42lg3000-za No Picture but got sound

[tom66]

Re: 42lg3000-za No Picture but got sound

Screen isn't lighting up - first conclusion is inverter, then main board - but that being said I know of some T-cons which synchronise the inverter and without the T-con they won't light up. Is there any cable going from the inverter to any board other than the PSU?

[Jahson]

Re: 42lg3000-za No Picture but got sound

With fat tab to the top on master inverter 3rd in top row reads 00.3, 4th on top row reads 00.3

bottom 3rd in row reads 00.3, 4th in row reads 00.3

Slave:

on the slave board opposite the fat tab the other lil connector the sticky label south of the label those 2 mosfet read 00.4 each

[tom66]

Re: 42lg3000-za No Picture but got sound

With fat tab to the top on master inverter 3rd in top row reads 00.3, 4th on top row reads 00.3

bottom 3rd in row reads 00.3, 4th in row reads 00.3

Slave:

on the slave board opposite the fat tab the other lil connector the sticky label south of the label those 2 mosfet read 00.4 each

This doesn't seem right - that indicates everything is shorted. Are you testing from the top tab to the right most pin? I'm not sure what to make of those readings, the fuse would normally blow with those shorts...

[Jahson]

Re: 42lg3000-za No Picture but got sound

This doesn't seem right - that indicates everything is shorted. Are you testing from the top tab to the right most pin? I'm not sure what to make of those readings, the fuse would normally blow with those shorts...

Yea the opposite end, as you said the gate leg is left, the side you read from, then you said the other leg which is the far right end leg.

[tom66]

Re: 42lg3000-za No Picture but got sound

Yea the opposite end, as you said the gate leg is left, the side you read from, then you said the other leg which is the far right end leg.

Yeah, that sounds right. It would seem the design of this inverter makes it appear like it is shorted.. Otherwise, the fuse would have blown with some fury. Usually MOSFETs short all pins at once due to internal breakdown, but since there are no gate-source shorts, I'm going to tentatively suggest they are okay.

Next check is the transformer secondary resistance. Check each pair I've marked on the 20k ohm range. You should measure the same for all four transformers (two on each) if they are good.

I have a 32" Toshiba (working) here with a similar master-slave arrangement. If the slave is unplugged, there is a brief flash from one side of the screen (maybe 100ms max) and it then goes out. If the master is unplugged the screen stays dark with no flashes on turn on. If you close all the curtains and make the room very dark, then turn the TV on, do you see the briefest of flashes from the screen?

Also, are there any other cables going from the inverters to any board other than the PSU?

[Jahson]

Re: 42lg3000-za No Picture but got sound

The ones marked in green

[Jahson]

Re: 42lg3000-za No Picture but got sound

I do the transformer test right now, yea theres a cable that runs up to the t-con top center i didnt take a pix, its connect to the (av-board)

[Jahson]

Re: 42lg3000-za No Picture but got sound

If ive done it correctly, they are reading 0.00 on all points master and slave

[tom66]

Re: 42lg3000-za No Picture but got sound

If ive done it correctly, they are reading 0.00 on all points master and slave

That doesn't seem right - does it measure the same without the CCFLs connected?

Since there's a "sync" cable the next step is to check the T-con fuse.

[selldoor]

Re: 42lg3000-za No Picture but got sound

There are a lot 0000s cropping up here - Fresh start - check meter is ok -
On Ohms 200 probes apart reading =? Probes Together =?
On vDC measure a battery v =?
Redo the mosfet tests Meter back on OHMS 200 One probe on big centre tab read across with other probe

..............pin L Stub Pin Pin R and post results
Q200
Q201 etc

Also on those boards are there components labelled CF201 CF201 etc
Tom any ideas on that odd board designation
http://tvpartsfixit.co.uk/Images/Parts/319.jpg


EDIT
Jahson On your slave can you check the 3 big capacitor joints cant tell much from the photo
but on the right hand one the trace looks all burnt?

[Jahson]

Re: 42lg3000-za No Picture but got sound

I'm going to retake the images

200 ohms probes apart = 1 to the left
200 ohms probes touching = 00.2

[Jahson]

Re: 42lg3000-za No Picture but got sound

on my slave inverter i see CF200, CF201,

[selldoor]

Re: 42lg3000-za No Picture but got sound

Wow what an improvement in the pics but still cant make out if the right hand cap on the slave board is ok. Can you test the resistance across the cap and see if there is conductivity to the next joint.

On the master the transformer looks a bit cooked - can you do pics of the backs of the boards.

[Jahson]

Re: 42lg3000-za No Picture but got sound

the 3rd cap i cleaned it up, seems ok.

set the meter to 200ohms and check that cap

[Jahson]

Re: 42lg3000-za No Picture but got sound

got a itchy head moment, i just checked all the caps they all reading 1 on the left?

either this meter aint working, or im doing somthing wrong,.

Touch probes its reads the resistance. 00.3
When i try the caps it reads 1 on left side

[Jahson]

Re: 42lg3000-za No Picture but got sound

Looking on the transformer legs is this correct cant get any clearer image.

On master inverter T1 leg 3 just connects to a pin coming out of transformer, then leg 5 & 6 are bridged to a pin coming out of tranformer.

On T2 leg 3 connected to pin coming out, then leg 5 & 6 looks like they aint touching but its a very very very tiny gap and looks like a blob of solder?

On T200 leg 4 connected to pin coming out, leg 6 connected to pin coming out but not connected to 5 looks strange,

T201 leg 3 & 4 bridged, leg 5 connected to pin coming out cant workout if it should be connected to leg 6 tho.

[vinceroger69]

Re: 42lg3000-za No Picture but got sound

in toms post number 65 have you tested the transformers as in his post ie set your meter to 20kohm then test the windings as he has indicated? as i cant see your results you need to test all 4 transformer and note readings down
you only need to put the test probes one on each of the pins indicated in red by tom

[selldoor]

Re: 42lg3000-za No Picture but got sound

As VR69 says it is the other end that we are interested in - I missed toms pic that is why I wanted the bottom of the boards to check where the secondaries were. Do test as in Toms post.
Also did you ever check the fuse on the tcon,

[Jahson]

Re: 42lg3000-za No Picture but got sound

Do i put it all back together then check?
Also use the probes on those points?

[vinceroger69]

Re: 42lg3000-za No Picture but got sound

no need to put set together just check the 4 transformers as posted one probe one each of the red marked points meter on 20k ohm setting writ down all results and then put the meter back to 200ohm setting and re test tcon fuse.
try red probe to left red mark and black probe to the right red mark test all 4 transformers the same way you cant realy go wrong then.