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

[tom66]

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

Check the AC_DETECT pin before and after the failure. If it drops to zero it's probably your fault.

Not figured out yet what causes the AC detect on these TVs to fail but it seems to be very common.

[slappala]

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

[slappala]

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..

[slappala]

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.

[slappala]

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 on/off...

Less red sparks also.

PS: AC detect/protection was the fault that kept shutting it down.

Have to add fans to the STK chip cooling sinks if it works now to keep it cool in the future. I have not changed the Z-sus STK chip.

Some advice on the STK chip..I found it impossible to use my soldering station(blower and normal) to take the chip out..even if cleaning of all the excess solder from pins some of the holes are so small that the residue will be enought to keep the pins attached.

You should have some special long tips or air ducts for welding station to get it off with welders and be able to heat all same side pins at the same time...

Or do as I did..I desoldered big caps and big coils that were on the way and just used cutter to cut pins from the chip. Then took 1 pin at the time of and cleaned the pads. Worked like a charm.

[tom66]

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

Just for the sake of eliminating the fault, check the AC detect.

You can disable it. The only downside is if the power fails, the speakers make a "pop" sound sometimes. It does not cause EEPROM corruption as far as I can tell.

[slappala]

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

[slappala]

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

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 holding both, remote and tv menu button simultaneusly for 5s. AC detect had 13 hits for shutdown. Don't know if there is a counter that will zero this from fault memory when set is sitting off mains for some period of time and then it will let you start the TVt until gets a new ac detect error.. BUT When I can get it going I can watch the tv 8h or more easily..it just does not make sense to me why the problems comes only at start up phase.. since all the components are quite hot during running.

It just makes it really difficult to find the primary cause of the starting problem , I don#t want to toss in too much money for this old tv..can get new ones for 600$ here..alltought they last the same 4.y max porobably ..

[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

[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? :/

[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

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

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

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

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

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

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.

[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

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

[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!!