LG 1919s no power

[swen_blueneon]

Hi guys..I've just read the article about bad caps in LG L17NT-A..the PSU PCB is little different than in mine, but it's the same thing.

Ok, monitor was working, and then just go black..
When I have opened the case, i saw bad cap 1000uF/16V, ok, and the main fuse 3.15A was dead too.
I've ordered all the caps, the list is the same as fore the above LCD, and changed them...and when I have connected everything, monitor has powerd up, by itself directly after plugging power chord, for about 3-4 seconds, i saw OSD and again dead..LED was green, and when it goes black LED changes to orange an in the end, no light.

But, when monitor is dead, but connected wo my wall socket, i hear some wierd noise from step-up transformer (PT-002134-2)..something like crc...crc...crc...crc, and nothing happens.

The voltage over C101 is around 315V (I'm in Europe - 230V AC)

And all other voltages are ok, but the only thing I'm little suspicious about is 5V rail...i get 2.5-4.8V and it's constantly changing..


Can anyone please help..just to tell me if this step-up trafo is the reason that mon is not powering up or what?!

here are the pics of PSU and controller
http://img507.*************/img507/5699/igp4850.jpg
http://img252.*************/img252/7824/igp4851.jpg
http://img809.*************/img809/1624/igp4852.jpg
http://img441.*************/img441/5548/igp4853.jpg

[alexanna]

Re: LG 1919s no power

^
The 5v jumping is a problem.
Is the inverter section protected by a fuse?
There is a possibility something may be overloaded in the inverter section causing 5v to be unsteady.

[swen_blueneon]

Re: LG 1919s no power

As far as I can see, there is only one fuse, on the mains...I have replaced original with T 2.5A, cause I haven't got T 3.15A, but this can't be a problem.

p.s. I've replaced the X201 14.31818MHZ, but nothing...the step-up is still producing the same wierd sound.

[alexanna]

Re: LG 1919s no power

As far as I can see, there is only one fuse, on the mains...I have replaced original with T 2.5A, cause I haven't got T 3.15A, but this can't be a problem.

p.s. I've replaced the X201 14.31818MHZ, but nothing...the step-up is still producing the same wierd sound.

Long distance feeling as to what's happening. Something is causing the P/S to start and shut down over and over.
One possibility would be a problem with the inverter section, If there was a fuse for the inverter removing it would disable it. And see if the 5volts becomes steady.
There would be no back lights but the power button may start working and we may be able to see an image on the screen with a bright light on it.
It's always best to have a signal going to the monitor for this.

[tom66]

Re: LG 1919s no power

A "cric" sound every few seconds is a classic case of a bad startup cap, bad charging resistor, bad output diode or a bad SMPS controller. The two most common are the startup cap and output diodes.

A 2.5A fuse could cause problems, is this the mains fuse? It will be designed to handle the inrush from the charging capacitor. You monitor may work for a few days or weeks with it, but it would be advisable to change it to the correct 3.15A.

I can't see the pictures. It would be better if you uploaded them using the manage attachments function.

[swen_blueneon]

Re: LG 1919s no power

Images are fixed now..they are just links, because pics are big so you can see details

I'll check the diodes, and caps again, and let you know what happend!!

p.s. it is mains fuse,..i'll go to store for new 3.15A

[tom66]

Re: LG 1919s no power

Replace the capacitor I've highlighted. You can use a general purpose one. If this still doesn't work, then at least we know this wasn't at fault.

Test the diode near the capacitor I've highlighted. Use your multimeter's diode mode. Test it with the positive lead on one end, negative on the other; note the reading down, and then reverse the leads and test again, noting down the reading. One way should give OL or "1 .", the other should give a number from 150..750. [Do this while monitor is OFF and UNPLUGGED!!]

What's the axial lead cap? Did you replace that or is it original?

The devices on the heatsinks I've highlighted - take a closer picture of the underneath of the board where the components are and also a more detailed top down (not side on) picture of this area.

[swen_blueneon]

Re: LG 1919s no power

This one axial cap is replacement, but same as the original 0.47uF 50V
I have mesured D102 you've highlited, RED->BLK=528; BLK->RED=1, so I think it's ok.

Capacitor replaced with new one 33uF 63V, nothing happend, still the same mistery
BTW can you tell me what values are used for this general purpose capacitor?

here's the link for service manual:
http://www.eserviceinfo.com/download...%20L1919S.html

here's the link on YouTube...my 5V output and misterious noise
http://youtu.be/cWftPJ6gX0E

here are pics from selected area with caps
http://img62.*************/img62/4238/igp4858.jpg
http://img252.*************/img252/3375/igp4859.jpg
http://img717.*************/img717/1439/igp4860z.jpg
http://img806.*************/img806/6991/igp4862.jpg
http://img713.*************/img713/321/igp4863.jpg
http://img202.*************/img202/126/igp4864t.jpg

[swen_blueneon]

Re: LG 1919s no power

Long distance feeling as to what’s happening. Something is causing the P/S to start and shut down over and over.
One possibility would be a problem with the inverter section, If there was a fuse for the inverter removing it would disable it. And see if the 5volts becomes steady.
There would be no back lights but the power button may start working and we may be able to see an image on the screen with a bright light on it.
It’s always best to have a signal going to the monitor for this.

Just tried once again putting the power chord in socket and I saw for a little bit orange light on LED, and than goes off.
Can't figure out how to stabilise 5V...maybe new caps again? :$

Tried connecting LCD without backlight, but no picture was displayed...same problems

[selldoor]

Re: LG 1919s no power

Capacitor replaced with new one 33uF 63V, nothing happend, still the same mistery
BTW can you tell me what values are used for this general purpose capacitor?
]

Without a topdown pic we cant see the numbers on the board but you can see what the values should be from the schematic by matching the numbers from the board to the schematic BUT you should replace like with like in case
the board is a newer version than the schematic.
It looks like it begins 10? so is on attached list?

[tom66]

Re: LG 1919s no power

Thanks for those.

Test the circled components. With the monitor unplugged and off, use your meter's diode check to test all combinations of pins, forwards and backwards. 1-2, 2-3, 1-3, 2-1, 3-2, 3-1. For both devices. Then report the results. We are looking for approx. 150 from 1-2 (or 2-1) and 2-3 (or 3-2). A zero result, or a number under about 50, indicates a failed (short circuit) diode.

---

The 5V isn't unstable, it's the power supply that's switching on and off because it's not charging Vcc. This can be caused by a shorted diode, bad startup cap or excessive load on the output, among others. More or different capacitors probably won't fix the problem.

[swen_blueneon]

Re: LG 1919s no power

@selldor - here's the pic from above
http://img823.*************/img823/6336/igp4867.jpg
this schematic is newer I think..
Here caps start with 20, except those two near mains they are 103 & 105
202- 1000uF 25V
203- 680uF 25V
204- 1000uF 25V
205- 1000uF 25V
206- 1000uF 25V
207- 470uF 25V

some of them (1000uF) were 16V, but to be safe I've used 25V


@tom66
I've mesured D201 and D202

D201
RED->BLK
12- rising till 1
23- 0
13- 0
BLK->RED
12- rising till 1
23- rising till 1
13- 0

D202
RED->BLK
12- rising till 1
23- 207
13- 0
BLK->RED
12- 0
23- rising till 1
13- 0


OK...now I get clearer picture what's wrong

But look at this...I've held Power button and pluged in power cable..monitor powers up, i see OSD, saying ''Check Signal Cable'', and LED lights green...but step-up transformer makes irritating sound, HV noise that you can hear in your brain

and i'ts working, but when power button pressed again, monitor turns off, and can't switch it back on for about 15 seconds, and then I've go with the same procedure as I have mentioned above and it turns on again...

[tom66]

Re: LG 1919s no power

OK...now I get clearer picture what's wrong

But look at this...I've held Power button and pluged in power cable..monitor powers up, i see OSD, saying ''Check Signal Cable'', and LED lights green...but step-up transformer makes irritating sound, HV noise that you can hear in your brain

and i'ts working, but when power button pressed again, monitor turns off, and can't switch it back on for about 15 seconds, and then I've go with the same procedure as I have mentioned above and it turns on again...

Diodes are good.

Looks like a strange case of bad capacitors. I would say replace all the secondary capacitors with low-ESR capacitors from good brands like Chemicon, Rubycon, Nichicon and Panasonic. Panasonic FC is popular here, but Rubycon ZL/ZLH/ZLJ, Nichicon PW/HD and Chemicon KY/KZE are all good alternatives, I've used them all.

[swen_blueneon]

Re: LG 1919s no power

Tnx for the help
I have recaped with noname caps, then with Jamicon..

BTW, when I plug VGA cable in and try with push power button and plugin in power cable, again nothing happens...no picture, just this irritating ''crc'' sound..

I really have no ideas what else can it be..
The guy in electronics shop tells me that LG/Philips have trouble with PSU, and the are tricky to fix...he has Philips LCD and he says that he have changed twice all the caps and ICs and God knows why monitor at first wasn't working, and then in one moment it worked and it's now working...I don't get it...

All the errors can be fixed with recaping, but in all cases...ok most cases I don't see that mains fuse is blown...like mine..and I think that here's something bigger than just bad caps?!?!?

[tom66]

Re: LG 1919s no power

Tnx for the help
I have recaped with noname caps, then with Jamicon..

BTW, when I plug VGA cable in and try with push power button and plugin in power cable, again nothing happens...no picture, just this irritating ''crc'' sound..

I really have no ideas what else can it be..
The guy in electronics shop tells me that LG/Philips have trouble with PSU, and the are tricky to fix...he has Philips LCD and he says that he have changed twice all the caps and ICs and God knows why monitor at first wasn't working, and then in one moment it worked and it's now working...I don't get it...

All the errors can be fixed with recaping, but in all cases...ok most cases I don't see that mains fuse is blown...like mine..and I think that here's something bigger than just bad caps?!?!?

Jamicon are not good capacitors.

However I would say you have a problem with the PSU controller or an output problem. How is the +12V output? Could be a shorted inverter.

[swen_blueneon]

Re: LG 1919s no power

I'll try to get caps you have mentioned...maybe tomorrow, or after NY.

Hmm...+12V when LCD is not connected, and not working (no picture) voltage is +17.5V, but when LCD i connected and still not working it +16.3V

[tom66]

Re: LG 1919s no power

I'll try to get caps you have mentioned...maybe tomorrow, or after NY.

Hmm...+12V when LCD is not connected, and not working (no picture) voltage is +17.5V, but when LCD i connected and still not working it +16.3V

That high voltage is characteristic of a bad capacitor (one or more.) The ripple is too high.

Test the voltage at the negative end of that diode near the startup cap, relative to the negative lead of the main capacitor. This is the Vcc voltage.

[swen_blueneon]

Re: LG 1919s no power

Voltage on diode is 9-10V

Also tested FAN7601 Vcc is 9V (pin 7+ and 5-)


Just supid question to ask, but...can U201 cause trouble in 5V line?

[tom66]

Re: LG 1919s no power

Voltage on diode is 9-10V

Also tested FAN7601 Vcc is 9V (pin 7+ and 5-)


Just supid question to ask, but...can U201 cause trouble in 5V line?

What is U201?

Is the crc-crc-crc sound occuring approximately two to five times per second, or is it a continuous tone?

Just checked the FAN7601 datasheet and it specifies a minimum startup threshold of 11-13V and an operating voltage of 7-9V. This would suggest your Vcc is too low, perhaps because of a problem on the secondary side.

[swen_blueneon]

Re: LG 1919s no power

U201 is a three-terminal adjustable shunt regulator, it's near D202 and all 1000uF caps

This sound is occuring 2-3 times in a second, but when I have powered up LCD and saw OSD, it was a continous sound.
p.s. you can hear the ''crc'' sounds in my video just few posts above


I'm just looking at datasheet of FAN7601..but voltage on Vcc pin is 9-9.5V, startup voltage havent mesured right now, but if I remember right, it was 11V.