LG 50PJ550 clicking on/off

[maastermind]

Hi all,

New member here, trying to fix my parents' TV. It is an LG 50PJ550 plasma manufactured in 2010. Last night they were watching TV and heard a POP, then the TV wouldn't stay turned on anymore. I have been looking for a fix online for most of the day but I still cannot determine what is wrong.

SYMPTOM: Power cable plugged in, get the red light on in the front. Turn TV on, red light disappears, hear it click-click, no flash or anything on the screen, red light appears again, hear it click-click. Same thing happens each time.

So far I have done the following:

1) I have checked the power supply board with a multimeter. My findings are indicated in the second picture.

2) I have checked the YSUS and ZSUS boards with a multimeter. My findings are indicated in the third and fourth pictures.

3) I have visually checked all the capacitors and have found none that are blown or bulging.

4) I unplugged the YSUS cable from the power supply board and turned the TV on. The TV stays ON now but nothing else happens.

5) I plugged the YSUS cable back onto the power supply board and I unplugged the ZSUS cable from the YSUS board. I turned the TV back on and my symptom happens again with the addition of a humming sound for 2-3 seconds on startup and another 2-3 seconds when shutting down.

I don't know what my next step should be, I would greatly appreciate any sort of help on this one.

Thanks in advance!
John

[Agent24]

Re: LG 50PJ550 clicking on/off

If it runs with the YSUS unplugged I guess that indicates a fault on that board. First thing I would do is check all the big power transistors\diodes etc on it for shorts.

[Hamie]

Re: LG 50PJ550 clicking on/off

Everything on the ysus heatsinks need to be checked for shorts.

Usually the black heatsink is ok.

Start with the smallest silver heatsink. There should be a diode RD2003, and 2 igbts. If they test short then both IGBTS will need to be replaced.

Then check the larger silver heatsink usually most of the parts on this are blown.

btw the ysus can usually take out the zsus when it fails, so you'll need to check the heatsinks for shorts.

[maastermind]

Re: LG 50PJ550 clicking on/off

Thanks for the replies, I will check for shorts, is there any easy way to do this?

[Hamie]

Re: LG 50PJ550 clicking on/off

Do you have a digital multimeter?

[Andrew F. Ali]

Re: LG 50PJ550 clicking on/off

Testing the Y-SUS Board you must first disconnect as follows:
1. P211: Connector Y-SUS to Z Drive P2
2. P210: Connector Y-SUS to SMPS P813
3. P212: Connector Y-SUS to Y-Drive Board P205
4. P101: Connector Y-SUS to Control Board P101
Next with your DMM on the DIODE CHECK connect the BLACK lead on the chassis (bare metal frame)
With the RED lead on P211 Diode Check should give the following:
Pin 1-2: Gnd (0)
Pin3: n/c
Pin 4-5: Open (1)
Pin 6: n/c
Pin 7-11: Open (1)

With the RED lead on P210 Diode Check should give the following:
Pin1-2: Open (1)
Pin3: n/c
Pin4-5: Gnd (0)
Pin 6-7: Open (1)
Pin 8: Gnd (0)
Pin 9-10: 1.5

[maastermind]

Re: LG 50PJ550 clicking on/off

I do have a digital multimeter and I will follow Andrew's test and report back. Thanks!

[maastermind]

Re: LG 50PJ550 clicking on/off

I cannot for the life of me release the P212 and P101 ribbon cables! I checked Youtube but they only showed a different style of ribbon cables. Please help!

[Agent24]

Re: LG 50PJ550 clicking on/off

FFC (flat flex cable) connectors usually have a latch that flips up or slides out, but if there is no such latching mechanism, it's probably the type that the cable just pushes into. In which case you just have to pull it out, go carefully. You shouldn't have to pull very hard.

Sometimes the other end of the cable is attached with a latching type, it might be easier to undo the other end.

And sometimes (but not usually for FFC), the cable is actually soldered into the board and what looks like a connector is just some kind of rigid housing to make it easier to insert into the board before soldering. Unlikely to be the case here, though.

[maastermind]

Re: LG 50PJ550 clicking on/off

Thanks for the help Agent24! Sorry for lacking a picture but it was the type where you just pull it out.

Anyway here is what I found on P210 and P211 using the CHECK DIODE function on the multimeter. I placed the ground in one of the screw holes for wall mounting and confirmed it was a good ground before continuing.

P210 (looking at connector, top to bottom)
+5: 800
+5: 500
GND: 000
+VA: 1
+VA: 1
GND: 000
GND: 000
+VS: 072
+VS: 072

P211 (looking at connector, left to right)
SER: 408
SER: 408
SER: 408
SER: 408
SER: 408
SER: 408
NC: 1
+VS: 072
+VS: 072
NC: 1
GND: 000
GND: 000

I hope I was checking the right connectors because in Andrew's post there is supposed to be 10 and 11 pins (P210 and P211), I had 9 and 12, respectively.

[maastermind]

Re: LG 50PJ550 clicking on/off

I haven't had the opportunity to check for shorts that Hamie described in his post yet, would I still need to do that after checking for shorts on P210 and P211? What do the readings mean? Is something shorted? Thanks

[Agent24]

Re: LG 50PJ550 clicking on/off

I have no idea what the readings on P210 and P211 mean as I have not seen a schematic etc. Hopefully Hamie can tell you.

It might be useful to check the other points mentioned anyway though just in case the differences in pin numbering mean the readings from P210\211 are not clear.

[Hamie]

Re: LG 50PJ550 clicking on/off

These are the parts that are usually faulty and need to b checked.

D01 - RD2003
Q02 and Q03 - 30F124

Q29 - K3667
Q26 and Q27 - fqpf51n25

Q22 and Q24 - rjp63f3

D21 - rd2004

Usually D01 and D21 will test ok, if they are also shorted then you will need some extra parts.

Also remove the glue between the legs of All blue disc ceramic capacitors, eg: c203.

Once repaired the capacitors still might blow off the board so make sure you have 2 or 3, 102k caps just in case.