LG 50PK550 Intermittant Clicking (works sometimes)

[mostachio]

Hi Badcaps! I need help please I'd like to fix the above tv.

I've read lots and lots of info, but please dumb down a lot of stuff for me, I take adequate precautions but i'm still learning as a hobby.

Symptoms:
Turn on - immediate reclick of power board trying to fire it up
Leave it for 45 seconds - it will work, full display, sound everything.
Leave it a further 15 minutes - It will turn itself off and start clicking again.

I assume this is a power board problem, there is no visible doming of caps, or any problems I can see. I've read that it may be a problem with AC DETECT signal (there are 5 octocouplers on the reverse) or a specific resistor.

I have ohm tested all fuses and all ok. I have not yet tested any output from the power board. Be great if I could have some help isolating this! I have an isolating transformer, digital multimeter, soldering station and many spare components / whole boards I can pull bits from (and a 'radio shack' type store to get the ones I don't)

Please let me know if you'd like any pics or vids
thank you

[Hamie]

Re: LG 50PK550 Intermittant Clicking (works sometimes)

First of all you need to make sure what board is causing your fault.
Most of the boards can cause your symptom.

Unplug the y and z boards from the power supply and monitor the vs and va voltages. See if they drop, or if the power supply continues to cycle.

[mostachio]

Re: LG 50PK550 Intermittant Clicking (works sometimes)

Hi Hamie, thx for your reply.

Here are the voltages:
(Without Y & Z unplugged)
VS Voltage = 202V on the 2 points on the Y board and on the point Z board connectors
VA Voltage = 59V on the two points on the Y board connector

(With Y & Z Unplugged)
TV no longer hums, barely audible ticking from power board (appears to be tf)
VS & VA Voltages remain the same

No voltage varies, and I can't test on the cycle anymore as it is now intermittent cycling :/, did not power cycle with either board unplugged (both & one at a time) and does not do it with both plugged... today. I'm running through a full movie through the HDMI at the moment to see if I can get it to again.

EDIT: Almost through whole movie, no cycle. I've tried to manually start it cycling but no success. I think it a hazard to leave it on all night to stress test but it does not appear to show fault now... I guess this makes testing a lot harder without being able to reproduce the fault.

[mostachio]

Re: LG 50PK550 Intermittant Clicking (works sometimes)

I could no longer edit, but update!

Halfway through the second movie, after it had warmed up, it started cycling again. VA & VS Voltages at 0 (every one) and do not fluctuate, either with Y & Z boards plugged or unplugged.

[Hamie]

Re: LG 50PK550 Intermittant Clicking (works sometimes)

Possibly has a cold/broken solder connection on the power supply.
Can you upload some photos of the underside of the power supply.
Photos have to be clear.

Take maybe 4 photos and label them 'top left' top right' 'bottom left' etc.

[mostachio]

Re: LG 50PK550 Intermittant Clicking (works sometimes)

That would make sense... I am able to re-flow the back of the board if needed.

Here are the pics of the rear of the power board etc and some further information, the back of the board was a little dusty, tried to get most of this off.

Panel P/N: PDP50R10100
LGIT PCB P/N: 3PAGC10016A-R
PCB: EAX61392501/10
PSU P/N: EAY60968801
Rev 1.3

I cannot attach IMGs, the popup is not coming up. I have shared a folder on google drive. Link:

http://tinyurl.com/q5dohjm

I have also found this badcaps thread of same model & panel https://www.badcaps.net/forum/showthread.php?t=34420 (i cannot hyperlink either..) with exactly the same problem. No further updates though to whether he fixed it or performed the alignment though.

[Hamie]

Re: LG 50PK550 Intermittant Clicking (works sometimes)

Well nothing is jumping out at me.
Usually coils, transformers and anything attached to a heat sink can sometimes suffer from bad solder.

This is a common fault with this board that involves the 2 wire wound (22ohm I think) resistors located top right of your board, look like white blocks.

But your fault is completely different form the fault that they usually cause.

You can check them in circuit they will be either 22ohm or 11ohm if they are in parallel.

[mostachio]

Re: LG 50PK550 Intermittant Clicking (works sometimes)

No worries, thanks for your help anyway.

The top 3 white resistors are RWS-5W 10R0JSMT and all three measure at 10.5~ohm +- .1

Short of buying a new power board just yet I think I might go over all of the rear solder points except the smd stuff and try that aligning method with the VR's for VA & VS (as they are both a tiny bit undervolting the panel. Panel voltages being 203 VS and 60 VA). I figure 204 and 61 to completely rule out any undervolting issues (pulling at strings a little here).

Will keep updated if I get it going (even if I have to buy a new board). Cheers

[Hamie]

Re: LG 50PK550 Intermittant Clicking (works sometimes)




Found a more likely cause for your fault.
The description describes your fault almost perfectly.

Get a hair dryer and aim some heat at this chip and see if your fault occurs faster than usual.

[mostachio]

Re: LG 50PK550 Intermittant Clicking (works sometimes)

I'll give that a go. Despite it being <10C here (New Zealand) the fault occurred almost instantly this morning so is really intermittent (compared to the 3hrs~ the other day) so I can't really say for certain whether or not the IC caused the drop most times while testing...

I have adjusted VS & VA to 204 and 61 to no effect, have not done any solder joints yet. But I wonder if heat.. is causing bad solder joints to open on that IC vs a faulting IC. I'll go over the solder for IC & rear of board anyway while i'll i'm waiting for some stability to test with heat gun on very very low heat.

Thanks

Edit: I actually don't have that exact IC on rev 1.3 board, I have

V1_1A-1A83
F431SMSF11
1011 KOREA

Ok, so resoldered IC, Transformers, Transistors, Resistors (double would white ones), and any potentially suspect joints I could see. I also checked ohm rating on the other white double wound resistors and found:

Two identical resistors : MPR-5W R030JSMT , in parallel have different ohmage ratings and far different than identical resistors on the board.

And I have to just double check I'm checking ohmage right. I have it set too 200 in the ohms scale on my multimeter (200, 2k, 20k, 200k, 200M). The same resistors at other points in the board measure 0.5 which I assume 5ohm. These resistors in parallel measure:

R607 - 65ohm
R613 - 50ohm (or 5.~ on multimeter)

(and now they're back to 0.5 without any change in what I did )... Don't know if I just picked up a fault there or not... Resoldered their joints and am about to re-test.

Fail. I can hear it reclicking in the lounge after about 1 minute.

[mostachio]

Re: LG 50PK550 Intermittant Clicking (works sometimes)

Update: Testing all diodes for wrong way continuity *uh hope that makes sense* and found diode D304 to be a completely open both ways (this is testing on board).... I'm going to de-solder this and re-test but I think i've found the/a problem... No is fine off the board, bad logic on my part. reading 188 and non-continuity. Have put back. Funny how this was the only diode to show a short back the the other way on board though... The three items that separate this connection are a resistor, that diode and a smd cap on the rear of the board. The Resistor beside it (Orange, blue, silver, gold, black) i've used a colour calculator to find out the ohmage (0.36 O), it tests at 8 O.. (or 0.8 on the 200 setting on my multimeter)

[mostachio]

Re: LG 50PK550 Intermittant Clicking (works sometimes)

Update FIXED: D304 open both ways led me to finding IC301 regulator to be faulty. Replaced IC301 (3BR1565JF Regulator) & for the hell of it D304 diode and fault gone. Thanks for all the help

[mostachio]

Re: LG 50PK550 Intermittant Clicking (works sometimes)

Scratch that it faulted again. 3 months continuous good usage though. I've ordered another IC301 (3BR1565JF) but any idea why it could be doing this? I added good quality thermal grease with installation etc...

[lesjones]

Re: LG 50PK550 Intermittant Clicking (works sometimes)

Let me know if that fixed it again. I have one that has the same problem. Thx!

[mostachio]

Re: LG 50PK550 Intermittant Clicking (works sometimes)

Will do, the ebay seller replaced it free of charge and i bought from a 'reputable' firm too just in case there's some kind of quality issue with them. Will use the latter first lol. Great tv though

[mostachio]

Re: LG 50PK550 Intermittant Clicking (works sometimes)

Nope, not fixed... maybe it was the diode? will replace and update again, all the white resistors still test ok. Apart from that I'm at a loss as it was fixed for a long period and now.. while still going, after a short while it'll power cycle then again, then continually click. Let you know how replacing diode goes.. don't really want to fork out for a new power board..

[mostachio]

Re: LG 50PK550 Intermittant Clicking (works sometimes)

Tried replacing both the diode D304 (SR104 , 40V, 1A, 30surge A schottky) & the IC301 rectifier again but no go (still same issue). Ohm tested the 3 white ceramic resistors again and they are all fine 10.5-11.1ohms on and off the board. Not sure what to do now except buy a new power board as I can't test the chip mentioned it doesn't stay on long before prior to clicking... and have reached about the extent of my electronics knowledge lol. Thanks anyway

[seraph]

Re: LG 50PK550 Intermittant Clicking (works sometimes)

Hi I have a similar problem with my set, trying to diagnose before I order more parts!

If I turn it on after being unplugged for a while it'll power up for at most 20 seconds, sometime enough to see the no signal text on screen, but then it clicks off and only click the relays when trying to turn on. Same 3 clicks when everything is disconnected except the ac to psu.I Have checked the 3 10 ohm ceramic resistors and theyre fine, D304 is fine off board, f302 is fine. Does ic301 always take out d304 and f302 when it goes??

Caps all look fine (unsure how to test) all other ceramic resistors read fine.

Anything else commonly go wrong on these boards?

[sordids999]

Re: LG 50PK550 Intermittant Clicking (works sometimes)

Possible fault:
All supply voltages will come up then die
Intermittent going on and off and clicking
will work for 20 mins then will go off and start clicking


If heating/cooling ic701 makes no difference

check R103,R104,R105,R106,R107,R108,R109,R110,R111,R112,R113

hope this may help

[seraph]

Re: LG 50PK550 Intermittant Clicking (works sometimes)

Do you happen to know what the values are off the top of your head? I cant read them..