LG L1953S doesn't power on

[budm]

Re: LG L1953S doesn't power on

LED will do, another place to monitor to see if the running power supply section that keeps the SMPS IC running by supplying the voltage to VCC pin 7 of the IC, I want you to put LED with 1k resistor in series and attach this to pin 7 of the SMPS IC or across C103, This LED should blink on also, if it does not, then that may explain why the SMPS does not stay running.

[Joun]

Re: LG L1953S doesn't power on

Since I don't have incandescent lamps I will connect leds with suitable resistors and right polarity..

[selldoor]

Re: LG L1953S doesn't power on

How about checking near the transformer - should voltage at D203 be 5v?

[budm]

Re: LG L1953S doesn't power on

We are trying to find out why you do not have the 5v output as you have indicated, but you do have 12v, but since the5 and 12 are generated from the same transformer tehn the only thing that can be due to fault circuits in the 5v rectifier/filter section, open winding for the 5v, etc, so with the lamp, you should be able to see if the 6v lamp will light up for seconds also.

[Joun]

Re: LG L1953S doesn't power on

You want to me use something like that to watch the voltage on outputs without a multimeter or for adding a load and see if it has the same behavior?
I have just notice that the +12V output drops at the same rate regardless I keep it plug or not..I mean if I keep it pluged or I plug it for half a second and unpluged it then it makes no difference.

P.S It takes about 6 minutes to drop from 14V to 1.5. It seems to me like a capacitor discharging without any load at all..

[budm]

Re: LG L1953S doesn't power on

The easiest will be using small grain of wheat 6v, and 12v lamps connected to the outputs.
http://www.radioshack.com/product/in...ductId=2102814

http://www.radioshack.com/product/in...ductId=2102815

These are good when work on LCD monitor power supply.

[retiredcaps]

Re: LG L1953S doesn't power on

You should initially see something at the 5V output during power on.

Min/max on a multimeter would find that really easy upon power up.

[jetadm123]

Re: LG L1953S doesn't power on

I'm still on the fence as to whether the SMPS chip (U101) is bad or not. Your measurement of 9.9V on pin 7 meets the 9-10V requirement in the service manual. Unfortunately, no scope to measure the output of pin 6. If it wasn't working, then you wouldn't get the initial 12V output when you first turn on the monitor. What really confuses me is that the 12V and 5V outputs are driven by the same transformer, but you get an initial 12V and no 5V output. You should initially see something at the 5V output during power on. Still sounds like a short somewhere. You say that the 12V output drops over time. Does it go down to 0V or stop at some voltage? Does pin 7 of U101 also drop?

[Joun]

Re: LG L1953S doesn't power on

Well all caps were and have normal ESR.Soldering is OK,PCB doesn't have any shorts of any kind.My Atlas component tester can't check optocoupler so I replace it with a new one.
Voltages on SMPS IC:
pin1 276V
Pin2 270mV or something.
pin3 has pulses that the analogue bar of my multimeter measures about 5V
pin4 has pulses about 18V
pin5 GND
pin6 0V
pin7 9.9V
pin8 pulses about 5V

I understand that the pulses I see are some kind of a waveform but I don't have a scope to check what they look like..

And you said in post 4 that voltages were without other boards attached?
You should be connecting it all up to check output voltages.

Not really..I can check for +12Volts.If there aren't any I don't think it will ever come alive..
Thank you for your time.

[selldoor]

Re: LG L1953S doesn't power on

How about answers to thes qs
Did you replace the caps- what make/series are they - have any not been replaced,what make series are they?
Can you check on the bottom of the board the bottom pin on d201 looks cold? (gap in solder)
Near what looks like C02 there is a solder splash can you check it hasnt burnt through to the trace - clean it off.
C203 the leg looks like it is just sticking through the solder (cold?)
What is the triangular bit of soldering near D105?
I am only asking as I cant see enough in the pics

Can you test the optocoupler http://www.datasheetarchive.com/PC82...tml#datasheets

And you said in post 4 that voltages were without other boards attached?
You should be connecting it all up to check output voltages.

[Joun]

Re: LG L1953S doesn't power on

I will check it again if you want ,but can you tell me what are you searching for?A short on pcb or at the ic itself? I'm just trying to understand the way you're thinking..

P.S I'm checking voltages now..

[Jasgriff]

Re: LG L1953S doesn't power on

Can you give us the readings.

What voltages are you getting off each pin?

[Joun]

Re: LG L1953S doesn't power on

Yes,didn't find any..

[Jasgriff]

Re: LG L1953S doesn't power on

Have you checked the smps controller for shorts?

[Joun]

Re: LG L1953S doesn't power on

Anyone?

[Joun]

Re: LG L1953S doesn't power on

I replaced 0.47uf capacitor with a 1uf but nothing changed..It had exactly the same behavior.
So am I looking for an SMPS controller ic or do I have to check anything else?

[budm]

Re: LG L1953S doesn't power on

I think the LF001 is the LG in-house P/N.

[Joun]

Re: LG L1953S doesn't power on

Yes it does ,nobody knows LAF0001 on the net..

[budm]

Re: LG L1953S doesn't power on

SPec for FAN7601 SMPS IC, it looks like it has the same pin out as LAF0001.

[Joun]

Re: LG L1953S doesn't power on

OK, so I'll look for a new SMPS IC and if that fails also I'll buy a new board(and fix this one too)
Thank you for your time.