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

[slappala]

Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

Same here. No idea how it fixes it but it does. Seems very common with LG plasmas.

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 fail completely I will just use it like it is

[tom66]

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 fail completely I will just use it like it is

I figure the same. Pins 3 and 4 make the optocoupler seem always on. It might be the PFC bus caps aging or the TL431s being damaged. (These sensed the voltage on the primary on my model.)

[MoDu]

Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

How long have you had this "hack" force tv to not auto-shutdown?

I've had all the problems described here, even went as far as replacing all big caps and even a whole YSUS board, but alas, it remained the same.

I shorted out the suggested pins on the opto-couplers and so far so good.

Will this kill my tv in a few months? Or will it just keep going until a fuse or a IC burns?

[tom66]

Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

I had it running for a month, but sold the TV on after that due to the LG "sparklies" issue.

The only disadvantage that I can see is the audio doesn't mute on power off, so you'll get a loud crackling sound. This is a common phenomenon with audio amplifiers. Some can detect the failure of their supply voltage and mute immediately, whereas others require an external signal. AC detect provides this signal, along with the signal to the processor to tell it to keep running.

[MoDu]

Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

Audio is a non issue for me, I don't use the TV's audio at all.

I was able to easily fix the sparklies with some tinkering on the Var resistors, they're now invisible at a regular viewing distance.

So my only concern right now is whether this will destroy what's left of the Z board.

[tom66]

Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

I doubt it will do any damage to the sustain boards. My 42" actually ran for half a second with this bridge made, you could see picture slowly fade out before it cut out completely, so it does shut down reasonably cleanly.

The speakers will make click noise even if nothing normally comes out of them, so to avoid this simply unplug the speaker connector on the AV board (board with SCART etc on it.)

[MoDu]

Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

Thanks for the tips.

[MoDu]

Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

I tried turning on the sound, to see if I could hear the speaker thump you mentioned, but it was barely noticeable. It only happens when I unplug the cord, simulating a power outage.

BTW, disabling the speakers in the menu is enough to NOT have this side-effect.

[tom66]

Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

Great, so there is no issue. Yes, it only happened on mine when power is unplugged, and only then on bright scenes. Dark scenes caused no click. I figured this was due to the standby supply lasting longer than the main supply so the TV could recognise a power failure and cut off the speakers.

[er_rusty]

Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

Okay, pin 4 on the optocouplers is on the phototransistor side.

They're the only signals coming FROM the primary to the secondary, normally the signals go to the primary side from the secondary.

Need a closer pic of under these devices.

You will probably need to place a solder bridge between pins 4-3 on both optocouplers. That's how I fixed mine.

Hi to all!! I'm new, I have a LG 42PC1RV-ZJ plasma TV that had the same symptoms slappala TV. I think that the solution can be the same.

Please, i don't understand very well what i have to do:
Maybe I have to place a solder bridge between pins 4 of one optocoupler to pin3 on the other???
Or I have to put a solder bridge between pin 4 of a optocoupler to pin 3 on the same in booth optocoupler?

TOM66 help me please!

Thanks a lot!!

[tom66]

Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

Pin 4-3 on BOTH optocouplers. i.e. 2nd choice.

Only bridge the devices which have 4-3 on the SECONDARY (isolated side.) Do NOT bridge them on the primary.

[er_rusty]

Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

Pin 4-3 on BOTH optocouplers. i.e. 2nd choice.

Only bridge the devices which have 4-3 on the SECONDARY (isolated side.) Do NOT bridge them on the primary.

Thank you!

[benfinland]

Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

What are these optocouplers? And where? I was wondering about bridging them to see if the tv will fire up

[tom66]

Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

Not relevant to your model unfortunately.

[er_rusty]

Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

Pin 4-3 on BOTH optocouplers. i.e. 2nd choice.

Only bridge the devices which have 4-3 on the SECONDARY (isolated side.) Do NOT bridge them on the primary.

It works!!
Thank you again!!

[tom66]

Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

This has to be the tenth TV with this issue so far fixed. Glad to hear, enjoy your TV!

[Shipmaker]

Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

Hallo everybody I m new on this board!

Thank you for your solution, because i v got the exactly same powersupply in
my LG42PC1RV and in nobody could help me, but now!
I also recogniced while I looking tv that a little green snow apperes, to see
in black parts of tv picture and while changing programm.

But my Question is : How do you bridge with solder or with a wire?

(Please, forgive me my bad english, i am german)
Thanks!

[Alastair E]

Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

You can bridge the opto with blobs of solder done carefully this is fine.
--But,--As Tom says--Only bridge the one side of the optos.

The green spots can be adjusted out sometimes but the official cure is a Software Update to the Contol-Board.
--Let me know if you want control-board update, I have the complete kit to update lots of LG sets--including the PC1 series....

[Shipmaker]

Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

Thank you for the fast reply,

now i try out to fix my tv with an solder bridge!

I dont now if this kind of Modell LG 42 PC 1 RV is able to update on software side
but i will take a look on my service manuall and tell you if it s possible.

But again Thanks a lot!

[Alastair E]

Re: LG 42PC3RA SMPS power_ysus problems on/off/on click and fixes

According to my data--its updateable, Its the Control-Board firmware that needs doing, not the mainboard or the set itself.

Tell me the numbers written on the back of the banel metal-work, be something like 42X3####