LG RZ-27LZ55 momentary backlight

[zx81]

Re: LG RZ-27LZ55 momentary backlight

OK, just make sure to give me the Voltage readings on those pins, thanks.

Hi Bud,

The connector is on the main board. Hopefully things will be a lot clearer with the high res pics I've linked to below.

Here are the DCV's
TV OFF
ST-12v = 12.36
ST-12v = 12.36
INV-BR = 0.001
INV-CTL = 0.001
PWR2 = 0.001
33v = 0.001
24v = 24.74
24v = 24.74

POWER ON
T-12v = 12.17
ST-12v = 12.17
INV-BR = 0.001
INV-CTL = 3.308
PWR2 = 3.167
33v = 34.60
24v = 24.81
24v = 24.81

Here is the link to some very high res pictures:

https://dl.dropboxusercontent.com/u/...Res%20Pics.zip

I turned the light off in the room and used a torch and I can see menus/overlays and static. Sound is also ok.

[budm]

Re: LG RZ-27LZ55 momentary backlight

OK, every thing are there correctly except the Backlights brightness control line.
So try removing just that INV-BR line female connector from the connector housing or cut the wire so you can splice it back together later on, then see if you will get the backlights without the INV-BR wire in place.

[zx81]

Re: LG RZ-27LZ55 momentary backlight

With the INV-BR removed still the same one sec and then black.

[budm]

Re: LG RZ-27LZ55 momentary backlight

OK, we need to try using 2K (1/4W or larger will be fine) resistor between the BRI and the ST 12V to see what happen next.
If it still does the same thing then we will have look at the inverter circuit next and possibly the lamps assembly.

[zx81]

Re: LG RZ-27LZ55 momentary backlight

Can I use 2 1k resistors in series ?

[zx81]

Re: LG RZ-27LZ55 momentary backlight

I tried 2 x 1k resistors in series between INV-BR and ST-12v with connector removed from the main board. No red standby light and nothing while turning the set on via the remote.

[budm]

Re: LG RZ-27LZ55 momentary backlight

You have to have the connector back in place but not the INV-BR wire to the main board to do the force brightness control.
Two 1K in series is fine.

[zx81]

Re: LG RZ-27LZ55 momentary backlight

You have to have the connector back in place but not the INV-BR wire to the main board to do the force brightness control.
Two 1K in series is fine.

Ok trying that now.

[zx81]

Re: LG RZ-27LZ55 momentary backlight

Still the same 1 second of backlight then black.

[budm]

Re: LG RZ-27LZ55 momentary backlight

We need to see the pictures of the Inverter board next.

[zx81]

Re: LG RZ-27LZ55 momentary backlight

Will I need to remove the PS and main board to get to the tcon. If I follow the lvds cables from the main board will they connect up to the tcon?

Also should I now re-install the cable that we removed temporaraly from the conector INV-BR?

I am getting picture and sound would this not eliminate the tcon from the equation?

Sorry for all the questions as you can see I have a lot to learn

[vinceroger69]

Re: LG RZ-27LZ55 momentary backlight

This is the board budm is looking for pictures from your sets its some times under a metal cover,
https://flattvparts.co.uk/lg-rz-27lz...b51f647e2beeeb

[zx81]

Re: LG RZ-27LZ55 momentary backlight

This is the board budm is looking for pictures from your sets its some times under a metal covering
https://flattvparts.co.uk/lg-rz-27lz...b51f647e2beeeb

Thanks.
I don't know why I must have miss read Buds post and thought he wanted to see the tcon. My inverter board is covered with a metal cover. I will remove the covering and post hi res pics tomorrow.

Thanks for all the help guys.

[budm]

Re: LG RZ-27LZ55 momentary backlight

Thanks.
I don't know why I must have miss read Buds post and thought he wanted to see the tcon. My inverter board is covered with a metal cover. I will remove the covering and post hi res pics tomorrow.

Thanks for all the help guys.

I made the typo and made the correction from T-CON to Inverter, don't know why I typed in T-CON, sorry about that, the inverter board is under the metal shield.

[zx81]

Re: LG RZ-27LZ55 momentary backlight

I made the typo and made the correction from T-CON to Inverter, don't know why I typed in T-CON, sorry about that, the inverter board is under the metal shield.

Will get back onto this tomorrow.

Thanks.

[budm]

Re: LG RZ-27LZ55 momentary backlight

Famous DARFON Inverter transformers and CMO board.
http://www.shopjimmy.com/cmo-27-1424...t-inverter.htm
Check the S1, S2 winding resistance of all the transformers, they should be within 3% from each others.
http://lcdparts.net/TransformerDetai...ProductID=2740

I would also replace those electrolytics caps, check all the fuses also.
Picture is provided by SHOPJIMMY

[zx81]

Re: LG RZ-27LZ55 momentary backlight

Here is a picture of my inverter board.

Checked all 3amp fuses all ok
Checked all diodes all ok
Tested all E caps they all show close to 402 microfarads and all have ESR 0.74ohms

Resistance between S1 and S2 (pins 4 & 5 of the transformers) all show 0.948kohms when meter set to auto range. Apart from the second transformer from the right which reads 1.965kohms. Resistance between S3 and S4 (pins 1 & 8 of the transformers) all show 0.948kohms. The primaries all read 0.4ohms apart from the first transformer on the right which reads 0.7ohms.

What can we conclude from this could it be the transformer?

Also could I somehow test the individual CFL's/lamps/?

[budm]

Re: LG RZ-27LZ55 momentary backlight

"Apart from the second transformer from the right which reads 1.965kohms" That is not good.

[zx81]

Re: LG RZ-27LZ55 momentary backlight

Best way to proceed Bud?

[zx81]

Re: LG RZ-27LZ55 momentary backlight

Replacement board or just try and get a transformer?