tv repair not turning on or sometimes

[Dan_68]

Hi all.
A while ago i bought a cheap second 32" plasma. It used to turn on then Fter 5 mins or so the buttons stop working so if u turned it off you would have to wait a few hours for it to come on again. Then it started to not turn on and would eventually after two or three tries. Now nothing. It also had something wrong with red if there was a still image of red it shaked a little bit.
I i have pulled the tv apart. And i think i have found the start of the problem. In the attached photo the top left of the power board there is a cable running to the green board in the middle. The standby voltage should be 5v but is abiut 3v. If i disconnect this cable so the green board isnt connected i have the 5v back. So does this mean the faults in the green board or is it one of those misleqding things that its still in the power board.
Any help would be appreciqted.

 

[(*steve*)]

Was it still under warranty? (I use the word "was" because you've pulled it apart).

The fault could be in the green board, or the power supply (or neither).

You need to check what current is drawn and how that compares to the rated current from the standby regulator.

Does it have similar connections to the red and green boards? Do they draw less current?

 

[Dan_68]

Thankgs. Im not to sure what u mean about checking the current. I guess it cant be the green board as even if it was a complete short circuit it wod be 5v. Would it be high current draw which is making something like a voltage regulator break down.
Thanks i am a mechanical engineer so i have a decent knoqledge but not that of an electrycal engineer

 

[(*steve*)]

No, I was refering to the current drawn by the circuit, not the voltage across it.

You've measured the voltage, so I presume you have a multimeter of some type.

To measure current you place the meter in a current range and insert the meter in series with the circuit. If you've got a plug and socket arrangement like ths the meter connects between the board and one corresponding pin, and you'll have to use a wire or something else to connect the other other pin to the board. Be very careful not to short anything out. Also be very careful not to electrocute yourself as you need to have the TV connected to the mains.

 

[Dan_68]

Thanks, i understand how to measure current. i guess i will have to use wires to connect the other pins.
What im getting at is what if it does or doesnt draw a lot of current, what will that then indicate. I guess i current draw will say a short in the attached board but why does that drop the voltage.

 

[shrtrnd]

I assume you already checked this, but I'll mention it.
Biggest problem I've found on these things lately, is bad power on/off switch itself.
Did you use an ohmeter to check continuity of the switch?
Just another thing for you to check.

 

[Dan_68]

Funny enough i havnt tested that because all buttons stop working after a bit but i will.

 

[Dan_68]

tested thw switches its not them. when i plug the control board the green one in its lowering the standy voltage

 

[Dan_68]

ohk. so maybe some can help from the basics. what is rl om and vs on. the va and vs voltage. one of the large ceramic resisotra gets really got when the green board is plugged in but not to bad when its not

 

[davenn]

ok Dan,

how about a close up pic of each board nice and sharp and well lit so we can easily read component values etc
then we all can have a look and see if there's anything obvious that you may have overlooked, there's a few experienced eye's on this forum lol

in the mean time, measure the voltage across that heating up resistor and tell us what it reads
what is the value on the resistor? can you tell which voltage rail that resistor is on 5V, 12V something else ?
its its really heating up excessively it infers that something further down that line is drawing a lot of current

Dave

 

[Dan_68]

Both resisgltors are in series but the second one has the full 13v drop across it. It connects to a transistor but i have checkee that. Its on the vs or va.rail what ever that means

 

[Dan_68]

I have taken some photos, not brilliant. but you gurus might know still. I have trouble tracing voltages lines when it steps across diodes and capacitor.
Thanks

 

[sheldonstv]

make and model and ill post the manual for the set.....

 

[Dan_68]

maxess MP32T, thanks

 

[Dan_68]

Any one have any ideas of tracing the fault. How can i tell if the fault is in the green board or the power board. I need to know how to trace it to fix many of thins.

 

[davenn]

we really need the service manual to see the circuit diag.

just still waiting to see sheldonstv has the manual and will post it

D

 

[Dan_68]

Hi all, i am still working on this and i have traced it down to the 5v low drop regulator just a the end of the circuit. When the board is plugged it this is where the voltage drop is happening. Now i have realised my stnadby voltage is ok but the board has 5Vsc, whats sc stand for. Its a 4 pin IC (Vin,Vout,Gnd,Control) when the tv is turned on the Control pin rises to 5v then back to 0 and nothing else. The Vin stays at 5v if other board is plugged in or not and Vout is 5V with other board unplugged and 2.8v plugged in. Any ideas here bad IC or something else happening

 

[Dan_68]

Hi all im got the tv back out for another go. what i have is 5v supply to the av board but when the AV board is plugged in my voltage drops. Now this must be because of a short on the power board. Any ideas of how to trace back to where the short is.

 

[hattonhall]

Hi Dan.........did you end up fixing this? I hope so!

If you did not........do you have the remote........mine is Kaput!

If you do, please email me at:-
[email protected]

cheers mate.

hattonhall

 

[hattonhall]

Why they remove the email beats me........please ring me on 0432-990-373
hattonhall


let's see if they remove my phone number!