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

Could this be an surge/ over /start current protection issue?
Higly unlikely that the coils/coil would be bad?

darned I don't have a nice way to measure where the current is sucked at the start..

[slappala]

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

Voltages are allright.

Only thing that the 3.3v detection line is 5.v, but probably ok and as should.

I got the tv set on again no problem for around 10 times before it wen't back to failure mode.

We'll when doing measurements I also lost the thermal fuse again since it gets so hot during the on/off/on syndrom. I can do the fault finding without it I guess and since I would otherwise have to wait for it to cool down before starting it up again and that would take too long time for me..

I hope the component would just give up ..

Strange thing is that when ever the set is sitting without power cord for a while I can start it no problem.. the longer I use it, the longer it must stay off power line untill I can start it again. Then no problem again..

It also does not shut down when I can get it going..

I guess that would mean there is eather CAP problem on Ysus or something else related to electrical storage/temperature.

If I disconnect the ysus I can start it everytime and vs and VA jump right up as should..

Also the vs on 5.v detection line is not going up fast enough and has fast peak value of around 2.3v when the set is in failure mode, right at the end before the mainboard cuts the power again and starts trying again...

So just TV can't get the Vs line up with Ysus connected enough fast and TV control board resets the starting sequence..Or the vs on 5.v detection line has more delay than the Actual VS line..

These are the only problems I have found..

I just can't imagine that the Ysus boards IC or the buffers could function like this, drawing current on start when Caps full/warm and then functioning normally as I get the TV set up..

I'm dismantling the set and doing some ysus board cap measurements
again with the new esr meter..

I also found funny behaviour in some of the lower ysus small attachment board capacitors after power down and failure mod (-176v line caps). There was a funny dip on the oscilloscope reading..

frustrating when this fault is not on all the time..



EDIT: Main caps on ysus board fine

[muskin]

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

slappala did you check the output on the power supply board where the cable goes to the Y-sustain and the Z-sustain board? I think it should be 5v. Also did you check the plugs down on the bottom of the power supply board. 3 plugs, I disconnected these and found that I was losing the 3.3 volts on the middle and the one on the right. I haven't had time to trace them back to where the lose is yet.

[slappala]

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

Does anyone know the extra service menu code and does it contain the shut off record? Or do I need service remote control for seing the fault codes?

[slappala]

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

Managed to measure the big CAPS today with the new ESR meter and big capacitance meter.. I think the caps are allright even if somewhat bulged.
ESR was low and capacitance in specs(I guess the capacitance is not dead accurate with this meter. Showed about 80% for even new CAPS that I had lying around. Rifa caps measured A OK and spot on). Also they are not shorted..

We'll It's back to the drawing board...Again must put the set back together and do some measurements without the ysus..

Last time I test used the set I could not get it on again after taking the cord off so what ever it is it must be getting worse. TV worked great for many hours, but then won't start..Hope I have some time to play around with it.

Now I'm happy I did not rush into bying the Big caps before the new meter arrived.

darned..I thought I found the issue from the powerboard, but not..have to reconnect the new resistor/thermal fuse and start fiddling with it..(Just has to pull the cord after few starts so I don't burn it) For sure this is the last Plasma I ever fix(If I get it fixed) cause there just isn't enought reasoning to use all this time for fault finding..

Now why would the Ysus board not show any shorts and the tv worked after got it going if the Ysus board would have some trouble..also the voltages on SMPS were somewhat ok ones started and before start. this thing is driving me grazy..

No I'm thinking it must be protection circuit that is giving me the hard time..has to go thru the start sequence also again.. :/

So nobody has the schematics for the SMPS? Nor good schematics for the Ysus board?

[slappala]

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

some clarification, I still don't have the powerboard schematics, the service manual for the 42PC3RA don't have them, only circuit board diagram that is version 1 from this power board and not up to date with my board anyway .. so not much help in deeper re-engineering work since I found also some wrong component values. This is by the way Euro version, but says US at the back panel..maybe allready fixed frankestein..never know.


Hmm..while watching a test movie(+couple halloween refresments) I think I should go thru my old stuff and find a fan for the Zsus board also.. I wonder how long these Plasmas would have lasted If LG had made some minor improvements..

I hate modern engineering..

Remember one time when I was a mechanical engineer when my boss asked what the fuck is this 10cent washer here..I told it works better..He asked is it mandatory..I said we'll..but it will last longer. He said Yep. Toss it..
Products sale price was 750$ and profit 73%..yearly sales about 1500pcs

Ok, thats all for off topic..going to find me a Fan from surplys boxes (Installation tomorrow, no more plasma fixing today )-->

[slappala]

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

Component hints to check would be more than welcome. Service manual I allready found from Google..

[slappala]

Hi,
New to the forum, but here it goes..

I got this tv unit used that the previous owner said go off sometimes and would be hard to start, but TV sometimes still started. Problem was this.

First night I used the unit 8 hours and saw nothing wrong, next day..on/off/on/off syndrom..

After a while without mains power it started again.
Usually after this starts the on, click, off, on, click etc. endless cycle..after a long while it would maybe start, but taking it of the mains usually helped.

I unplugged the ysus and zsus boards and ysus board seemed to make a difference..Vs and Va showed ok at start in my scope when only zsus and xsus boards were connected.

off course thought first there is some trouble at the ysus board. so took it off. desoldered some suspicious Caps and they tested all OK (Still waiting my ESR meter tho). All IMP board connections etc were fine and not shorted, vs,Va etc. ok and not shorted..

But it back together to get TV going on again and doing more measurements.
Scope showed that the Vs power goes down slowly on the start all the way to 0.v. I knowed this allready, but without AMp clamp did not know if it was the Ysus board that took it down..or was too lazy to measure the whole start cycle since saw that error situation shutted teh set down..

If I play with the mains cord I can usually get it started when I reconnect the cord when Voltage hits about 80-90V..Voltage also goes down really slowly.

Well..this let me think the problem IS on the power board..So I started going thru it. I also saw the 270uf 450v main Caps on primary E247691 powerboard were bulged a little.

Scoped the voltages, but saw nothing really special when the set is on. Some 1-2.v interference on Va 60.v line (I have since detuned the Va to 45.v..Later more on that)

I also found that the combined 10 ohm thermal/resistor was shot. This sits near by the Zsus connector. Went thru the circuit and I think diodes and all were fine...So. Wen't to a local electronics store today to get some spares.

I measured some inteference from the main 820uf 250v capacitor can top plate (Cathode?) with the scope so thought would change that too if it helps for the Va line interference problems.

Off course no spares on house so the 3 Big Caps are on back order, I replaced the thermal fuse/resistor with 10ohm resistor tied to a thermal fuse that shots at 100'c original would shoot at 142'c so though it would be okay to try it.

Old Caps in place I started the TV carefully and measured the Vs line with the scope. Bingo! Everything went like in the movies. Voltages straight up and when shut down the voltage dropped like normally would really fast to 0.

But it won't function anymore after a while and the resistor pack got really hot after set started again the repeated on/off/on situation and I cut it off.. So I have to change the caps before I can reconnect the 10ohm resistor/fuse. It started ones or twice really nicely with clean Vs signal.

This is the situation today..Waiting for the CAps and new ESR/big capacitance meter then doing some more measurements.

Hope the Caps. are everything I need and I don#t have to dick too deep to the SMPS..I did not find after 2 hours search any schematics from the net..


Any hints for the power board and schematics would be really welcomed..problem is that it for example uses rare n-mosfet on this resistor circuit, Sankens own 2505..So if that is tost I would have to find a replacement for it, but since I don't have the specsheet for it I don't know for example the threshold levels etc. to match it up really nicely and not screw up the rest of the control circuit..


I decided to test the tv some more tonight and lowered the Va and Vs to a 46.V and 174.V. This was lowest that I could with turning the adjusters...Tv picture looks okay for me and since it's dark season here in Finland I think I will leave the voltages down and try to give the Ysus and Zsus boards some more lifetime...Only the white level is grayish, but if this buys the set some 5.years I can live with it.

Also this took care off all the red dots etc. funny shit from the screen. So if nobody says it's not okay to drive the plasma screen with this low voltages I will leave them to that value. original spec on the top corner says 60.v and 186.v +-0.5, but I know LG cranked this baby way too hot for sales purposes...

I also added an old 12.V CPU fan from empty 5.v line to Ysus Sink since it showed some more leak current than the Zsus to the heatsink and commonly fails first.


Any help and hints are welcomed!!!

Power board is E247691 or Sanken 1H328W

Ysus is 6871QYH953A
Zsus is 6871Q2H956A

TV is LG 42PC3RA year 2006..(I guess it#s always freaking cold here since it is still alive ...)

So HELP HELP HELP if anyone has some ideas more than the CAPs..

By the way..when the resistor was back on the flyback/control circuit for start surge I got only very fast one spike from Vs line..it just did not stay on long enough/have crunt to start the screen..


PS: It's my first TV repair, so please bare with me , also too long post to correct all writing mistakes..sorry for those.