LG 42LB5DF No Pic No Sound

[mmartell]

When connected to mains power light flashes for some time then stays lit. Some time after that I hear a relay click and I am then able to power it on with the button on the panel. Voltages at the power supply connectors as follows:

ACD / 5v
PWR ON / 3.3v
5Vs / 5v
I-C / 3.3v
ERR / 0v
BRI / 5v
DIM / 1.7v
6V / 6v
3.4vON / 1.9v

All other voltages are present as follows (stated/actual) :

19V / 18.5v
6V / 6v
3.4V / 3.4v
12V / 11.8v
24V / 24.2v

At this point the power button is unresponsive.

What to check next ?

[mmartell]

Re: LG 42LB5DF No Pic No Sound

The pin labelled "ERR" is labelled in the SM as "5V Det/Error Out" and also "5V_MNT" and despite the name is designated an INPUT.

Is this the pin which goes high to tell the PS to produce the 5V rail for the main board because not only does it read 0V I don't see where the 5V output pin is to measure it ?

[budm]

Re: LG 42LB5DF No Pic No Sound

Right now the main is getting correct voltage to run otherwise it will not put out PS_ON to turn on the 12v/24v power supply.
Can we see the pictures of the boards?

[mmartell]

Re: LG 42LB5DF No Pic No Sound

Not at home atm will post them tomorrow...

Where is this VA/VS supply voltage I see mentioned ? I don't see it marked on the PS board.

[budm]

Re: LG 42LB5DF No Pic No Sound

"Where is this VA/VS supply voltage I see mentioned ?" This is LCD TV not Plasma TV.

[mmartell]

Re: LG 42LB5DF No Pic No Sound

Got it.

[mmartell]

Re: LG 42LB5DF No Pic No Sound

Here's a pic of the topside power supply board. I don't see any bulging capacitors or anything else amiss.

[budm]

Re: LG 42LB5DF No Pic No Sound

OK, pictures of the inverter board? The whole back side of the TV so we can see what we are dealing with. Any labels on the connectors of the Inverter board will help also.

[mmartell]

Re: LG 42LB5DF No Pic No Sound

Ok cool, I had the main board out but had since put it back in with the shield on hence no pic of that.

Umm... the inverter board is (are) the boards to the far left and right ?

[budm]

Re: LG 42LB5DF No Pic No Sound

I cannot tell until I can see the whole back side of the TV, it may have one or may be two inverter boards.

[mmartell]

Re: LG 42LB5DF No Pic No Sound

Ok will get pics up soon.

[mmartell]

Re: LG 42LB5DF No Pic No Sound

The four caps each on Master and on Slave pass a visual inspection. They read in the range of 6000uf (in parallel ?) But their esr is extremely low.

[mmartell]

Re: LG 42LB5DF No Pic No Sound

Forgot to attach pics...

[budm]

Re: LG 42LB5DF No Pic No Sound

OK, CMO inverter boards, check ALL the fuse, including this tiny F5 one that looks like resistor in this example.

[mmartell]

Re: LG 42LB5DF No Pic No Sound

I tested the four fuses as shown between the capacitors on both boards and they tested for continuity. Should I test for voltage on both sides of the fuse instead ?

[budm]

Re: LG 42LB5DF No Pic No Sound

Yes. By the way, you said 4 fuses, two on each board? The board also has the small black fuses as shown on post14
http://www.shopjimmy.com/philips-996...verter-kit.htm

[mmartell]

Re: LG 42LB5DF No Pic No Sound

I'm going to remove one of these boards then to have a closer look under my magnifier to locate that fuse then reinstall and test for voltages at the fuses.

[mmartell]

Re: LG 42LB5DF No Pic No Sound

Located the smaller fuse on the Master inverter - did not find a similar one on the Slave.

Tested the Master Inverter and found 24.2v before AND after all three fuses. I notice there is a TCON connector to the Master inverter, any way to test that ?

[mmartell]

Re: LG 42LB5DF No Pic No Sound

Tested the Slave Inverter and found 24.2v before AND after the two fuses.

What kind of voltage is running to the panel through the edge connectors on the Inverters ? If the panel itself was broken would that shut down the power supply or not ?

[mmartell]

Re: LG 42LB5DF No Pic No Sound

I have to apologize, Bud ! I just realized I've been stating the facts wrong.

Although I have no pic, more precisely I have no backlight !

Also where I stated I have no sound I can't say for sure as I haven't connected a source because I can't tell which input I'm on anyhow (as I have no OSD and no remote control)

Now...

I have 24v to other side of fuses on both inverter boards...
I have 3.3v on I-C pin which is the Backlight_ON control...
yet I still have no backlight.

q. Can the TCon board keep the backlight from turning on ? If so can the set be turned on with that board disconnected from the inverter ?

q. Is it possible to measure the output of the inverter to see if there is voltage (HIGH VOLTAGE!) ? Obviously if there is voltage at the output I could conclude the panel (backlight) has failed.