LG L1953S doesn't power on

[budm]

Re: LG L1953S doesn't power on

It depends on the spec of the IC for the VCC operating range, the spec will tell you the OV/UV (Over/under Voltage points). Your power supply is pretty basic designed.
Check the fusible resistor R111 (4.7Ohms), and C103 (33uf/50v), and the 0.4uf taht you had already checked. By the way service manual has real great explanation how it works.

[Joun]

Re: LG L1953S doesn't power on

Your service manual is exactly for my power board.Service manual I have posted before was more or less inaccurate.
with its help I see that the voltages on controller are OK but I don't have a scope to check waveforms.I have an Atlas component tester and power mosfet seems to be fine..

[budm]

Re: LG L1953S doesn't power on

I extracted the pages form your post #1 service manual PDF.
Ritght now it sounds like the circuits started up (pin1 is the kick start input pin which gets the initial DC from the main DC filter cap) and then shutdown, which can be due to bad running power supply which is generated from the winding of the transformer which feeds R111, D102, filrter cap C103 then feed VCC pin7. You need to check those componenents.
By the way, measure the resistance between pin 7 and pin 5 of the IC also to make sure it is not shorted out.

[Joun]

Re: LG L1953S doesn't power on

All of the components you mentioned are checked allready.(many times) I will replace C105 tomorrow (hopefully) and see how it goes.
Is it possible for SMPS to go bad?

[Joun]

Re: LG L1953S doesn't power on

I extracted the pages form your post #1 service manual PDF.

Are you sure?Mine is different(look at U101, yours is the right one for my board)
Resistance between 5 and 7 is 500+ KOhm so no short..

[budm]

Re: LG L1953S doesn't power on

I down load that from your post #1. Yes, the SMPS IC can be bad.
Correction!: you may be right, the manual I down load from elektrotanya.
I just do not remember how I match it to your 1953
The FAN7601 in you manual seems to have the same pin out as LAF0001 as shown in my extracted page.

[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.

[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

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

[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

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?

[Joun]

Re: LG L1953S doesn't power on

Anyone?

[Jasgriff]

Re: LG L1953S doesn't power on

Have you checked the smps controller for shorts?

[Joun]

Re: LG L1953S doesn't power on

Yes,didn't find any..

[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

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..

[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

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.

[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?

[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.