52" Sharp LCD Transformer Backlight Bypass?

[Stan23]

Re: 52" Sharp LCD Transformer Backlight Bypass?

So has anyone confirmed the transformer part number on the master and slave inverter boards on this sharp TV?

[budm]

Re: 52" Sharp LCD Transformer Backlight Bypass?

http://www.youtube.com/watch?v=oE6K4xBVweA&feature=plcp
This is how it works:
The SONY and SAMSUNG uses the current sensing transformer, the primary is in series with the lamp, the secondary feeds the rectifier diode, the more the lamp draws the current the more output feedback on the secondary side will be fed back to the inverter board IC UI101 Isense pin 14, normal output from the sensing coil is 0.2VAC, it trips at 1.4VAC when lamp draws too much current.
As you can see in the diagram, there is no current sensing circuit on the MOSFET's (QI210, 202) that drive the Inverter HV transformer at all, the only protection it has is the FUSE 3.12A fuse, if one lamp draw too much, it will not be enough to blow the fuse, it will not be a good design of the circuit cannot detect one bad lamp, that is why eash lamp is connected to the individual current sensing transformer.
The other sensing circuit for open lamp connection/ or lamp not drawing current after firing up turn on sequence, done by dual diode di101 (you can see them on teiny's inverter board).
I did not have a chance to probe and analyze the LD pin and the rest of the board yet, it is also used for OV protection.
The inverter circuit has to be able to detectdown to one lamp overcurrent draw, it cannot use just the fuse to protect the MOSFET's since one lamp draw too much current will not be enough to blow hi amp fuse, but the wiring for the lamp can badly burnt up so it must have a way to detect lamp current correctly.
So inverter board needs to have detection circuits to:
1) If the lamp connector is not in place, it will have to shutdown the circuit otherwise you will get nice big arcing at the connector.
2) Ability to detect the current draw of the bad lamp.
3) Ability to detect that after the high kick start voltage is applied to the lamp, the lamp will stay conducting after fired up.

[tom66]

Re: 52" Sharp LCD Transformer Backlight Bypass?

You cannot remove the signal feeding that detection circuit which is on the return side of the lamp, the circuit is looking to see if the lamp is conducting and how much, when you cut the trace or remove the cap, there will be not output signals that goes back to the PWM IC to tell if the lamps are on or not. The primary side of the transformers are connected in parallel, there are duplicated detector circuits for each set of lamps, we just need to find out what the feedback signal level should be to satisfy the PWM feedback signal requirement. I will have to trace out the connection to see how they are connected, or we can disable the PWM dection input. I do not see any PWM IC on this master inverter board.
Also, is there a slave inverter board?
Also the resistance reading of the suspected transformer has the same resistance reading as the good transformer?

I was going by the Norcal video where that tracei is only used for the open built detect; it picks up the high open circuit voltage. Short circuit is done by primary current sensing, or the fuse.

[Cosmo66]

Re: 52" Sharp LCD Transformer Backlight Bypass?

Whats the part number on the transformer?

Is it Z1335 07086

oh nevermind I can see in the picture they are different than the ones I have here

[tieny]

Re: 52" Sharp LCD Transformer Backlight Bypass?

I see, I thought each transformer just drove their corresponding lamp. So a transformers from both the master and slave actually drive one lamp?

Anyway I had already ordered the inverter board yesterday though. =)

Welcome back! I haven't see you around the forum much lately budm.

[budm]

Re: 52" Sharp LCD Transformer Backlight Bypass?

By passing the circuits will be hard since both boards have sensing circuit, the Master and Slave lamp drive work in concert, one push one pull (those small inverter transformers can not drive the tube that long by using one transformer, that is why they use MASTER/SLAVE SETUP), so you will also have to stop the transformers that drive the lamp on both side (Master side and Slave side). Not sure how to get that done yet.

[tieny]

Re: 52" Sharp LCD Transformer Backlight Bypass?

At first I switched two transformers on the master board to see the ccfl changes. Then I switched the bad one from the master onto the slave, so now the bad transformer is on the slave, the one where the cap was removed. (just making sure the test was conclusive)

[budm]

Re: 52" Sharp LCD Transformer Backlight Bypass?

So you switched the transformer on the Master or on the Slave board?

[tieny]

Re: 52" Sharp LCD Transformer Backlight Bypass?

Yes both boards have transformers on them, heres a photo of the front of both boards

[budm]

Re: 52" Sharp LCD Transformer Backlight Bypass?

I am a little confused, so the Master and the Slave inverter boards are about the same setup? So the both Master and Slave have transformers?

[tieny]

Re: 52" Sharp LCD Transformer Backlight Bypass?

Oh oops, I keep swapping boards and kind of got confused and just took a photo of the board I had out last thinking the circuit was the same.

Heres the back of the master inverter board. I kind of striped some traces when desoldering the transformer... I'm thinking its the ground pins for the transformer?

[budm]

Re: 52" Sharp LCD Transformer Backlight Bypass?

But it has MASTER printed on the top left of the board as shown on the pictures in post 1.

[tieny]

Re: 52" Sharp LCD Transformer Backlight Bypass?

The photo I took was the slave inverter board. And yes the suspected transformer has the same resistance reading as the others at least I think. (Since I'm measuring the transformers pins and keep getting "1" on my meter on the highest range.)

[budm]

Re: 52" Sharp LCD Transformer Backlight Bypass?

You cannot remove the signal feeding that detection circuit which is on the return side of the lamp, the circuit is looking to see if the lamp is conducting and how much, when you cut the trace or remove the cap, there will be not output signals that goes back to the PWM IC to tell if the lamps are on or not. The primary side of the transformers are connected in parallel, there are duplicated detector circuits for each set of lamps, we just need to find out what the feedback signal level should be to satisfy the PWM feedback signal requirement. I will have to trace out the connection to see how they are connected, or we can disable the PWM dection input. I do not see any PWM IC on this master inverter board.
Also, is there a slave inverter board?
Also the resistance reading of the suspected transformer has the same resistance reading as the good transformer?

[tieny]

Re: 52" Sharp LCD Transformer Backlight Bypass?

I just removed the cap and plugged it in but there was no change.

In the picture where i circled the bad transformer that I removed, so I should cut that trace? (the red line)

[tom66]

Re: 52" Sharp LCD Transformer Backlight Bypass?

Cutting the trace is easier. Just use a knife or screwdriver to break it and check it with a multimeter. Leave the cap there in case you later decide to replace the transformer or find it's not the fault.

[tieny]

Re: 52" Sharp LCD Transformer Backlight Bypass?

When you say cut, do you mean cut the trace to open circuit? Would removing the ballast cap also give the same results?

[tom66]

Re: 52" Sharp LCD Transformer Backlight Bypass?

I think that this should disable the shut down feature for that transformer.

[tieny]

Re: 52" Sharp LCD Transformer Backlight Bypass?

Here you go

[budm]

Re: 52" Sharp LCD Transformer Backlight Bypass?

Can I see the picture of the whole bottom side of the inverter board?
This is not the same setup used in the SONY/SAMSUNG balancer board, the transformers on the balancer is used for detecting if the lamp is drawing current or not, when the lamp is bad then there will be no voltage feedback to the PWM IC so it will shutdown the circuits.
Your board use the typical sensing setup as you can see the pin of the output side is fed in to the sensing circuits.