LG L196WTQ no power

[escape]

LG L196WTQ Dead

It shows no sign of power.
No powerled and no backlight flash, as if there isn't any power connected at all.

It's been like this once before - Thanks to this site (https://www.badcaps.net/forum/showthread.php?t=17123 ) I recapped some bulging caps it and it worked wonders for 2 years.
Now it's back again: This time I recapped every single cap on PSU and video board, even the big cap. Sadly this didn't work.

So now I humbly request some help digging further into the problem


Tests so far:
- Measured 330v on main cap
- Fuse is alright
- Measured the 5v and 12v pins from the PSU board to the video controller board: Ok (But I don't thrust that since it did so on the first recap aswell.)
- The power button have 5v going into it and when pressing you can clearly hear that the high pitch frequency noise from the psu changes slightly for a second. Just not enough to power on I guess.
- The black zener diods at D101 and D102 measures ok

Pictures:
Front PSU
Back PSU

Any tips on how to progress would be much appreciated.

[budm]

Re: LG L196WTQ no power

OK, since you do have 5V for the logic and the 12V for inverter and Logic circuit then your power supply is OK. So we need to check the DC Voltage on that connector P201 'ON' pin which is the backlights On COMMAND signal from the logic board, you must have the monitor connected to running PC otherwise the monitor will be in standby mode. When monitor is not in stanby, the ON pin should be >2VDC. If the ON signal is OK, then we need to dig deeper into the inverter circuit, it is important to know for sure if none of the lamps flash on or not, that will give us another clue.

[escape]

Re: LG L196WTQ no power

Thanks for quick reply.
With computer connected I get 0.79 V on that pin, I tested with stationary and laptop just to be sure. Had it connected through DVI if that matters.

Still nothing from power on LED or any flash on screen (Wasnt easy to set it up though )


Edit:
So if the PSU is ok, then the problem might be in video controller.
I googled and found the service manual:
video controller: http://tejpbit.se/temp/upload/Video_controller.png
Error checking: http://tejpbit.se/temp/upload/video_...r_no_power.png

Error checking number 1, 2, 3 checksout fine - But don't know how to test the crystal, just got a multimeter.

[budm]

Re: LG L196WTQ no power

"Still nothing from power on LED" Sinc the 5VDC feeding the logic board is present, so deeper checking on the logic board is next. There should be some 3-pin Voltage regulator ICs on the board that step the 5V down to 3.3V or 1.8V to run the processor.

[escape]

Re: LG L196WTQ no power

Let me get a new picture:Logic board (ignore the badly installed cap )
The schematics from google as posted earlier.

checked u901 and u902 and get 3.3v and 1.8v on the output pins = ok

Hmm, do I smell main chip failure

[selldoor]

Re: LG L196WTQ no power

Please can you upload pictures /files using manage attachments otherwise they disappear.
Thread then makes no sense and are lost to future enquirers

[escape]

Re: LG L196WTQ no power

Done.

[budm]

Re: LG L196WTQ no power

That is just the PCB lay out, not the the schematic diagram of the logic board.

[stj]

Re: LG L196WTQ no power

resolder D102

[budm]

Re: LG L196WTQ no power

D102 on the power supply/Inverter board? That Diode is used for rectifying the aux winding of the SMPS transformer for running the SMPS IC U101 which is filtered by startup/running cap C109. He is getting steady 5V and 12V.

[escape]

Re: LG L196WTQ no power

Hi.

I'm gratefull for every feedback possible. It's a cheap screen, but a good 2ms screen. I really want to keep it.

On psu:
Resolderd D102
Also diod testing gave beep on ZD101, but removing one pin and retesting proved it was alright.


I did another test: I took a 3v cell battery and connected it to gnd and the on pin at P201 (pin 9) and sure enough: The lcd backlight goes on perfectly and keeps on as long as the battery is connected. Nothing on screen and the poweron led is still dead even with computer connected.

I also rechecked the voltage going to the logicboard on p201, since I recalled I checked with logicboard disconnected.
With the logic board disconnected I get the 12v and 5v.
If it's connected I get 19v - cause for concern? 5v is still on 5v


Also for others that might need it:
Link to service manual: (Don't know if it's ok to have it hosted on badcaps, so will only be link.) - After 30 sec a small link will apear bellow the preview; "Get manual".

[stj]

Re: LG L196WTQ no power

D102 on the power supply/Inverter board? That Diode is used for rectifying the aux winding of the SMPS transformer for running the SMPS IC U101 which is filtered by startup/running cap C109. He is getting steady 5V and 12V.

regardless,
d102 had a really bad joint at one end!

that's why i study foto's.

[selldoor]

Re: LG L196WTQ no power

If you have it you can upload it again using manage attachments. It is better
for us as I guess most of us are limited to 2 downloads a day from that source.

[stj]

Re: LG L196WTQ no power

manual for badcaps server.

[selldoor]

Re: LG L196WTQ no power

Hi

Hi.

I did another test: I took a 3v cell battery and connected it to gnd and the on pin at P201 (pin 9) and sure enough: The lcd backlight goes on perfectly and keeps on as long as the battery is connected. Nothing on screen and the poweron led is still dead even with computer connected.


Was this with the logic/main board disconnected?


I also rechecked the voltage going to the logicboard on p201, since I recalled I checked with logicboard disconnected.
With the logic board disconnected I get the 12v and 5v.
If it's connected I get 19v - cause for concern? 5v is still on 5v

The 5v is regulated it is fairly normal for the 12v to rise if the backlights are not lit

Logic board needs more attention as budm says.

[selldoor]

Re: LG L196WTQ no power

Can we have a good picture of the bottom of the logic board to try and trace
the blon circuit.
Have you tried with it all connected up but with the lvds lead unplugged at the logic board end.
Sorry for the multiple posts - I keep getting distracted then think of something else.

[escape]

Re: LG L196WTQ no power

Hi.
- The cellbattery test was with the logicboard connected.

- "test with lvds lead unplugged at the logic board end": Don't know the term, but I did test to disconnect the "data cable" to see if I get power then (The big flat one that goes into the lcd - see picture): No difference.


- I tryed to take improved pictures of the logic board as per attachments. (Also somewhat fixed the badly installed cap )

[selldoor]

Re: LG L196WTQ no power

I cant trace anything much on that board - there is mention of the invon from the U501 Main processor in the manual pin 109? but cant see any diagram.
Other think it does mention is 1.8v can you test the power regulator that
produces the 1.8 from 5v U701? or U702?

[escape]

Re: LG L196WTQ no power

Looks like U701/U702 are eeproms: http://pdf1.alldatasheet.com/datashe...C02RMN6TP.html

The voltage regulators U901 and U902 - both reads ok (3.3v and 1.8v)

I also checked the voltage feed to the main chip: U501 pin 114 and 21 - Both ok (3.3v and 1.8v) so it's getting the voltage it needs to run I think.

u501 pin 109 (Gpid_p25 - INV ON (2) reads 3.3v

[selldoor]

Re: LG L196WTQ no power

Sorry I see you did all that before with budm
ok so need to track from T501 pin 109 to pin 9 on the connector