When repairing Samsung mobile phones, we have encountered several cases where the phone does not have a network i.e. no signal reception. Similar failures occurred with the Samsung S8 SM-G950, Samsung S8 + SM-G955, and the Note 8 SM-N950. From the start screen, you can see that the phone is not receiving even though a valid carrier's SIM card is inserted.
When selecting manual network search in the settings menu, the phone searches for all bands but does not find a signal from any operator.
After the latest software is installed, the situation is identical-the phone still has no network.The phone was carefully disassembled and the antennas and antenna cables were found to be fully functional. The main board was removed from the cell phone housing and visual inspection showed that there were no traces of fluid,oxidation or mechanical damage.Measured the resistance on the elements of the board and by comparing the values with the correct PBA, a difference was detected on capacitor C417.
The measured resistance value on that line is about 45 Ohm. Since that line (1.8V) also supplies IC U202 Shannon 955-IC Circuit MF, we found this IC to be faulty. After removing the protective shield, the IC circuit was desolder and the main board was prepared for mounting and soldering a new IC.
By measuring the resistance to the power line IC U202, i.e. on the capacitor C417, the line resistance is over 2.5 KOhm which is normal and correct condition. In this measurement we confirmed that only the U202 IC circuit was faulty.We positioned and soldered the new IC Shannon 955, the protective shield was restored and soldered and everything was cleaned and ready to be assembled.
Testing with a valid SIM card, the phone has a carrier signal and normally functions i.e. receive and send calls. The same IC Shannon 955 circuit uses the Samsung S8+ as well as the Note 8, so this malfunction also applies to these phone models.