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slappala replied to LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

in Troubleshooting TVs and Video Sources

03-13-2018, 12:45 PM
Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

Hi,
It's been a Long time from my last post, but I will let you know that the optocoupler mod has worked to this day , so about 6 years. TV is still working.

Today I got one black horizontal line in the middle of the tv screen and also I have some red dots on black backgrounds sometimes.

I think this tv is going to the recycling plant now. Tried to fiddle with the ribbon cables but no help for the black line.

Happy to hear the optocoupler mod has helped others too.

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slappala replied to LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

in Troubleshooting TVs and Video Sources

03-10-2012, 07:14 AM
Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

I guess U702 monitors the AC primary's two sides with these optocouplers.

When the 3-4 pins are joined the U702 thinks the AC is on all the time by circulating the 5.v signal back to the IC. Basically thinks the opto is on state what it really is also except during the 200ms at the start where the opto ON signal would be lost sometimes.

Yep, something wrong with the optos or the AC primary waveform at the start..TV works now again without hickups so before some PSU components...

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slappala replied to LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

in Troubleshooting TVs and Video Sources

03-09-2012, 12:04 PM
Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

I checked the datasheet again and tried it out. shorting these 3-4 pins on those 2 optocouplers help and gets the tv going when it's clicking.

phew..

I just don't know what could cause this..and frankly don't care .

I measured the signals on both sides of the opto transistor and voltage's drop out for some reason when clicking..

The scope waveform to the opto led side changes when this happens (dirtyer, but peak to peak just a hint)
AC voltages don't...

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Last edited by slappala; 03-09-2012, 12:17 PM.
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slappala replied to LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

in Troubleshooting TVs and Video Sources

03-08-2012, 10:44 PM
Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

sorry about that, I will change the pics to attachments. I tought it was best to sent these as links.

parts are NEC 2571 / SJ605, not included in the repairmanual BOM.

Might take 1h or so to delete the files from imageshack(Said when deleting the links.)...

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Last edited by slappala; 03-08-2012, 10:56 PM.
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slappala replied to LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

in Troubleshooting TVs and Video Sources

03-08-2012, 02:56 PM
Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

Powered by Nokia N8

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slappala replied to LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

in Troubleshooting TVs and Video Sources

03-08-2012, 02:53 PM
Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

[URL="http://*************/g/9/201203081821.jpg/"]http://*************/g/9/201203081821.jpg/[/URL]

There they are in imageshack, let me know if you can see the pics or not.Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

[URL="http://*************/g/9/201203081821.jpg/"]http://*************/g/9/201203081821.jpg/[/URL]

There they are in imageshack, let me know if you can see the pics or not.Re: LG 42PC3RA SMPS power_ysus problems on/off/on

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slappala replied to LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

in Troubleshooting TVs and Video Sources

03-08-2012, 02:39 PM
Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

Yep,
when the 5.v gets pulled straight from stby line it still deactivates 3.4v feed to the main board...

Maybe that's why it start's on the second try. I will post pics. My board is different. I did not see optocouplers at fast look :/.

Also I don't have schematics since it's PC3ra version and service manual does not include them.

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slappala replied to LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

in Troubleshooting TVs and Video Sources

03-08-2012, 12:28 PM
Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

I bypassed the AC detect and hooked it to a constant standby 5.v line. It works now, but the set starts twice quickly. Second time it stays on.
I would need a 5.v clean constant signal from some point. Where did you take it?

Also the line I used is really messy on my scope. not a clean 5.v I would say..and has a 0.5v spike that could cause the second start attempt/reset.

I think the PSU control chip might take the AC detect line down in case of the voltages don't rise enough quick....

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Last edited by slappala; 03-08-2012, 12:31 PM.
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slappala replied to LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

in Troubleshooting TVs and Video Sources

03-08-2012, 11:51 AM
Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

Hi, yep.
I think the reason is the powersupply can't get the voltage ramped up upon start enought quick--> mainboard shuts down the powersupply board.

Maybe this is the reason some tv:s have had software update..to wait some time for ramping up the voltages in older PSU:s..

AC detect is I think 5.v signal that comes when the secondary side is switched on. I think that works for my set as I have measured it before. Off course goes to zero after some MC forces the PSU down because...

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Last edited by slappala; 03-08-2012, 11:57 AM.
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slappala replied to LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

in Troubleshooting TVs and Video Sources

03-08-2012, 10:51 AM
Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

had it off the mains for 1/2h and now it started fine again..it was sitting on teh mains for 3 days after a long period of the mains..

somehow this is connected to plugging the unit in.
If I take off the mains cord when not watching I'll bet it works. What is causing this? something on the PSU primary side??

Or some software reset thing on main cpu(control cpu:s...

Any help will be appreciated

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slappala replied to LG 42PC1D plasma - clicking repeatedly

in Troubleshooting TVs and Video Sources

03-08-2012, 10:06 AM
Re: LG 42PC1D plasma - clicking repeatedly

Ok, today the same symptoms appeared again.. :/
It's freaking wierd. maybe I'll try to bypass the AC detection..

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slappala replied to LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

in Troubleshooting TVs and Video Sources

03-08-2012, 10:06 AM
Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

Ok, today the same symptoms appeared again.. :/
It's freaking wierd. maybe I'll try to bypass the AC detection..

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slappala replied to LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

in Troubleshooting TVs and Video Sources

03-06-2012, 02:40 PM
Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

after 4h looks to be a ok..on/off working normally also even when hot.
Have to use it for a while to call it done.

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slappala replied to LG 42PC1D plasma - clicking repeatedly

in Troubleshooting TVs and Video Sources

03-06-2012, 12:35 PM
Re: LG 42PC1D plasma - clicking repeatedly

I changed the y-sus board STK chip and it looks to be working now with the protection circuit still intact with less red sparks.

Still testing for durability this week before saying it's fixed for now.

STK chip was about 20$ from ebay..

I have tested a lot of the caps and I see bigger ESR readings with my meter and I think the high voltage caps have bigger ESR values than you might think..check the specs from datasheets.

See my thread for changing the STK chip if you go that ...

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slappala replied to LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

in Troubleshooting TVs and Video Sources

03-06-2012, 11:58 AM
Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

Finally watching/repairing the tv again. I still did not manage to get nice amp clamp.

I bit the bullet and bought 2 new STK chips..changed the Y-sus board STK chip and have been testing it for few hours now..no problems yet.

Cross my fingers...and thumbs..next weeks will show it I guess..

VA and VS are turned down for now..I don't have back protection on the tv if It still gives me some !§$&%/&(..

power slopes at VS and VA look consistent when powering...

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slappala replied to LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

in Troubleshooting TVs and Video Sources

01-19-2012, 08:04 PM
Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

I got the amp meter..used..was broken. waiting for new one to isolate the problem to y-sus board IC

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slappala replied to LG 42PC1D plasma - clicking repeatedly

in Troubleshooting TVs and Video Sources

01-19-2012, 07:59 PM
Re: LG 42PC1D plasma - clicking repeatedly

I bought amp meter few weeks/ a month ago to get better idea of the situation.
Chassis ground had some AC in it to back up the conclusion of y-sus or z-sus board leaking some current in start-up situation. (Not the caps)

The amp meter was faulty so I'm waiting the new one to arrive to be sure.

A/C detection is not there for fun..it's for safety also. That 's why I did not by pass the protection scircuit..(plus the dots)

measure the chassis voltage levels DC and AC againts ground when starting...

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slappala replied to Lg 42" plasma model p2pc3d-ud

in Troubleshooting TVs and Video Sources

11-16-2011, 07:15 PM
Re: Lg 42" plasma model p2pc3d-ud

Doesn't seem to work on my set, it ask's the passwd for both and pushing other menu button just does nothing. only screen view returns to normal. Have to search for the thread.

EDIT: No problems, got the menu open holding both menu buttons on simultaneusly. AC detect..suprise...

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Last edited by slappala; 11-16-2011, 07:26 PM.
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slappala replied to LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

in Troubleshooting TVs and Video Sources

11-16-2011, 07:03 PM
Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

Thanks,

I saw today a 200A clamp for 28$ to use with a multimeter at a local electrics store, will go on and buy it, need it anyways in future.
They even have temperature cameras, but rent is 50e or something for a day..

The VA 60.v line is a good candidate for the root cause..Don't remember if the 15.v for IMP chip is made from this line or the VS line..

luckily I can use the new caps on my tubeamp projects.

EDIT: Got the service menu open by...

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Last edited by slappala; 11-16-2011, 07:54 PM.
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slappala replied to LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

in Troubleshooting TVs and Video Sources

11-16-2011, 09:49 AM
Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

Ok, sadly I was right..no help with the new caps...

the big Caps also were about 80-87% from nominal value when new. ESR was about 85mohm-45mohm depending on the cap. Old caps had about 4-5 times more ESR, but capacitance readings were the same level as the new ones.

Rubycon was little better. Panasonics seem to be on the 80-85% from nominal marking when new..

I guess these high voltage caps are made for less Uf than specced. Also ESR is somewhat high with high voltage caps...

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