MODIS BackLight Repair

[BMWGUY]

Hello, I have repaired many MODIS CCFL back lights. The LT1786FCS Ic that controls current to the florescent inverter and the primary winding capacitor are the problem 99% of the time.

The LT1786FCS receives info via the mother board SM bus.
It then increases or decreases the current to the inverter.

The SMDIC03680TB00KQ00 capacitor is on primary winding.
If it is bad you can only get 1/2 the KV output needed.

I always replace both at the same time.

Here is a link to buy the Ic http://www.linear.com/product/LT1786F

Here is a link to buy the capacitor http://www.mouser.com/ProductDetail/...IbFyINUMQIo%3d

MODIS boards are soldered using re-flow method but these items can be replaced using low temp solder and a small electronics iron.

Be careful removing the old Ic, heat all legs until it easily lifts.
Do Not Pry It Loose! The printed board may peel up with the Ic.
No Fixin That!

I have attached a BMP of the circuit and a BMP to show locations.

If you are not comfortable removing and soldering the Ic, most electronic repair stores will do the work if you have the parts.
Hope this is helpful

[DerekLMartin]

What sort of symptoms do you get when these components fail. My modis screen turns on and I can adjust brightness but doesn't go all that bright. Would this be my problem??

[BMWGUY]

Backlight will usually adjust but only go to be about half the brightness with it adjusted up to full. I would try the cap first

[Bushytails]

The SMDIC03680TB00KQ00 is a 0.68uF capacitor, but the typical application in the LT1786FCS datasheet shows a 0.068uF. Did you paste the wrong part number, or are you finding the much larger capacitor to be the right replacement? I checked an older MODIS where the capacitor was labeled, and it's a 104K, or 0.1uF. A 0.1uF replacement looks like it's SMDIC03100TA00KQ00.

I need to get my 'scope out and actually diagnosis it before swapping parts, of course... I'm leaning slightly towards the ZDT1053 dual transistor based on the symptoms, but will look at the primary capacitor and control IC first based on your post. Backlight lights very dimly, and on just one end. Stays about the same brightness if you adjust the brightness settings, but goes off entirely if you set it to maximum brightness. Seen this set of symptoms before?

Thanks,
--Bushytails

[Bushytails]

'scoped mine, signal from the control chip looked good, but the royer converter waveforms looked like ****. Decided the cap was open, and sure enough, a new .1uf fixed it.

--Bushytails

[Dwayne209]

Got a modis that is bright when plugged in to wall power but goes dark on battery power. The unit stays on, the screen just goes dark. would this IC be my problem....

Thanks guys

[Dwayne209]

Fixed it.... it was the capacitor listed above. Swapped one from an old board I had lying around. Thanks guys

[DerekLMartin]

Can anyone confirm that the original post has the correct part number for the capacitor? I am about to purchase these parts to repair my screen but don't want to buy the wrong capacitor. I may have to tear mine apart and see if there is a part number on my old one.
Thanks
Derek

[BMWGUY]

The SMDIC03680TB00KQ00 0.68uF capacitor is the recommended part according to the manufacture of the IC driver chip. The diagram is from their site with notes added.

The Snap-On MODIS board uses SMDIC03100TA00KQ00 0.1uF capacitor.
I have used both and either works fine.
The SMDIC03100TA00KQ00 0.1uf capacitor is the correct direct replacment part and the best choice.

[matt_o_70]

Has anyone tried a LED backlight kit such as this:

https://www.ebay.com/itm/LED-Backlig...gAAOSwTM5YvMiT

Its not very cheap considering what it is but, I am just staring to look for replacement options and this was the first on I came across..