urgent help 50pk550-so desperate here

[ramirachamim]

hello everyone.
this is my first post here so i would like to express my deepest gratitude for all of you-absolutely saints!
as mentioned, i am so desperate,mad,sad whatever you choose
could really use your help here...
i own this plasma tv set LG 50pk550 and the problem description is as follows:
as i plug the power cord, red stby lights up perminant.
when trying to fire up(via remote or touch buttons) two fast relay clicks followed by stby light turns off.
after about 8 seconds, another click followed by red stby on again.
through out all mentioned process the screen stayed solid black(verified in complete darkness)
destructive googling lead to:
1.bought the damn "repair kit" which included voltage regulator and couple of high white corner resistors-replaced everything with no change.
2.executed different voltage examination-seems to be ok.
3.executed two light bulbs load test-lights worked and stayd on(psu ok right?)
4.executed sync board( the one with flashing tiny green led) test by jumping two holes as said in the training manual(for 50pk750)-nothing appears on the screen at all and it is still solid black, not even a clue for backlight.
5.i must mention that when power on button pressed (stby light off), the y and Z boards makes a silent "buzz" noise, as if it works ok( i guess ).
6.checked ALL visible fuses within ALL boards-continuity OK.
7.i must also mention that all caps and boards seems to be BRAND NEW as can be seen whitin attached photos.

PLEASE any more ideas,directions,examinations?
have all needed tools(solder iron,multimeter,solder iron pump etc...).
thank you very much in advanced,
rami.

[Hamie]

Re: urgent help 50pk550-so desperate here

In the top corner of the y-sustain you'll find 2 resistors marked vsc and -vy.

Measure across these resistors and see what voltage you get.

-Vy should be around -180v
Vsc should be around 150v

[ramirachamim]

Re: urgent help 50pk550-so desperate here

thanks so much for your affort!
will do in 2 minutes.

[ramirachamim]

Re: urgent help 50pk550-so desperate here

if you meant the resistors in attached photo:
vsc=15.3 Vdc
vy=14.3 Vdc
could not locate -vy doe.

[ramirachamim]

Re: urgent help 50pk550-so desperate here

attached photo.

[Hamie]

Re: urgent help 50pk550-so desperate here

OK now unplug the buffers and check them again.

[ramirachamim]

Re: urgent help 50pk550-so desperate here

1 min plz

[ramirachamim]

Re: urgent help 50pk550-so desperate here

ok
vsc= about -0.8 vdc
vy= about -1.0 vdc

[Hamie]

Re: urgent help 50pk550-so desperate here

Doubt that can be right.
Have you completly removed the buffers?

[ramirachamim]

Re: urgent help 50pk550-so desperate here

like so?

[Hamie]

Re: urgent help 50pk550-so desperate here

No they are still screwed in.
For the avoidance of doubt just completely take them out.

You can still leave the orange panel ribbons attached but flop the buffers out of the tv so they nolonger make any connection to the y-sus.

The buffers cannot touch the ysus in anyway.

[ramirachamim]

Re: urgent help 50pk550-so desperate here

ok,sry for the delay,demanded some heavy unscrewing...
vsc=-0.6
vy=-1.0
examined as shown

[Hamie]

Re: urgent help 50pk550-so desperate here

OK leave the buffers out for now and check the voltage for VZB on the z-sustain.

[Hamie]

Re: urgent help 50pk550-so desperate here

To clarify, when checking VZB have the y-sustain unplugged form the SMPS

[Alastair E]

Re: urgent help 50pk550-so desperate here

Short IGBT's on y-sus most likely.

Check Vs line for short on y. and x

[ramirachamim]

Re: urgent help 50pk550-so desperate here

To clarify, when checking VZB have the y-sustain unplugged form the SMPS

hi hamie,
please do include all of "well knowns" or "clarifications" up front.
if you wouldnt clarify i would never unplugged the y sus myself.
now for the practical issue:
unplugged the y-sus.
the z board had 2 capacitors says "VZB"
both reads zero 0 VDC.
photo attached.

[ramirachamim]

Re: urgent help 50pk550-so desperate here

sry resistors of course.

[Hamie]

Re: urgent help 50pk550-so desperate here

One marked <VZB> isn't a test point it's to label the VZB potentiometer.

The VZB test points are marked - and +

You need to.put your meter in DC volts put your negative probe on the - point and positive on the +

Is the tv on when your doing these tests? Because it's strange that both the y and z to go faulty at the same time in this model as they are not linked directly.

[Nick's Tvs]

Re: urgent help 50pk550-so desperate here

Shot in the dark here from my experience with these but the logic board tends to cause the symptoms you are seeing. In your original post under step #4 you mentioned a tiny flashing green light. Are you repeating a blog post or are you actually able to see the light flash on the board?
Also Alastair E mentioned earlier that it could be blown transistors on the sustain board. A quick way to check it would be to go in ohms mode with your meter and measure the resistance between the VS line and the chassis ground on both your Y and Z susatins. Now that doesn't allways work as you can have shorts on the board that won't reflect on the vs line. If you do get a short on one of them, then you know where to go from here, if you don't, then you may want to double check by taking ohm readings on all the transistors that are screwed into the heat sinks.
If you have any questions on taking those measurements, please let me know.

[ramirachamim]

Re: urgent help 50pk550-so desperate here

One marked <VZB> isn't a test point it's to label the VZB potentiometer.

The VZB test points are marked - and +

You need to.put your meter in DC volts put your negative probe on the - point and positive on the +

Is the tv on when your doing these tests? Because it's strange that both the y and z to go faulty at the same time in this model as they are not linked directly.

hi hamie,
got it
checked the "-" and "+" with my dmm on dc volts.
it reads about 3 vdc on stby and 204 vdc when "on"
regarding your question the set was on when executed the tests for the y brd.
nick- first of all thank you for your help, really appreciated.
all i wrote at my first post was REAL.
didnt quated nothing...
you guys probably figured out by now that my knowledge is near to zero...
however i can executed any examination if guided step by step..
please detail how do i examine for bad resistors.
any explination attached to photos would be great.