LG 42PC55 Plasma

[Wilz]

Hello everybody! : )

This is my first plasma TV (I have fixed bunch of LCD screens) so this is completely new to me.
So here's the problem: when click power button TV tries to start (relay clicks), but after few seconds I hear a brief buzz somewhere around PSU-board and TV goes back to standby.
I have measured ac-det -pin, as suggested here in another LG plasma topic, it reads 4,7V in standby, when starting it jupms to about 5,1V and after that back to 4,7V. Vs-line jumps to about 1V during that brief buzzing sound. Caps seem to be OK.

Things I have already tried:
-Unplugging signal cable from YSUS: no effect
-Unplugging ZSUS power: no effect
-Unpluggin ZSUS power AND YSUS signal cable: TV stays on and gives ~190V to Vs-line.

So please, how do I get this working again? : )

(Sorry for my bad english, I hope you understand)

[laszlo31]

Re: LG 42PC55 Plasma

Hi,

I'm sure you came across my thread when you checked the forum:
https://www.badcaps.net/forum/showthread.php?t=22017
I guess I have the bigger brother of your TV, the 50PC55 but with same issue that might be related to the activation of PSU protection mode (stays in stand-by).
Check my thread, unfortunately I am also investigating as the TV still not fixed but you might see some similarities. Few tips:
- Did you check all capacitors for bulging or leakage?
- Did you measure all fuses, including SMD fuses?
- Any sign of cold joints, burnt or discoloured components?
Good luck.
P.S. Fill out your country and voltage in your country under your registration before the veterans jump all over you ;-)

[Wilz]

Re: LG 42PC55 Plasma

Yes, the caps were the first thing I inspected, but they at least look OK (no bulging or leaking), no burned looking components either. I also measured all the fuses I could find, the were fine too. Removed PSU and re-soldered about 30 suspicious looking joints but still nothing.
Just measured Y- ands ZSUS board power inputs against ground, not shorted atleast.

If you need pics from some spesific location I can take them. : )

[selldoor]

Re: LG 42PC55 Plasma

With it all connected up can you test the voltages out at the power supply
connectors - post as follows
Connector XX
Pin Name Actual
1 12v 12.01
2 12v 12.01
3 5v 4.82
4 ps-on 2.2 and so on

[Wilz]

Re: LG 42PC55 Plasma

So heres the voltages, first pin number, then standby voltage, then voltage when trying to start.

Connector P12

1 5V: 0V - 5,0V
2 GND
3 Vo (60V): 0V - Changing from 0,4V to 0,9V whan trying to start
4 GND
5 GND
6 GND
7 NC
8 Vs (190V): 0,51V - 0,8V
9 Vs (190V): 0,51V - 0,8V

Connector P2

1 19V: 0V - 18,9V
2 19V: 0V - 18,9V
3 GND
4 GND
5 6V: 0,16V - 6,0V
6 GND
7 3,4V: 0V - 3,4V
8 GND
9 12V: 0,17V - 11,7V
10 GND

Connector P1

1 AC-DET: 4,75V - 4,9V
2 RL ON: 0,02V - 4,9V
3 STB 5V: 5,1V - 4,9V
4 GND
5 VS ON: 0,02V - 4,9V
6 5V DET: 0V - 4,9V
7 M5V-ON: 0,03V -5,0V
8 STB 5V: 5,1V - 4,9V
9 GND
10 NC
11 6V: 0,16V - 6,0V
12 GND
13 3,4V-ON 0,02V - 4,9V

[selldoor]

Re: LG 42PC55 Plasma

Can you get a clearer picture of the ysus. On the zsus I cant see any fuses but there are a number of components designated FLxx these are fusible links and act like fuses - can you test them as such. Use ohms scale and state result. On the left hand side there is a cap that looks like the top is split? is it or is it just the picture?

[Wilz]

Re: LG 42PC55 Plasma

Here's maybe a bit better picture of YSUS.
Cheched all FL-fuses, they seem to be OK. That's hot glue on top one of the caps, not splitted.

[selldoor]

Re: LG 42PC55 Plasma

Ok on the ysus there are 5 fuses and some FLs can you test them all and please list the results
Fxx ?? Ohms
Fxy ?? Ohms and so on- showing numerical values - (do not rely on continuity test beep.)

[Wilz]

Re: LG 42PC55 Plasma

FS1: 0,3ohm
FS2: 0,3ohm
FS3: 0,3ohm
FS4: 0,3ohm
FS5: 0,3ohm

FL1: 0,3ohm
FL2: 0,3ohm
FL3: 0,3ohm
FL4: 0,3ohm
FL5: 0,3ohm
FL6: 0,3ohm

Multimeter leads shorted: 0,2ohm so the all are about 0,1ohm.

[selldoor]

Re: LG 42PC55 Plasma

They are all good then - Ive got nothing- I assume you are watching laszlo's thread and trying anything that comes up on there.