SEMC posted some documents about problems with Z520.
Introduction
There is a problem with some Z520 phones where the phone has no network. When you look at the PCB, you may see that R1242 or R1245 are missing, damaged, or askew. (See attached word doc with photos)
Comments
The problem area on the PCB may appear as mechanical damage. You may even see scrape marks. This is not customer abuse. This damage is being caused in the factory. These phones should be repaired under warranty. Both of the parts (R1242 & R1245) are in the parts list and are shown on the component placing drawing. If you find the part missing, and if the damage does not affect other parts, and if the pads are still intact, replace the missing parts. If the part is slightly askew, and there is not solder damage, then leave it. (The example in the photo is acceptable as is.) If it is severely askew, (less than 50% contact coverage) de-solder and re-solder it.
http://www.savefile.com/files/2040182