Samsung Syncmaster T240 Backlight/Inverter Failure

[retiredcaps]

Re: Samsung Syncmaster T240 Backlight/Inverter Failure

Also pay attention to post #26 and reference to mosfet U202 for shorts.

https://www.badcaps.net/forum/showpo...8&postcount=26

[Funkhauser]

Re: Samsung Syncmaster T240 Backlight/Inverter Failure

Thanks for all the help! My brain is mush from electronics all day so I will resume the testing tomorrow. Just one question, if there is a short in a mosfet, where would it be? Between the gate and the drain/source?

[alexanna]

Re: Samsung Syncmaster T240 Backlight/Inverter Failure

If U201 is the 16 pin IC on the back of the board could you let me know the number
It will give me something research tonight.
Al.

[Funkhauser]

Re: Samsung Syncmaster T240 Backlight/Inverter Failure

Ok, I can't refuse that offer!
U202 is 4506GEH
U201 displays: SEM2005
0817

Good luck!

[alexanna]

Re: Samsung Syncmaster T240 Backlight/Inverter Failure

If U201 is the 16 pin IC on the back of the board could you let me know the number
It will give me something research tonight.
Al.

Well I am unable to find it, maybe someone else can
Al.

[retiredcaps]

Re: Samsung Syncmaster T240 Backlight/Inverter Failure

Just one question, if there is a short in a mosfet, where would it be? Between the gate and the drain/source?

I test all 3 possibilities. S-G, S-D, G-D. Any reading under 30 ohms indicates a possible short.

[bonney]

Re: Samsung Syncmaster T240 Backlight/Inverter Failure

https://www.badcaps.net/forum/showpo...8&postcount=26
that is a good post to read

[alexanna]

Re: Samsung Syncmaster T240 Backlight/Inverter Failure

Ok. Your instincts were correct.
The adj dim is 0.8V on and 0 V off.
The on/off is 4.6V on and 0V off. However, if I switch the monitor off and on with the DMM lead attached to the pin it reads 0V. I can only get the 4.6V when I switch the monitor on and then read the pin voltage.

I think there have been some good ideas for things to check on your monitor
Retired caps suggested to check for the 15v getting to the 16 pin controller and that it has a ground.
I think it would be a good idea to check the voltage pin 11 as the monitor is powered on and off also, it looks like it's on off signal.
You will need very steady hands and possibly someone to help you power on and off the monitor
If you follow the single post link that retiredcaps provided, it gives the pin outs.
My reasoning on the problem you are having is there is no hint of back lights and the inverter fuse was good, I think it would be a good idea to see if the main board is asking for the back lights to be on. The problem I have is I don't know what voltage you would expect to see to expect to see on pin 11, maybe someone else will know
Al.

[Funkhauser]

Re: Samsung Syncmaster T240 Backlight/Inverter Failure

Ok people I am back for more!

I have found the pdf for the sem2005 16 pin chip which is attached to this post. After viewing the document I figured that there should be a min of 2.0 v on pin 11 when the monitor is turned on and a max of 1.0 V when it is off.

I have tested the chip, with the negative lead on the screw whole ground and found 3.4V when on and 0.0 V when off. Also, I found 15.57 V on the Vcc pin.

Looks like the chip is functioning, what do you guys think? I am nervous about testing the U202 MOSFET because I am unsure of how to do it.

EDIT: I checked the resistance of all the leads while the chip was in the board. I got nothing under 30 ohms between all the pins.

[alexanna]

Re: Samsung Syncmaster T240 Backlight/Inverter Failure

Ok people I am back for more!

I have found the pdf for the sem2005 16 pin chip which is attached to this post. After viewing the document I figured that there should be a min of 2.0 v on pin 11 when the monitor is turned on and a max of 1.0 V when it is off.

I have tested the chip, with the negative lead on the screw whole ground and found 3.4V when on and 0.0 V when off. Also, I found 15.57 V on the Vcc pin.

Looks like the chip is functioning, what do you guys think? I am nervous about testing the U202 MOSFET because I am unsure of how to do it.

I have gone as far as I dare take you with this.
Right now it would be a good idea to beg/ borrow or, well never mind. Try to get some high detail photos of the front and back of the inverter/PS. As close to the 2000x2000 max limit as possible.
Hopefully someone with more knowledge than I have will provide the steps to continue with.
Al.

[Funkhauser]

Re: Samsung Syncmaster T240 Backlight/Inverter Failure

Alright alexanna, I appreciate all the help! I will ask around for a good camera to snag some pictures. Right now I am eyeing this ebay auction as my last option.

However, I am sad to say that I damaged the monitor display screen last time I opened it up. It is on the far right of the screen so I hope it is still functional!

[alexanna]

Re: Samsung Syncmaster T240 Backlight/Inverter Failure

I realy don't think your to the point of having to purchace a power supply, it could be a $5.00 fix.
How bad is the LCD screen, what happend?
Al.

[Funkhauser]

Re: Samsung Syncmaster T240 Backlight/Inverter Failure

I put too much pressure on it while closing the casing and now there is a section about 1 inch square of what appears to be damaged pixels. It is hard to describe what it looks like, I held the screen in front of a light source and it looks like thick red horizontal and vertical lines.

Im pretty sure I have not damaged any of the controller board or ribbons so I think it is still in working condition.

[Funkhauser]

Re: Samsung Syncmaster T240 Backlight/Inverter Failure

Ok, I've found a camera and took some pictures of the top and bottom of the board. Let me know if the quality is alright.

[alexanna]

Re: Samsung Syncmaster T240 Backlight/Inverter Failure

The pictures could be better, Try using natural light on a sunny day by a window.
It sounds like The LCD panel is damaged; if you get the monitor working will you be happy with the display. I would think it would stick out like a sore thumb.
Ok I have to ask this, Is the inverter transformer melted, it doesn't look good in the picture
Al.

[Krankshaft]

Re: Samsung Syncmaster T240 Backlight/Inverter Failure

Secondary on the inverter transformer is shorted. Could have told you this 7 days ago if we had pics .

Unless you can find a replacement transformer further troubleshooting is meaningless.

This is the only source I know of for them:

http://www.lcdparts.net/T.aspx

Looks like that 5 lead surface mount component directly under the transformer (under H5302) contains all the primary drivers in one package. I'd get a datasheet and check the transistors inside it for shorts if you can find a replacement transformer.

Minor blackening on the end of the CCFLs is normal a bit of emissive substance sputters off the cathodes each time the lamps are powered up. Standard hot cathode florescents (used for interior lighting) blacken at the ends as well for the same reason.

[Funkhauser]

Re: Samsung Syncmaster T240 Backlight/Inverter Failure

Good catch!

It sounds like The LCD panel is damaged; if you get the monitor working will you be happy with the display. I would think it would stick out like a sore thumb.

To be honest, I just want to get this thing working! The damage is on the far side of the screen so it shouldn't be a problem. A cracked 24" is better than an old 17" crt!

Secondary on the inverter transformer is shorted. Could have told you this 7 days ago if we had pics .

Unless you can find a replacement transformer further troubleshooting is meaningless.

It is amazing that I overlooked the obvious melted transformer. There is a replacement here that I'm going to order. The part should arrive before Christmas so stay tuned!

Thanks again to all who have helped!

[retiredcaps]

Re: Samsung Syncmaster T240 Backlight/Inverter Failure

Secondary on the inverter transformer is shorted. Could have told you this 7 days ago if we had pics .

This is the exact point I'm trying to make with newbies in post #3.

For future newbies reading this, please post good clear focused pictures of your particular boards.

[Krankshaft]

Re: Samsung Syncmaster T240 Backlight/Inverter Failure

Check the driver transistor package too for shorted transistors that tabbed surface mount component mounted to that huge copper trace (heat sink).

[Funkhauser]

Re: Samsung Syncmaster T240 Backlight/Inverter Failure

Krankshaft, I am unsure about what component you are talking about. I have checked the 16 pin driver chip and the mosfet 5 pin, both of which are mounted on the bottom of the board.