LG 37LB1R lcd tv startup problems

[anno]

hi. problem with lg 37LB1R lcd tv. i changed power ic and some smd components near ic. now tv has power but problems with starting up. i also changed secundair capacitors , but didn't improve. Tv is starting up, led is flickering, then back off (relay clicking on/off) . The 12 volt is a little bit low, 11.4 volt. the 6 volt line is a little bit noisy (grass).

the current sense resistor was a little bit black because power ic blowed, but is measure exact the value it should be (i have esr/low ohms meter).

i don`t understand why the main power supply is going off. is it detecting the 12 volt line is to low or other error. i try heating the mainboard and power supply but doesn't help either.

i don`t know what to do now. maybe there is a mainboard problem

[anno]

Re: LG 37LB1R lcd tv startup problems

i don`t understand where the ripple is coming from. i replaced all caps with low-esr caps. what part can cause ripple too?

[newtothis]

Re: LG 37LB1R lcd tv startup problems

Have you tried disconnecting the PSU from the main and forcing the PSU on?

[anno]

Re: LG 37LB1R lcd tv startup problems

not yet. i can try. then i need to connect the 5v to the ps-on signal

[newtothis]

Re: LG 37LB1R lcd tv startup problems

not yet. i can try. then i need to connect the 5v to the ps-on signal

Yes using a 470hm to 1kohm resistor

[anno]

Re: LG 37LB1R lcd tv startup problems

i tested the psu stand alone and found out the 12v line is low (10.8v). i tried with 12v 0,5a lightbulb as load. there is 400 mA ac on the line. i replaced the caps in the 12v line, but didn`t improve. i am stuck at the moment. why there is ac ripple if the caps are good. i used low esr

[selldoor]

Re: LG 37LB1R lcd tv startup problems

What make series caps did you use and where did you buy them.

Check for leaky diodes

[anno]

Re: LG 37LB1R lcd tv startup problems

it is panasonic FC series. The diode is fch10a15 3 legs. is it a good idea to check this diode, out of circuit?

[selldoor]

Re: LG 37LB1R lcd tv startup problems

I really meant the black cylindrical ones - easier to lift one leg of them than wrestle with a 3 legged one. It is the reverse resistance that is important should be infinity. I have been wondering if you could test for ac voltage on each end but dont know if that is a valid test? I will have to resd it up.

[anno]

Re: LG 37LB1R lcd tv startup problems

maybe the PFC circuit doesn`t work. do you know what voltage should be on the big Cap? it's rated for 450volt .

[selldoor]

Re: LG 37LB1R lcd tv startup problems

Around 326vDC without pfc

370 to 400 vDC with pfc

[anno]

Re: LG 37LB1R lcd tv startup problems

ok. i have 335vDC so the PFC circuit is not working?
i think this tv has a PFC circuit because the 450V cap

ii think i found the PFC IC, marking is 5501A (FA5501A)?

[anno]

Re: LG 37LB1R lcd tv startup problems

The ic is getting power (12v). but i don`t see good output pulses to the gate of FET. maybe the PFC ic is defect

[anno]

Re: LG 37LB1R lcd tv startup problems

I changed the PFC IC and the tv is fixed now