LG W2053TQ 2 seconds to black

[Maxmad]

Hello,

This monitor faces 2 seconds to black problem.
Image is still visible when direct light hit the screen, so the logic board seems to be ok for now.

--I have already checked the transformer. Both inputs and outputs ohms are ok. However I replaced it with a spare one. Problem persists.

--CCFL are also good. I checked all 4 of them one by one, and all together with another inverter. Everything fine.

--2 dual mode Mosfets are ok. Both measured and checked outside of the circuit.


--Capacitors are all also checked. One of them was faulty and replaced. All other are good both with their capacity and ESR value.



I focused on IC DT8211 Light Inverter drive.

Pulse at pin 7 is triangle and correct. It is on all the time when monitor is on.

Pulse at pin 8, 16 and 17 seems ok but is off when monitor turns black. Seems as normal behavior because if the pulse at pins 16-17 stays alive then the HV will work and so does the CCFL.

Some voltage at pins 1,6,18 is ok too.

I tried to isolate the feedback section of the IC. So i desoldered pins 10,11 as it seems at the photos. Stll the same 2 seconds to black problem.


Is there any way to check if the IC is wrong? I don't know what else to check... I only missed the SMD resistors and capasitors (SMD diodes are checked OK)...

Maybe there is something wrong with other power supply signals or probably the logic board? for example signals like ADIM, BDIM... any way to test them?

Any help will much be appreciated. This schematic seems to be very close to W2053TQ as for the inverter part.(page 23)

[budm]

Re: LG W2053TQ 2 seconds to black

Can you locate the BL_ON (or INVR_ON) pin to see if it still present when the screen black out? The 4 blue high voltage ballast caps checked out fine with no resistance leakage? Pin 2 is the ENABLE pin which is the BL_ON.
BTW, if you look at page 6, pin 9 is the protection pin, if that pin is allow to rise above 3V, the comparator output will go high and shut down the out put drive circuit, if some thing is wrong in the first 3 seconds the Prot will activate, the cap on the PROT pin set the time (see page 9). You can ground out pin 9 to see if it will stay on but you will not have any protection.
Just about every inverter circuit has 3-second detection so something bad happen in the 3 seconds window, it will shutdown.

[Davi.p]

Re: LG W2053TQ 2 seconds to black

ballast caps, the blue ones?

[Maxmad]

Re: LG W2053TQ 2 seconds to black

thank you all for your help.

I am back after almost a month waiting for a power supply board replacement.
After many troubleshooting I decided to replace the whole board since I found nothing wrong with the original.

Replace with a brand new board and faced the same problem: 2-sec to black.
I rechecked the CCFLs and found a very unusual situation:



According to the picture this is the right connection between male and female connectors of CCFLs. 2sec occurs with this connection.

Leaving connector D with the original CCFL 4 and using a spare CCFL to connector C makes the problem disappeared.
Same if leaving connector C with the original CCFL 3 and using a spare CCFL to connector D makes the problem disappeared again!
So seams that only if both 3 and 4 CCFLs are connected at the same time causes the problem.

Rearranging the CCFLs to the connector as below (pairs twisting):

A--->3
B--->4
C--->1
D--->2

Still 2 sec to black problem...

But after a twist between 3-4 :

A--->4
B--->3
C--->1
D--->2

Problem disappeared! I checked both male and female connectors for problems and found nothing.
2sec to black problem disappears only with the above combination without changing the original CCFLs...

Sounds very strange to me... Probably both 3-4 CCFLs are faulty, but why only this combination works?

[Maxmad]

Re: LG W2053TQ 2 seconds to black

just to close the thread:

the problem was a defected ccfl lamp.
the system was able to start only under certain ground circumstances.
so that's way sometimes everything worked fine and sometimes not.

hope this helps on a similar situation.