I think?

Yes that is the tcon board but I would not have thought it would cause this issue, please as a test just pull out the input to it from the mainboard and let me know if there is any change in the sets behaviour, I am referring to the ribbon lead going into it from the mainboard, the set ordinarily will go off anyhow if it was working however I am looking for a change in behaviour, I still though think two things either the main-boards you have are all somehow bad in one way or another OR there is a backlight problem and that would be very bad news, unfortunately there is no way or effective way to check either

Let me know about the tcon check

Customer: replied 1 year ago.
No change in behaviour. Could this be the problem then?

Let me just say its not impossible for the tcon to be causing this but I would expect a change in behaviour if the tcon is bad, I would not ordinarily be suspecting this board at all as the cause anyhow, where are you getting the mainboards from please?

Also do the same with the LED driver board disconnect it and fire the set up let me know if there is any change

Customer: replied 1 year ago.
I bought them off eBay. Perhaps not the best place although all said tested and fully working.. Would you recommend another site?Having said that I have just seen a tcon board on eBay for roughly 10pound pp included, worth a shot?

Have you tried or

I dont like ebay for this

Customer: replied 1 year ago.
I am going to buy a new tv anyhow now. But seems a real shame to let this one go. It's the first decent tv I bought for myself, attached to it!!

The only other catastrophic thing is the LED backlights , please let me know about the LED board disconnect and any behaviour changes

So what will happen is the backlights wont be driven and you should get a longer start up sequnce to maybe a green light of 15 to 20 seconds before shut down

This will tell me the backlights are bad that is bad news if so

Customer: replied 1 year ago.
Ok, just to clarify, I am disconnecting the cable on the left of the led board that runs to the power board?

Yes thats it, then fire up the set note any changes

Customer: replied 1 year ago.
Ok.. so no real change. Other than that when the led driver is connected some sort of flash is seen on the screen. Obviously this doesn't happen when led driver is disconnected.As for the power light its the exact same sequence regardless. So this means backlights are not the fault?

No it could be the backlights are bad as I say unlike CRT sets where everything was checkable on flat panel its mainly an eleimination exercise some checks are made but in the main elimination done by gained experience, the backligyts are in arrays so it could be there is an array bad, the only way to prove that is by taking the panel apart and examining them not recommended

I still have a doubt however about your mainboards

Customer: replied 1 year ago.
Ok, I'll buy another av board from the site you recommended and possibly a tcon board just to rule it out. Then i'll scrap it if that doesn't fix it. At the very worst at least I learnt a little.Once again, thanks Anthony.

I would bet its the mainboard and the ones you got from ebay are bad this is not unusual I have hed incidences of this before