3G Backlight Circuit Explained at last
 

The attached pictures should help explain the backlight circuit of the 3G phone. The schematics are from the NXP Power Controller user manual - link to it here:

http://people.openmoko.org/tony_tu/G...50633DS_02.pdf

Many thanks to NXP for releasing it to the public.

The iPhone backlight circuit would seem to be a mix between Fig. 30 and 32 - there appear to be a component (I labelled it FET?) that combines at least one FET and possibly a second FET or diode.

I don't have the connections to the NXP power control chip shown on the board layout, but the schematics give the pin designations, and the NXP user manual gives the pin numbers. The word "GND" denotes a ground connection (it's hard to read text on the jpg image).

This contradicts the postings from Sassaki, but I have checked my board layout carefully.

Hopefully this will help everyone with 3G backlight problems be able to trace the source.

I can't get manage attachments to upload the images, so I have used links to them, if they aren't clear or working let me know:

http://loadmypic.com/server1/out.php...GBacklight.jpg
http://loadmypic.com/server1/out.php/i65621_Sch1.jpg
http://loadmypic.com/server1/out.php/i65622_Sch2.jpg

big thanks for ths PDF ...


BR / TA@UFIK




BY / QUICK - MOBILE

I traced down this on two different 3gs's with no backlights.
I have a couple questions for the smarter than me guys.
Looking at the Pict. with the backlight paths.... from this post
should there be any continuity across the yellow rectangular
thing that feeds the #2 pin on the connector?
And on both of my phones the smaller version of that below the coil....
i have no continuity from the left side to the coil above it.
But i do from the right side of it. And again theres no continuity across the little block its self.

1. Is there supposed to be continunity across the yellow rectangular pieces?

Thanks
tony

I will assume you mean 3G phones, this is not for 3GS phones.

There should not be continuity across the yellow rectangle that feeds pin 2 of the connector. This part is a capacitor. Same with the smaller yellow one below the coil - this is also a capacitor - no continuity across it. There should be continuity from the left side to the coil in photo as shown to the coil. The coil should show as having continuity between the left and right side. The right side of the small capacitor should be continuity to ground.

OK so it seems that there is no continunity from the left side of the small capaciter to the coil.
So if i create a jumper betwen them it should complete the circut.
Or is there a problem with no power making it to the left side of the capaciter.

Thanks for your help

Tony

Anybody got any input on this?
I would really like to get these thre units up and running.

Thanks
tony

Ooops, look like I was wrong about the connection of the coil and the small capacitor. It is the right side of the small capacitor that connects to the coil, and the left side of the small capacitor should be connected to ground.

I'll have to update the drawing.

OK
Then i have complete conectivity completly both legs.

The part in the middle you labeled FET there is a JLJ on it with a dot above the first J and under the L.
So if the paths are right, the coil is fine, where do we go from here.

Thanks
Tony

If you've check both legs out to the connector block, and you know the LCD module is good, then the thing I labelled FET, or the PMU chip must be the fault.

As I said I don't really know what the FET part is, if you can, take one from a spare motherboard and see if that fixes the problem. At least it's an easier to change part than the PMU, but if that doesn't work, then that leaves the PMU chip.

The other simple thing is to make sure you've tried holding the power and home button both on together for 10 seconds. This does something to reset the LCD when it won't come on.

There are coils on all phones that use high voltage (13v 17v) to light the led's of lcd .

True

But there is not a coil on the 3g that goes bad causing the "no backlight"
problem.

If you know how to fix the problem on the 3g please let us know.

Coil in 3G
 

Do you mean the coil on 3G in following Image isn't the problem?

http://forum.gsmhosting.com/vbb/atta...1&d=1287522699

Upload pic again?
 

Please, jseraphim, can you upload that pic again. Maybe to another service in a bigger quality?

I have tried to upload the images files directly, but I go into "manage attachments", "Upload File from Your Computer", point it to the BLIGHT.JPG, but I always get "upload of the file failed". I am within the size limits, anyone have any ideas what else causes image uploads to fail?

http://www3.bc.sympatico.ca/joeser/blight.jpg
Figured it out at last, just attach image with the icon, not manage attachments.