42LK450-UB Noob question

[newkidontheblock]

Ill start with my TV problem. I have stated above what my Model LG tv i have.
With that said, It has a strange problem I have not seen in any TV repair I have done.

I've repaired maybe 5 or so TV's, but all with completely obvious issues.
No Power at all-checked and changed fuse
Intermittent power - bad caps, replace capacitors

Easy stuff like that

Well this one im working on, It has power. Every Pin i test is getting the right voltage. So my ignorant self just replaced the main board thinking that has to be it.. anywayy..

TV Issue: Has power, the standby light is red until pressed then turns blue. The LG Logo splashscreen turns on for a few seconds then goes out. Then a screen stating what the current channel the tuner is on (hdmi1/hdmi2/tv ect...) Then it goes back out, then goes to an LG Logo screen that says no signal and turns off. But its rhythmic in a way of about 2 seconds per screen. Then the standby light fades back to red.

What I have done:
Replaced all boards with ones from Shopjimmy.com (Main board, T-Conn, and PSU)

What could this possibly be? The screen is fine, the back light is lit as im getting proper signal it just shuts off. Any ideas? I am officially stumped. I even made a profile here to ask the professionals as they have helped me with other TV's (just by using the forums, people have solved the same problems i had)

Thank you so much for any time given to me. It's my Dad's Tv, and as you know he keeps nagging me asking where its at.......

[budm]

Re: 42LK450-UB Noob question

"Every Pin i test is getting the right voltage."
So are you saying the control signal pins ALL have correct Voltages? Are 100% sure?
You need to list all the Voltages at the power supply connector that goes to the main board, you MUST PUT DOWN THE PIN NAME and follow by the Voltage reading of each pin when the TV is in stand by and after the TV is turned on.
How about the pictures of the whole back side of the TV showing all the boards?

[Nick's Tvs]

Re: 42LK450-UB Noob question

Not sure how you got a main board from shopjimmy as these guys are notorious for being impossible to buy anymore. But what you are describing sounds like a classic bad main board. Most likely a bad board was sent to you.
Based off my experience you have either software issues or BGA issues.

[newkidontheblock]

Re: 42LK450-UB Noob question

Ok, gotta come clean here.

SO by "I tested all the pins" I mean my Uncle did, but he is in IT. So I would figure he would be ok to trust. Buutttttt.... I would rather be 100% sure myself before i go pouring more money into this.

So, I have a meter that can just amps/volts. Ground to chassis and check pins, but I aint getting squat. I have the Tv plugged in i would assume to get power, but as stated in my post it wont stay on long enough to test all of them.

I guess my newer question would be, how does one check these pins? and i already have the requested pictures, as well as a picture of the pin voltages from the PSU.

Im off to one of the stickies that im sure answers one of these questions i have. Sorry to be an ignorant pain.

[budm]

Re: 42LK450-UB Noob question

"Ground to chassis and check pins, but I aint getting squat. " It is either operator error, meter is bad, or meter setting error.
Well, get a battery and test the Voltage to see what your meter will show on the screen.
What kind of meter and what did you set it to?

[newkidontheblock]

Re: 42LK450-UB Noob question

Alright got it all squared away. I test the pins in both stand by and in the on position. Being as the TV would only stay on for a few seconds really made this fun. So as in the pictures i posted the pins i was testing off the PSU, check out my picture to see my pins

Any ideas what i should do with this now?



Or, what else should i do? I like the previous idea of a bad main board (defect) because thats what i thought in the first place. But im sure if i try to return it as defective they will want proof.

Thanks again for all your help.

[will62]

Re: 42LK450-UB Noob question

The problem may be on your power board. See attached photo. It depends on the microcontroller code, but a LOW signal is usually below ~0.7V.

[budwich]

Re: 42LK450-UB Noob question

disconnect one at a time, the tcon to panel cables and see what the display does when powered up thereafter.

[vinceroger69]

Re: 42LK450-UB Noob question

as this is a older ccfl set i guess it could be a failed ccfl or invertor transformer

[newkidontheblock]

Re: 42LK450-UB Noob question

disconnect one at a time, the tcon to panel cables and see what the display does when powered up thereafter.

Disconnected all cables and booted one at a time. When T-CONN was dissconnected it just flashed the screen on the same 4 times. Just no picture. Reconnected and tried different ones one at a time to the same result as the original. So I cant seem to narrow it down that way

[newkidontheblock]

Re: 42LK450-UB Noob question

as this is a older ccfl set i guess it could be a failed ccfl or invertor transformer

Any easy way to test this theory? Sorry im not that good at this. I have the tools and very basic knowledge.

[newkidontheblock]

Re: 42LK450-UB Noob question

The problem may be on your power board. See attached photo. It depends on the microcontroller code, but a LOW signal is usually below ~0.7V.

I have replaced this board as well, but being as that voltage is rather high, what can I do to narrow it down?

Thanks

[vinceroger69]

Re: 42LK450-UB Noob question

on your second picture where does that bottom wire connector go too?

[will62]

Re: 42LK450-UB Noob question

Looking a little further, it's not the power board. The error signal just crosses the board. As vinceroger69 mentioned above, problem could be inverter/ccfl.

[newkidontheblock]

Re: 42LK450-UB Noob question

on your second picture where does that bottom wire connector go too?

Backlight inverter board

[newkidontheblock]

Re: 42LK450-UB Noob question

Looking a little further, it's not the power board. The error signal just crosses the board. As vinceroger69 mentioned above, problem could be inverter/ccfl.

What could i do to test the inverter? Its only $25, but still. I would like to be sure.

[vinceroger69]

Re: 42LK450-UB Noob question

can you upload a picture of that board so we can see whats fitted as you may be able too run some tests on it

[newkidontheblock]

Re: 42LK450-UB Noob question

Let me get the cover off, and ill drop one. Give me a minute

[newkidontheblock]

Re: 42LK450-UB Noob question

Attached two pictures of the inverter board

[vinceroger69]

Re: 42LK450-UB Noob question

what you will need to do is test the windings on each of those transformers is there a part number on them? can you take a clear photo of one of them