LG L1953S doesn't power on

[Joun]

Re: LG L1953S doesn't power on

Last time round you got voltages when you lifted R111 did you ever check D102 to see if it was functioning correctly.

I have check it many times,it is working just fine..

[Joun]

Re: LG L1953S doesn't power on

While the 13V is dropping, what's happening with the 5V? Is it stable, dropping or at 0V?

The 5volts output has 0V.But now after I replace the controller ic I have more or less normal output (12.3 at 12v and 5.4 at 5v) but as soon I connect Vga board, 12Volts starts to drop and 5Volts goes to 0. I have check Vga board with my magnifing lamp,everything looks fine.I have also measure for low resistance paths at 12V and 5V,didn't find any..

[selldoor]

Re: LG L1953S doesn't power on

Last time round you got voltages when you lifted R111 did you ever check D102 to see if it was functioning correctly.

http://www.ehow.com/how_7556262_test-1n4007-diode.html

[jetadm123]

Re: LG L1953S doesn't power on

Well I've got a new controller ic and replace the old one..I now have steady 12.3V and 5.4V.
The thing is the moment I plug VGA board it acts exactly as before: I have about 13V that are slowly dropping 'till it reaches zero.
I must add to that I have the 12.3 and 5.4 voltages only if I add load on 12V output by soldering a led string I have about half a meter long..If output is left without any load at all I have about 17volts which points out there is something very wrong with the power supply board, right?
The most strange of all is that just out of curiosity a have put the old ic back and it acts exactly the same with the new one..

While the 13V is dropping, what's happening with the 5V? Is it stable, dropping or at 0V?

The 17V under no load conditions is probably ok, since the 13V output is unregulated and will increase under no load conditions.

A good focused photo of your logic board would also be helpful.

[Joun]

Re: LG L1953S doesn't power on

Well I've got a new controller ic and replace the old one..I now have steady 12.3V and 5.4V.
The thing is the moment I plug VGA board it acts exactly as before: I have about 13V that are slowly dropping 'till it reaches zero.
I must add to that I have the 12.3 and 5.4 voltages only if I add load on 12V output by soldering a led string I have about half a meter long..If output is left without any load at all I have about 17volts which points out there is something very wrong with the power supply board, right?
The most strange of all is that just out of curiosity a have put the old ic back and it acts exactly the same with the new one..

[selldoor]

Re: LG L1953S doesn't power on

@ Tufi 979
Welcome to the forum-
We can help a lot more if you please post good clear pictures of each board, front and back and close up of connectors, (max resolution 2000x2000 and 2MB) using the manage attachments button, which is found by clicking "go advanced" under quick reply.

Please do not post inline and offsite as they slow down the loading of pages.

Examples of what is needed
https://www.badcaps.net/forum/attach...1&d=1290283049

https://www.badcaps.net/forum/attach...7&d=1280167246

It will be useful if you can say a bit about yourself - skills tools etc.

[tufi979]

Re: LG L1953S doesn't power on

Hi i have problem with exactly the same Power board , only i don't have any output voltage nether 5 nor 12v. But R108 after plugging in keeps burning out slowly. I'm running out of 47k om resistors. What could be the problem , im guessing some short circuit but i cant find it. Supply voltage correct 240v. big cap ok. No power on secondary circuit.

[Joun]

Re: LG L1953S doesn't power on

OK, I will order one and post results..
Thank you all for your time and patience.

[budm]

Re: LG L1953S doesn't power on

Yes.

[Joun]

Re: LG L1953S doesn't power on

Yes the voltage on Vcc is still 9.8 volts..
So? Is it a faulty ic after all?

[Joun]

Re: LG L1953S doesn't power on

I have edit my post..

[budm]

Re: LG L1953S doesn't power on

I edit my post as well after reading your edited post, now time for me to think what is happening, so do you have voltage at the VCC pin of the IC, if you do, then there is internal leakage inside the IC (failed electronic MOSFET switch between pin 1 and pin 7) and now it is trying to run off pin 1 supply by R108 (47K) but not enough current to run it properly.

[Joun]

Re: LG L1953S doesn't power on

No, I don't have a scope,maybe it is time to get one..I have some other instrument a have to buy before that(electrical installation tester ) for my "day job"..
Because everything else seem to be OK,is a faulty ic the last alternative?

Well I understand nothing..I have just did what you suggested and remove one leg of r111..
To my BIG surprise, I have constant 12.8Volts output and at 5 volts I measure 4.5 volts with multimeter but I see the leds pulsing with 3-4Hz..
Well I'm waiting for suggestions..I can't work on that now ( I have to go to sleep ) but for the first time I'm getting some positive resuls.Thank you very much..

[budm]

Re: LG L1953S doesn't power on

Do you have Oscilloscope? The whole thing still does not make sense to me yet since the VCC power supply is working unless there is internal leakage between pin 1 and pin 7 inside the IC so the current is flowing through R108 and comes out on pin7. You can try lifiting one leg of R111 and see if the LED will still stay lit.

[Joun]

Re: LG L1953S doesn't power on

Of course you are right..It was a very small dot and didn't see it.

It is very common practice to do one winding and tap off the section for the voltages you need.

I know that well I am an electrical engineer.. Well all windings aren't open so can I check anything else?

[budm]

Re: LG L1953S doesn't power on

Pin 7 and 8 are connected together a the junction of R201 (left leg on the SCH), Anode of D202, D203. You have to magnify the the drwaing to see the connecting dot of the junction. It is very common practice to do one winding and tap off the section for the voltages you need.

[selldoor]

Re: LG L1953S doesn't power on

Well what voltages do you get on the transformer 6-8 and 7-10 ?

[Joun]

Re: LG L1953S doesn't power on

I think you didn't observe how the windings on secondary go..There is one winding on 6-8 and another on 7-10. The 6-8 winding is for 12Volts output and the 7-10 is for 5volts.I don't see them in series..(am I missing something? ) I can't see how is possible to have a reading on 6-9 and 6-10 since they are on different windings..
The windings are measuring OK, nothing is open. I have check multiple times D202/D203 and every other semiconductor on PCB,they are fine..Fusible resistor R111 is OK..

[budm]

Re: LG L1953S doesn't power on

"On the Vcc pin of controller I have constant voltage, no pulses or anything, led lit steady.." So it stays lit and never goes away, but the 12v and 5v are not working, correct?

Now that does not any sense at all. There are 4 windings on that transformer:
Pin 5&3, the primary drive winding.
Pin 1&2, the SMPS running supply for the VCC once the SMPS IC kick started on pin1.
Pin 6 &8 is for 12v, the winding is in series with the winding 7&10 which is for the 5v power supply.
Take the continuity reading of 6-8, 6-7, 6-9, 6-10.
Since you do have VCC that means the primary drive circuits are working to ptoduce AC voltage on pin 1&2 which feeds R111 FUSIBLE RESISTOR, and then the Rectifier Didoe D102, the output on the Cathode side is then filtered by C103 (33UF/50V).
Just think of it this way Pin 1 of the IC is like a batteries in your car, you need it to start the car, once the car is running, the Alternator (WINDING 1&2 is like the alternator) will take over and run the car (on pin 8), the batteries then can be diconnected (whick it does automatically inside the IC).
Check D202/D203 to see if it is OK.

[Joun]

Re: LG L1953S doesn't power on

Well, LED trick is really neat..
On the Vcc pin of controller I have constant voltage, no pulses or anything, led lit steadily..
On +12V I have voltage that slowly drops as measured with multimeter but:
On 5V I have I pulse for half a second or less and then nothing.What is more strange is that if voltage on 12V output doesn't drop to 0 it is exactly the same if I have pluged it or not.I mean the only way to get the 12V output again is to wait for it to drop to 0 and then plug it again or to short circuit output( I quess that discharges capacitors) and plug it again..