Panasonic Th-42A400z led tv

[lambchopsnz]

Ok I was given this tv and all i knew was it dosent go.. so i plugged it in and the standby light goes from green then starts to flash once every second or so,not sure if this is the same as a plasma blink.
Anyway i have found it very hard to find any info at all about this tv.
I have tested the standby voltage on the power board which reads 5.2v so im guessing close enough to the 5.3v on label but the 16v test point reads 0v as does the 35v.
I then removed the power board and discovered a heated patch on the board around one of the FETS which i have replaced but still have the same result...So would be grateful if anyone could give me a few pointers on what to check next..could it be a different board thats the problem?
Im In New Zealand So i know the z at the end of the model number is for New Zealand area.
I will add some pics when i can figure out how to get them on here from my phone.
Thanks For any help.
Nick.

[R_J]

Re: Panasonic Th-42A400z led tv

One blink= BL_SOS -- SOS from PANEL inverter

check for +16 volts on TP7404 or cathode of D7409 or across C7423
check for +32 volts on TP7401 or cathode of D7402 or across C7422
If you have +5V5 you have +16v
If the voltages are at these points then power supply is likely working but is being shut down.
check the voltage on P2 pin 9 or TP7416 which is SUB_ON

[lambchopsnz]

Re: Panasonic Th-42A400z led tv

Here's some pictures I will edit this post soon

[lambchopsnz]

Re: Panasonic Th-42A400z led tv

OH Hell I give up on posting..
Hi RJ,
Thanks for your reply this is now my 3rd attempt at posting so its going to be short lol
I tested all points shown on those boards in post above (i couldnt edit it) the voltages were correct until the led blink kicks in where they drop to 0v except the 5.3v which dosent change.
The last picture just indicates the heated area on the board and FET I replaced (TK10A60W)
Hope to hear back with some more ideas
Cheers
Nick

[dick_barton]

Re: Panasonic Th-42A400z led tv

Don't know how close this manual is to your set but may be useful.

[R_J]

Re: Panasonic Th-42A400z led tv

Do you get a flash of the backlights at all when you try to turn it on, The problem may either be on the LD-Board or it could be with the panel led's
Check the voltages on LD2 plug, or at the test points SRV-VLED1 & SRV-VLED2, you will need to turn off then back on to see if you can measure the voltage before the board errors and shuts down.
The brown area around the fet is just discolorization from heat, the fet runs a bit hot, this is normal and occurs all the time.

[lambchopsnz]

Re: Panasonic Th-42A400z led tv

Yeah there is a flash of lights I can see through the holes in the back.

[R_J]

Re: Panasonic Th-42A400z led tv

Then its a good guess that the power supplies are ok and there's one or more bad led's, If you do disassemble the panel, be very carefull and mark which way the diffuser sheets go. and try not to seperate them, this will make reassembly much easier.

[lambchopsnz]

Re: Panasonic Th-42A400z led tv

Thanks again for your help I tested the voltages at SRV-VLED1 and 2 With both reading 32V.
How Hard is it to disassemble the panel for a first timer how many layers are we talking?..
I guess the tv cost nothing and its not going so i guess worse thing to happen is it still dosent go right lol.
What about getting replacement strips do they need to be same number etc?
Cheers
Nick

[R_J]

Re: Panasonic Th-42A400z led tv

There will usually be an outer metal or plastic frame, then the lcd panel itself (which is very fragile and is a little bit thicker than a credit card), followed by 2 or 3 thin diffuser sheets and then a heavier sheet, once those are removed you will see the led's which should be mounted on strips but may be behind a white reflector sheet with holes for the leds. Then after all that you will have a choice of trying to find replacement led strips or try and replace the led's them self which is not that easy to do.
Here is a shopjimmy video https://www.youtube.com/watch?v=T2FboV-1PJg
or search videos on google "lcd tvscreen disassembly"

[budm]

Re: Panasonic Th-42A400z led tv

Leave the DCV meter probes on the two legs of the filter cap C7813 (47uF 160VDC) and then turn on the TV while watching the meter to see how high the Voltage jumps up to.
Turn off the TV and then move the meter probes to C7817 (47uF 160VDC) then turn the TV on while watching meter to see how high the Voltage jumps up to.
You can also try having one LED strip connected one at a time to see which one does not come on, you have two Red and two Black wires, each pair (RED/BLACK) per LED string.

[lambchopsnz]

Re: Panasonic Th-42A400z led tv

I tested the voltages on the 2 caps suggested the top one c7813 the voltage got to about 37v the bottom one c7817 i believe 101v was the highest i saw but its that quick its hard to be accurate.

[budm]

Re: Panasonic Th-42A400z led tv

If you're pretty sure that the Voltage only jumps up to 37V on C7813 compared to the 101V on C7817, it means the boost converter where C7813 is not working.
We need to see good clear straight shot pictures of the whole bottom side of that LD board.

[lambchopsnz]

Re: Panasonic Th-42A400z led tv

I tested the two caps again before I took the board off and yeah the top one got to about 39-42v while the bottom was about 87v so definitely a difference hopefully these pictures will help they are taken as though the top screws have been removed and the board hinged down on the bottom ones if you understand that lol
Cheers
Nick

[lambchopsnz]

Re: Panasonic Th-42A400z led tv

Ok it turns out you cant edit posts even though it says edit it wants to create a new reply so here are the pictures the way i first intended on uploading them i hope...

[R_J]

Re: Panasonic Th-42A400z led tv

If you disconnect the LD2 plug going to the panel and check the voltage across C7813 is it still low, or does it come closer to C7817
Needs to be measured while turning on tv as it will error and drop down

[lambchopsnz]

Re: Panasonic Th-42A400z led tv

Hi I tested both C7813 and C7817 with the LD2 plug removed and yeah the voltages did jump up to close to each other.
Nick

[R_J]

Re: Panasonic Th-42A400z led tv

That tells me that one of the two led strings is loading that side of the Ld power supply,
an led tester with current readout would likely confirm it.

[yohnsee]

Re: Panasonic Th-42A400z led tv

Don't know how close this manual is to your set but may be useful.

It was sure useful for me, thanks.

[lambchopsnz]

Re: Panasonic Th-42A400z led tv

Hi Guys thanks for all your suggestions so far so ive got to the point where i need to test the led strips. One of those led testers is about $50 if i buy from ebay or over $100 local,my question is do i still need to pull the screen apart to test the strips or can i test them somehow without spending lots, i do understand if its a strip i need to pull the screen apart anyway.
Im just looking for an easyish solution.
Unfortunately or fortunately i guess im booked in to have eye surgery for glaucoma on the 4th July so wont be a lot happening with the tv for a while anyway.
I will be keeping an eye on the forum and let you all know when im back into it.
cheers
Nick