Lg 42pj550

[Blueaardvark46]

Turns on fine with good sound but no picture. All voltages are present and
correct and it seems that the Y and Z boards are doing their job because
the heatsinks are getting warm. The curious thing is that there's a LED flashing
on the LVDS board with a sequence of two short flashes, then a longer one, then another short one, then a very long one. This keeps on repeating and it
looks like a fault code. Any ideas?

Thanks
John

[sordids999]

Re: Lg 42pj550

Test patterns from control board to eliminate main board ok ?

[vinceroger69]

Re: Lg 42pj550

not sure what chassis your tv uses it may say on a sticker? but this maybe the service manual link
https://servlib.com/lg/tv/42pj550-zd-chassis-pd01a.html

[Blueaardvark46]

Re: Lg 42pj550

The manual says to look for a waveform on P1004 but I can't see this test point.

[vinceroger69]

Re: Lg 42pj550

does that manual match the tv chassis number if not maybe why you cant find the test point try running the test patterns if it dosnt say how too in the manual search this forum theirs a few threads on how too run them on lgs

[dick_barton]

Re: Lg 42pj550

Hi John, Can you post photo's of your circuit boards and how they interconnect?

[dick_barton]

Re: Lg 42pj550

Disconnect the ribbon cable between the mainboard and logic board and short the two pads marked Auto Gen on the logic board. Power up and you should see test patterns displayed on the screen.

[Blueaardvark46]

Re: Lg 42pj550

No still no raster or test pattern. Here's some pics of the boards.

[Blueaardvark46]

Re: Lg 42pj550

Here's the pics this time!

[dick_barton]

Re: Lg 42pj550

OK so you need to measure and give the readings taken of Va, Vs, M5V, 17V, STB5V, 5V, Vz, +15VF, +5VF, VSC etc voltages along with all the others highlighted on the circuit boards. Possible logic board fault.

[Blueaardvark46]

Re: Lg 42pj550

Ok here's the measured voltages:-
Va = 58.9v
Vs = 202v
M5v = 5.0
17v = 16.7
STDBY5 = 5.0
+5VF varies between 8 and 12v
+15F varies between 17 and 25v
SUSON varies between 3.6 and 6.5v
These variations occur when the picture brightness alters. ( I had scarted the
picture out to another set just to check the video processing)
I also noticed that where there are high voltage warnings on the 5 screw connections between the Y board and the buffer board there was only 45v on
the bottom screw and barely 8v on the other 4. Surely this should be higher?

[dick_barton]

Re: Lg 42pj550

Va, Vs M5V and 17V supplies all look good. However it looks as thought the voltages on the Ysus board are fluctuating.
On the Ysus board measure Vsc which you measure between the two points marked and also measure the +15V point

Unfortunately your photo's are very blurred so I'm not sure what you mean about the screws. All screws should be firmly screwed down but not overtightened so as to crack the pcb.

[dick_barton]

Re: Lg 42pj550

The +15VF and +5VF I believe should be measured with respect to Floating Ground (ie black meter lead connected to Floating Ground) which should be marked on the board.

[Andrew F. Ali]

Re: Lg 42pj550

Y-SUS Bd. not generating a proper 5V for the Logic Bd. to function. Yes I will say the issue is on the Y-SUS Bd.

[Josecarioca]

Re: Lg 42pj550

Debes medir las 2 Resistencias de 22 Ohm 5W situadas en la parte superior de la fuente de alimentacion, cuando alguna de ellas está abierta o su valor no es correcto presenta fallo de Stby o parpadeo de LED.