LG32LN4500 No Display, but Audio work

[kazia]

LG32LN4500 No Display, but Audio/sound work

TV powers on, Audio there, no pic or backlight.

got schematic for LGP32-13PL1 it's same power schematic at page 19.

measuring at P201

power on = 3v
drv on = 2.9v
PDIM = 1.1V
3.5V, 12V, 24V ALL good.

measuring at IC801

1. 2.3V 8. 5V
2. 12V 9. 0V
3. 0V 10. 2.2V
4. 0V 11. 1V
5. 0V 12. 0V
6. 3V 13. 0.6V
7. 0V 14. 0V

Problem with IC 801 or what...

thanks

[kazia]

Re: LG32LN4500 No Display, but Audio work

any one...

[kazia]

Re: LG32LN4500 No Display, but Audio work

update, change the ic 801, still same problem.

[RCA2000]

Re: LG32LN4500 No Display, but Audio work

LIKELY...you have one or more LED strips in the panel...with at LEAST one bad LED. On P-801..pin 1 and 7 See if at power on, maybe after a few seconds...You get a BURST..of at least 100-170V...at least for a few seconds. If it DOES...then drops after that...it is VERY likely an LED BL problem. Remember these are run in SERIES>..and if ONE opens....AL on that string go out. And if the sense ckt. detects an abnormal draw..OUT it goes...

We are seeing a WHOLE LOT of LED BL problems... they are FAR..FAR LESS reliable...than claimed.. It has been claimed here it is because they are NOT really using them correctly, overdriving them...not sinking them enough, etc. LIKELY TRUE

Just MORE evidence..that the 'ol CRT...will NEVER be even EQUALED...let alone surpassed..as a display device...as far as reliablilty, simplicity and longevity goes. PDP..DLP...LCOS..DILA...ALL have pretty much "had their shot" and FAILED.to do so...

[budm]

Re: LG32LN4500 No Display, but Audio work

Page 9 of the provided power supply SCH:
LED B+ 65.6V~86.9V 0.4A(0.380~0.420A) ± 5% -
So what do you get on the L+ pin of the LED connector, 33VDC?
33VDC (DD) is the feeding Voltage to the Boost converter to boost the Voltage up to around 90V for the LED strings.

[kazia]

Re: LG32LN4500 No Display, but Audio work

Page 9 of the provided power supply SCH:
LED B+ 65.6V~86.9V 0.4A(0.380~0.420A) ± 5% -
So what do you get on the L+ pin of the LED connector, 33VDC?
33VDC (DD) is the feeding Voltage to the Boost converter to boost the Voltage up to around 90V for the LED strings.

thanks for reply, on LED B+ it's fluctuation 10 - 18v.
my be it's something shorted inside lcd.

[budm]

Re: LG32LN4500 No Display, but Audio work

Disconnect the LED connector first and check the L+, if the booster circuit is not working then you will only see the feeding Voltage which will be 33V, you have to have that 33V at least, look at the diagram on where the 33V is generated from.
It is generated by the same power transformer (T101) that also generates the 24V and the 3.5V supplies.
You need to check that 33VDC (DD) source to see what you have.

[kazia]

Re: LG32LN4500 No Display, but Audio work

disconnect the connector, got same situation, measuring (LED B+ and LED -) its still fluctuation about 10 to 18v.
on caps 801 or LB801 a little fluctuation about 120 to 125v

[RCA2000]

Re: LG32LN4500 No Display, but Audio work

No... check the + connector to GROUND...and see what you get THEN.,

[kazia]

Re: LG32LN4500 No Display, but Audio work

No... check the + connector to GROUND...and see what you get THEN.,

+ connector to ground is same as c801 to ground fluctuation about 120 to 125v,
then what should I check next.

[budm]

Re: LG32LN4500 No Display, but Audio work

OK, so you were not using Gnd as the ref for your meter, since you are see over 100V that means the boost converter is working and you have open circuit in the LED strings.

[RCA2000]

Re: LG32LN4500 No Display, but Audio work

You need to "force on " the Backlights now. YOU will need a resistor of say 220 ohms or so. Take one end--connect it to ground. The other end connect it to other LED - pin of that connector Power up and watch for that resistor to get HOT fast--BUT if the BL is ok...it should light DO NOT...do this for more than a few seconds...just long enough to PROVE the BL.

[kazia]

Re: LG32LN4500 No Display, but Audio work

You need to "force on " the Backlights now. YOU will need a resistor of say 220 ohms or so. Take one end--connect it to ground. The other end connect it to other LED - pin of that connector Power up and watch for that resistor to get HOT fast--BUT if the BL is ok...it should light DO NOT...do this for more than a few seconds...just long enough to PROVE the BL.

confirm again, R220ohm connect to ground and LED (-) pin.
how about the connector should I connect it to.

[kazia]

Re: LG32LN4500 No Display, but Audio work

done, places 390 ohm resistor, the screen still dark, but it flashes after disconnected power cord.
and resistor not get hot.