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

[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.

[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]

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

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

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?

[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

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

[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

Now the last wakeup line vsON stays on 400ms and led goes off almost simultaneusly.
power comes on for about 300ms and not straight up.

Won't start up the set even with only zsus board connected..both off everything fine.

I noticed that the Vs start edge will take about 200ms with both boards connected and about 100ms with one board.

Hmm..this is weird. I'll bet it will start ok tomorrow morning..

Vs ON control line 5.v signal is razor sharp. I was going to try overrading it, but it has pullup resistor so not so easy.

what causes this error that shuts down the SMPS unit..???

I'm going on in circles so help would be appreciated..

could the main SMPS caps still be bad(when high voltage is applied) even if they checked OK With ESR, Capacitance meter + multimeter..

I'm lost..don't even know now what boards I would try to replace since Can't verify the responsible board anymore. I just wish I would have some more broken components..by the way I found one blackened smd cap on SMPS board by the vs ON line input, but the 5.v signal seems to be ok still..

HELP HELP HELP!!

[slappala]

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

Started ok this morning..ones.

By the way, the main caps measurement values are
820uf ---> 665uf and ESR 0.56ohm

270uf--> 220-230uf ESR 0.36ohm

should be ok? The caps specs for replacement SMPS caps said ESR would be around 0.5ohm range on multible SMPS low ESR alternatives..+-
And tolerance +-20%

PS: How come they are not +20% even new

[PlainBill]

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

Started ok this morning..ones.

By the way, the main caps measurement values are
820uf ---> 665uf and ESR 0.56ohm

270uf--> 220-230uf ESR 0.36ohm

should be ok? The caps specs for replacement SMPS caps said ESR would be around 0.5ohm range on multible SMPS low ESR alternatives..+-
And tolerance +-20%

PS: How come they are not +20% even new

Those numbers indicate the caps are bad. The specs are +-20% of nominal - for the 820 the lower threshold would be 660uF, for the 270, 216uF. The ESR for a low ESR 820µf cap should be below .05 ohms; .07 for the 270uF.

PlainBill

[slappala]

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

Here are some scope snapshots when ysus/zsus are not connected and when they are. boards connected it will not start if has been started recently. Can this 150-200ms difference in VS line risetime cause the shutdown or is the reason somewhere else than SMPS diagnostics..??

I guess I have to scope this tomorrow or late this evening with the boards on and when it starts to make a comparison for starting with out boards scope readings.

If it ain't the SMPS diagnostics that shut down the VS/Va lines what diagnostics there are coming from teh y-zsus boards to the main board??

The voltage drop is almost the same when switched off from the TV on/off switch when the set is on. It's quite fast now with the resistor connected.
Also the blackened component near VS-ON input to mainboard was a resistor and checked ok value. It was included in Clock circuit of the U702. It has ceramic oscillator and it showed to be oscillating to U702 ok..well the U702 control IC would not work if the oscillator would be dead..

Oscillator is saw wave formed so the voltage level is quite low and the signal level dies quickly if measured with scope etc. and causes the micro to reset


I only have 1-channel scope so can't do any timed checks for 2-channels...maybe I have to start looking for one. I would need 2-channels farely often on other projects also.


PS: I don't know exactly the grid readings here..first time I used the USB downloading feature on my scope and it does not allow me to change the grid. measuring range was 50v 200ms. 10 units on horizontal is 200ms.

[slappala]

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

Those numbers indicate the caps are bad. The specs are +-20% of nominal - for the 820 the lower threshold would be 660uF, for the 270, 216uF. The ESR for a low ESR 820µf cap should be below .05 ohms; .07 for the 270uF.

PlainBill

Thanks Plainbill, I will order the new main caps and try them. I was looking at some caps that I was going to order and they had quite high ESR on datasheets even when supposed to be Low ESR and SMPS compatible. Since I just had my first ESR meter I'm still learning and compared the values for the datasheets+some random new caps.

It's quite funny that I have been going circles around this SMPS unit, but live and learn . Hope the caps help. Can you recommend some caps?

I have been looking Panasonics from Farnell..

[slappala]

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

Can't seem to find any really low ESR caps from panasonic for 250v+ volts..hmm.

here is a recent pic (2min ago) from Vs line voltage rise. Now both boards were connected and the set powered up OK. Maybe I have to scope the 60.v line also.

Maybe the caps don't affect this output voltage line? I might as well try to find the feedback line circuit from SMPS voltage line(Vs Va??)to U702 pin and see if that has some explanation to this syndrome..

Can't see any real difference on voltage level or rise time between boards connected - not powering up and -powering up other than a really small dip on the corner there..probably just pure luck it looked like that.

[slappala]

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

Might have to eat my words...this is the next measurement when the set is not powering up..dip is there again. Have to believe it now and buy those caps. Small difference if this makes it tick or not.

EDIT: Added not powering signal from 60v VA line and other when y+zboards are disconnected+powering up..that might explain it more if the U702 snifs this line..looks pretty ugly axels were 20v_200ms

[slappala]

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

OK, here are voltage readings from SMPS U702 control IC feedback pins that I found.

power up succesfull =ON pics without y-z,board connected
not successfull starts with boards on = OFF pics.

Pin27 on U702 comes from 60.v VA line thru 3 resistors, PIN28 has extra resistor/capacitor pack(filter?) but same route to IC otherwise.

PIN21 comes from 186V VS line thru the mysterious N-mosfet..I guess the mosfet is ok . This is the line that comes thru the ones burned 10ohm thermall fuse/resistor+2x10ohm extra ceramic resistors and 2 diodes.(one from each line VS and VA).

When this PIN 21 signal was missing the tv started sometimes also, but signal behaviour was pretty nasty. ones started VS/VA was ok.

I guess this explains a bit of the emergency/fault shut down?

I also firgured out the scope screen grids and the .jpg picture grids..screen has 8x8 grid that corresponds the 60- -60 and 0-160 picture readings.

all pics are 200ms time interval (divide 160pic/8screen=20units = 200ms)

these U702 pics are 2v grid so 60/4 => 15units is 2.v

other pics 50v/scope grid unit---> 15units is 50.v

any toughts about oscillation?
I might as well replace the 60.v VA line cap since that has the most problems..

Also measured VA line with only the zsus board attached, cleaner, but no start. Has to see if I will check the ysus board 60.v line for problems if the new psu caps won't help.

PS: now I will let it sit for a while and wait for the new caps..

[slappala]

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

http://industrial.panasonic.com/www-...A0000PE285.pdf

the ones I can find from farnell are eeted, eetee and eethc..are these ok?
They are rated ESR 0.4-0.6ohms at 120hz..snap ons don't rate ESR. Only ripple.

now I just wonder how much the ESR meters 320khz measuring affects this..so I guess the ESR is off a lot.

and would it be helpfull to add a second capacitor(make double stacks, lowering ESR) or a bigger one. I guess I could go 10-20% higher uf rating or will this screw up the smps control? Would also give some room for choices..

[slappala]

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

ordered panasonic eeted:s 330uf_450v, 820uf_250v and one rubycon zl_mefc 680uf_100v...

There is no list here on Badcaps of these higher capacity/voltage caps..Should be ok.

Were the best specced big ones I could source for a decent price.

I'm still not 100% sure if these fix the supply, but let's see.

[slappala]

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 compared to say 63.v, but new ones were well on the specs.

I have not compared the capacitance meter to others, but it seems consistent with new caps and like I said, only really spot on uf value and ESR I have found from new caps has been with RIFA audio caps 1000uf/63v.

TV worked couple starts again fine and then same problems. Again because off the long downtime I could even hook up ysus and zsus individually and it would start with eather connected..so..

what to do now? :/

[ben7]

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

You say that the TV has to be off longer if it was running longer. That makes me think something else is getting hot, and needs to cool down; so when hot it is somehow shorted, making the power supply click on and off when trying to start up the TV(lots of times there is a startup surge current that gets drawn from the PSU). The values of components do go up and down with varying temperature.

You need to find out why there is a large current going through the fusible resistors when the TV does its on-off thing. The going on and off is from the power supply detecting an overload on one of its outputs. That is a safety feature.

-Ben