6632L-0450A Philips LG inverter board problem

[BigPete]

Hi,

I'm Pete from New Zealand.

My Toshiba 42inch LCD tv has no picture. The ccfl bulb is not turning on.
I've already replaced the four 35v 680uF caps on both the master and slave board.
I've read a couple of posts on here.
Refering to this thread here: https://www.badcaps.net/forum/showth...light=BD9897FS post number 13, I found 2 extra grounded pins. Pins number 27 and 28 of this datasheet https://cdn.badcaps-static.com/pdfs/...97ffe28ccf.pdf which is the db9897fs chip.

Is it possible the little smds connected to the chip are to blame for the ground or is it a chip problem?

Also the resistance of one of the FETs is not the 8.5k (or in my case 8.29-8.33) it's supposed to be.
I tested the FETs on the main board using this website http://www.sentex.ca/~mec1995/gadgets/mostest.htm and they all passed.
I used this thread https://www.badcaps.net/forum/showth...FS+8.5k&page=2 last post, to figure out the FET resistance.

The problem is on the master inverter board.

Any insight would be much appreciated.

Cheers

Pete

[BigPete]

Re: 6632L-0450A Philips LG inverter board problem

I was just thinking, I noticed pins 27 and 28 are not used on the slave board. Could I swap them? Or could there be more internal problems with chip db9897fs other than the extra grounded pins?

[budm]

Re: 6632L-0450A Philips LG inverter board problem

Not sure how close these sch for the Master/Slave board will match your boards, but it may give you some ideas how the circuits work, these two sch are from the help of DAKOTAKID.
You do have 24VDC and the BL_ON signals, right?

[BigPete]

Re: 6632L-0450A Philips LG inverter board problem

Thanks for that Budm. These are slightly different. Pins 27 and 28 are definetely not used in the slave.
At least looking at the schematics, it could be possible that a capactitor or resistor has failed.
I do have 24.3vdc and the other signal is also on, I forget what voltage, 4.5 or 4.9 I think. Unless it's an overvoltage problem! I'll have to recheck otherwise.
I'll unsolder the 2 grounding ic pins to see if they are shorted internally. It'll at least rule out the rest of the circuit.

[BigPete]

Re: 6632L-0450A Philips LG inverter board problem

Unsoldering the IC pins was too hard so I unsoldered the resistors and capacitors in that circuit instead and those 2 IC pins were still grounding. Looks like I need to replace the chip.

[cadiman]

Re: 6632L-0450A Philips LG inverter board problem

Any L/G I have repaired with a master and a slave inverter was an au- optronics panel and the main problem was burned out ccfls bulbs taking out the master or slave inverter.

You will most likely have shorted mosfets. and bad ccfl bulbs 2 or more failed.

[BigPete]

Re: 6632L-0450A Philips LG inverter board problem

Mosfets are fine, though I haven't tested them with a load. How do I test the bulbs without an inverter? LCD shows a picture in the background, just dark. I suspect the slave is fine. Is there a way I can trick it into firing up the bulb?

[BigPete]

Re: 6632L-0450A Philips LG inverter board problem

Ok. I managed to seperate the 2 grounding pins on the IC. If I turned on the TV now, would it be disatrous?

[BigPete]

Re: 6632L-0450A Philips LG inverter board problem

I replaced the BD9897fs chip. It's not pretty but it seems to works.
What's happening now is: The blue led on the board turns on for a few seconds, it then turns off with still no back light.
I thought maybe the slave could be the cause, so I tested the BD9897fs chip on the inverter board again and came up with a earthed pin on pin 26, the power supply pin. Previously this pin wasn't earthed, but if I hold my leads on it, with the continuity test mode, the numbers go up on my DMM, then the beeping stops. If I swap my leads around, I can repeat this fault.
I tested the 2 mosfets in the circuit and they aren't letting the ground through. I removed pin 26 from the board to eliminate this as well.
I guessing that when the numbers go up on my DMM it's charging a capacitor?

Does this all sound right? or am I completely off the mark? Do I have to look for a shorted cap or something.

Here's the link budm posted up on the previous page on the slave inverter schematics https://www.badcaps.net/forum/attach...8&d=1342453464

Thanks

[PowerAmpFreak]

Re: 6632L-0450A Philips LG inverter board problem

Repaired several of TV's using the famous LG inverters. I choose to buy a pair of new boards since they were pretty cheap, and if you get hold of boards of V1.3 they have all the necessary modifications already done, and you don't need to rebuild the boards.

[BigPete]

Re: 6632L-0450A Philips LG inverter board problem

Are these boards interchangable, even if the part numbers aren't the same?