LG 32 lcd not always turning ON

[nathaniel]

hello everyone

my lcd started to make trouble turning ON .
it goes on once a while mainly when i plug out the ac and let it sit for acouple of hours.

when it's not turning ON the led acts normally (blinks a few time red then solid blue) just display or sound wont .

it a 32LG32R

can you please help me out here

thank you for your time !

[CapLeaker]

Re: LG 32 lcd not always turning ON

verify PSon voltage in both conditions. If you don't get PSon signal from the mainboard, then there is trouble there.

[nathaniel]

Re: LG 32 lcd not always turning ON

hi
thanks for the quick reply
i just tested what i think is PSON
i get 1.5v when on 0v when off (while still dont have picture)

is it ok?

[victor_cj]

Re: LG 32 lcd not always turning ON

Check 12V, 16,5V, 25,2V when PSon is 1,5V. Check at C609 PFC status.

[CapLeaker]

Re: LG 32 lcd not always turning ON

hi
thanks for the quick reply
i just tested what i think is PSON
i get 1.5v when on 0v when off (while still dont have picture)

is it ok?

So what is the PSon voltage if there is a picture? To me, the PSon voltage is low. But any how, when the TV is turned on, check all the power rails. See if one or all voltage rails are there or missing.

[newtothis]

Re: LG 32 lcd not always turning ON

Yes PS_ON should be >2.5v to start the set.

Can you confirm how you are testing and also your meter battery please

[nathaniel]

Re: LG 32 lcd not always turning ON

i'm get this resaults:

1.5v - power_on
5.2v- to logic board
no 16.5v to " "
no 12v " " "
no 24v " inverter board

i hope i get lucky tomorrow so i can test and compare
when it does go on.

victor sorry i don't know what PFC status mean or how to test it.

*excuse me for my poor knowlege in electronics , but i'm learning quickly
thank you all for your patience

[newtothis]

Re: LG 32 lcd not always turning ON

Voltage at main filter cap (The big cap rated 450v) .. Red to + and Black to - : Meter at 600VDC. Careful as working on HOT side of the board.

What reading do you get when attempting to power the set on?

[saddle_au]

Re: LG 32 lcd not always turning ON

If you have replaced the caps on the secondary side of the P/S, I'd check the values of the capacitors around the regulators on the mainboard. Also the two diodes around the switcher, D1100 and D1102.

I've seen the mainboard sit and play dumb when the standby circuits could not startup the main processor because of odd waves coming out of the mainboard switchers. Leaky blocking diodes caused the voltage wave to rise but then fall back again, unsuccessful starting the switch mode off. Cooling the parts with freeze spray identified the faulty circuit area (lowered the threshold to maintain pulsing), but not the exact parts.

[nathaniel]

Re: LG 32 lcd not always turning ON

update:
the set turned on today and i get this readings:

power_on is 1.5v as when not turning on
but then i get all the other 12v , 16.5v and 24v

at the big caps i get 329v when on and 310v when off

is the problem in the power board ?

* i do not have a capacitance test on my multimeter

[newtothis]

Re: LG 32 lcd not always turning ON

update:
the set turned on today and i get this readings:

power_on is 1.5v as when not turning on
but then i get all the other 12v , 16.5v and 24v

at the big caps i get 329v when on and 310v when off

is the problem in the power board ?

* i do not have a capacitance test on my multimeter

329v when all other voltages are present?

If so please change your meter battery, I think its bad.

PS_ON should be higher than 1.5v and the PFC cap should be >360 when 12v etc are present

[nathaniel]

Re: LG 32 lcd not always turning ON

i believe the battery is fine (i normally get a battery icon when low)

i tested with another one i got - the cap read 333v and 1.52v at power_on

* this is the equipment i've got:

[CapLeaker]

Re: LG 32 lcd not always turning ON

I am still not convinced that 1.5v on PSon is correct.
I'd disconnect the main board from the PSU and "force" the PSU on. Check if all the rails come up on the PSU.
Usually it is done by using a 1k ohm resistor from STBY to PSon and another one from STBY to BLon (backlight). As soon as you plug it in, the backlight should be on and all the voltage rails should be on as well.

Also the 330V on the filter cap is low. Should be more than 360V. Not sure if you meter is good or not...

[vinceroger69]

Re: LG 32 lcd not always turning ON

whats the power board model number? maybe theres a schematic about

[newtothis]

Re: LG 32 lcd not always turning ON

Can you take a picture of what setting you are testing on the meter please

[victor_cj]

Re: LG 32 lcd not always turning ON

i believe the battery is fine (i normally get a battery icon when low)

i tested with another one i got - the cap read 333v and 1.52v at power_on

* this is the equipment i've got:

You must have 385-400V, PFC working bad in this case.

[victor_cj]

Re: LG 32 lcd not always turning ON

victor sorry i don't know what PFC status mean or how to test it.

PFC ON mean 385-400V at C609
PFC OFF mean 290-315V at C609
PFC working bad mean 316-384V at C609

[newtothis]

Re: LG 32 lcd not always turning ON

You must have 385-400V, PFC working bad in this case.

The set wouldn't start at 1.5v though and I would be surprised if he had 12v and 24v if the PFC cap did indeed only have 330v

[newtothis]

Re: LG 32 lcd not always turning ON

PFC ON mean 385-400V at C609
PFC OFF mean 290-315V at C609
PFC working bad mean 316-384V at C609

PFC will work at >360v

[victor_cj]

Re: LG 32 lcd not always turning ON

The set wouldn't start at 1.5v though and I would be surprised if he had 12v and 24v if the PFC cap did indeed only have 330v

This model have 1,2-2,7V PSon.