LG L1953S doesn't power on

[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

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..

[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?

[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

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

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

I have read somewhere that the PWM controller ic needs Vcc of about 15-20 volts..Mine has 9.8volts.
Does that indicates a problem or is it normal ?

[Joun]

Re: LG L1953S doesn't power on

No,didn't have that value in my drawer..Hopefully a friend will bring it to me tommorow.
Thank you for your interest..

[budm]

Re: LG L1953S doesn't power on

So you did replace the caps and still get the same problem?

[Joun]

Re: LG L1953S doesn't power on

Well I heat 0.47uF cap but nothing changed..The moment I plug it in I have up to 15volts at 12V point of connector and it is descending at a rate of 0.05V/sec(meaning in 10 seconds it has dropped about 0.5Volts)

[Joun]

Re: LG L1953S doesn't power on

OK, I will use hot air gun and post results..Thank you

[budm]

Re: LG L1953S doesn't power on

You can use 1uF for testing. You can also use the soldering iron to quickly heat up the cap (out off the board) to see if the ESR goes down.

[Joun]

Re: LG L1953S doesn't power on

No,since I have my lab at home and didn't want to wake up everyone by using hair dryer..
I also don't have another .47uF capacitor.I guess its value is quite critical so I can use only an exact replacement ,right?

[budm]

Re: LG L1953S doesn't power on

Well, I would replace those caps as I redlined. If you heat up the bad caps, the ESR will go down. Did you heat up the two caps to see if the voltages come back?

[Joun]

Re: LG L1953S doesn't power on

Well the bigger cap is OK( I don't remember its value and I'm away from it now)
The smaller has nominal value 0.47 uF /50V.I check it with my ESR meter and it says 0 uF( which I quess is normal, since it can check caps above 1 uF) but it has ESR 20 Ohm!
I looked at an ESR table and a 1uF/50V cap must have an ESR of 4.5Ohm..
So my cap has gone bad? Or it has too low value and meter can't check it properly?

P.S My other cap meter this one says 390nF so it has normal capacitance but what about high ESR?

[budm]

Re: LG L1953S doesn't power on

Please try this first: heat up these two caps with hair dryer to see if the PS will stay on (you can monitor the 12v line), remove and check the values of these two caps or replace them, these two caps are part of the kick start and self powered circuits for the SMPS IC.

[selldoor]

Re: LG L1953S doesn't power on

Pics could have been a bit sharper - try and get them as near 2mb as possible ,should look llike this one:https://www.badcaps.net/forum/attach...1&d=1290283049
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

[Joun]

Re: LG L1953S doesn't power on

Since 5v and 12v are generated by the same SMPS, it sounds like it turns on then it goes off. Do you hear any fainted ticking sound from the yellow transformer? And What DC voltage do you have on that large Main DC cap?

Maybe it turns on for half a second or something..
I don't hear any sound from the transformer.Main cap has its voltage OK about 330V DC(230 VAC in Greece )I have measure its ESR and capacitance, both are OK.
Well the thing is a have voltages everywhere on primary but nowhere on secondary if thats any help..That's why I'm thinking maybe the PWM controller is faulty( but my knowledge on SMPS is very limited so I'm possibly wrong).
Thank you all for your answers.

[Nocta]

Re: LG L1953S doesn't power on

The ceramic cap next to D107 seems burned to me.

Check also the transformer below the main cap, next to C102.

[budm]

Re: LG L1953S doesn't power on

Since 5v and 12v are generated by the same SMPS, it sounds like it turns on then it goes off. Do you hear any fainted ticking sound from the yellow transformer? And What DC voltage do you have on that large Main DC cap?