Samsung 930B re-capped, no backlight

[alexanna]

Re: Samsung 930B re-capped, no backlight

I am beginning to wonder if something may be wrong in the inverter section.
With the logic board unplugged providing 3.3 volts to the on off pin causes the back lamps to come on but they resemble a Florissant light with a defective ballast flickering rapidly.

[alexanna]

Re: Samsung 930B re-capped, no backlight

Out of curiosity, with the tail lamp connected, are the voltages on pins 3,4 and 6 of the DM0565R still steady?

I will need to check that just a little later dinner calls

[Mikeley]

Re: Samsung 930B re-capped, no backlight

What readings did you get for each regulator? Last questions for tonight, did you have boards back in the metal chassis frame with all screws back in when you had the logic board connected and powered with problem present?

Was the LCD and front panel also connected to the logic board at the time? Try with everything connected once more, if that was the case, remove the LCD panel connector, check 5V and 13V.

Reconnect and remove front panel, remeasure voltage in order to eliminate each of these.

[jetadm123]

Re: Samsung 930B re-capped, no backlight

I will need to check that just a little later dinner calls

Please disregard what I had asked for earlier. The bulb is drawing more current than the 13V output is capable of putting out, which accounts for the dim light.

[leperinc]

Re: Samsung 930B re-capped, no backlight

Alexanna, I looked at your pic of the underside of the power supply board and I'm assuming U202 and U203 have been replaced because they have no obvious burns on them, U203 doesn't look like it's soldered correctly (or it could be the lighting.. )

carry on...

update: still waiting for my parts

[alexanna]

Re: Samsung 930B re-capped, no backlight

Alexanna, I looked at your pic of the underside of the power supply board and I'm assuming U202 and U203 have been replaced because they have no obvious burns on them, U203 doesn't look like it's soldered correctly (or it could be the lighting.. )

carry on...

update: still waiting for my parts

The problem really looks to be in the inverter area.
I have removed the Fet with the questionable solder, those 4 pads are on the drain of the Fet and all 4 pads show continuity to each other. Any way I removed and reinstalled the FET so there are no globs.
Something is happening the problem is getting worse, now with the logic board disconnected, the Fet that I just installed got so hot it melted the solder of the board. I am not finding any of the pads shorted to ground.
I used some Fet's I Had in stock, They appear similar to me but the amperage is rated lower, I wonder if that could cause this problem?
http://search.digikey.com/scripts/Dk...=FDS8958ACT-ND

[Pyr0Beast]

Re: Samsung 930B re-capped, no backlight

Replace both fets ?

Lower converter frequency.

Dimm output.

I found out that 20W flourescent lamps eat more power as they age, going more towards 25W ...

[alexanna]

Re: Samsung 930B re-capped, no backlight

Replace both fets ?

Lower converter frequency.

Dimm output.

I found out that 20W flourescent lamps eat more power as they age, going more towards 25W ...

Both have been replaced,anybody have ideas on the replacments I used?

[alexanna]

Re: Samsung 930B re-capped, no backlight

The problem really looks to be in the inverter area.
I have removed the Fet with the questionable solder, those 4 pads are on the drain of the Fet and all 4 pads show continuity to each other. Any way I removed and reinstalled the FET so there are no globs.
Something is happening the problem is getting worse, now with the logic board disconnected, the Fet that I just installed got so hot it melted the solder of the board. I am not finding any of the pads shorted to ground.
I used some Fet's I Had in stock, They appear similar to me but the amperage is rated lower, I wonder if that could cause this problem?
http://search.digikey.com/scripts/Dk...=FDS8958ACT-ND

I going to call myself extremely lucky, I had a power supply from a Samsung 19W monitor that had a problem with the LCD panel, there are some noticeable differences with the circuitry. The mountings were the same and the pin voltages are the same on CN2.
And it's working, I would still like to figure what is wrong with the original INV/PS,But at least I can get it out of here and make room for another.
Al.

[Pyr0Beast]

Re: Samsung 930B re-capped, no backlight

I'd check both mosfets for both inverters. Would also check their driving transistors.

[leperinc]

Re: Samsung 930B re-capped, no backlight

The parts from China finally arrived! removing the dead chips was a bit easier than I expected. I didn't expect the chips to be glued to the board, however the chips were hot and the glue was fairly soft. Soldering the new ones on went well. We now have a backlight. It's alive! Another one saved from the landfill.

Jetadm123 and retiredcaps: thank you very much for your help with this. If you're ever in the Ottawa area I owe you a beverage of your choice!

[retiredcaps]

Re: Samsung 930B re-capped, no backlight

The parts from China finally arrived!

Glad the parts from China worked. I use ebay a lot for these types of purchases and have had good luck with it.

Good job on the repair.

[jetadm123]

Re: Samsung 930B re-capped, no backlight

Great work! Glad things worked out. It's too bad you had to go all the way out to china to get the parts!

[jamenlang]

Re: Samsung 930B re-capped, no backlight

I just inherited a 930b with this no backlight problem. I have attempted to repair LCD screens in the past by replacing NPN transistors, that worked for a few minutes. I would really like to be able to complete a repair and have the screen WORK, maybe with a little help I can get this screen working again. My power light is on solid, I thought that replacing the capacitors with a kit from ebay would fix this. I replaced every cap with matching spec'd caps except for the 450v 100µf, (the kit didn't come with one). I tested the caps to the best of my ability, put my multimeter leads on them and they charged up. The two IC's labeled u202 and u203 aren't melted or exploded. I don't see any burns on the board. I can provide any test results that I can take down with a multimeter if someone can suggest what to check first.

[Jasgriff]

Re: Samsung 930B re-capped, no backlight

Some really clear pictures of the top and bottom of both boards would be fantastic as this would allow us to guide you in the right direction.

When you say there is no backlight at all do you not even get a flash of backlight when you turn it on? Or does it come on for 2 seconds then go off?

Using a flash light on the screen you should be able to see a very faint image. Can you try this?

[jamenlang]

Re: Samsung 930B re-capped, no backlight

Some really clear pictures of the top and bottom of both boards would be fantastic as this would allow us to guide you in the right direction.

When you say there is no backlight at all do you not even get a flash of backlight when you turn it on? Or does it come on for 2 seconds then go off?

Using a flash light on the screen you should be able to see a very faint image. Can you try this?

The LCD part is working, i saw the windows logo when i hooked it up. the backlight does not come on at all.

[jamenlang]

Re: Samsung 930B re-capped, no backlight

additional pictures of the LCD driver board

[jetadm123]

Re: Samsung 930B re-capped, no backlight

The LCD part is working, i saw the windows logo when i hooked it up. the backlight does not come on at all.

See post #2 of this thread. Use the 200 ohm setting on your meter.

[jamenlang]

Re: Samsung 930B re-capped, no backlight

See post #2 of this thread. Use the 200 ohm setting on your meter.

Should i test these on the board or take them off? should i test it with power applied /turned on?

I disconnected the logic board and applied 3.3v to the on/off pin on CN2 and the backlights stayed off. does that rule out the logic board?

[jetadm123]

Re: Samsung 930B re-capped, no backlight

Should i test these on the board or take them off? should i test it with power applied /turned on?

I disconnected the logic board and applied 3.3v to the on/off pin on CN2 and the backlights stayed off. does that rule out the logic board?

NEVER take resistance readings with power on. For now, go ahead and test them on the board.