During our repairs of Samsung mobile phones, we have come across several cases where the phone fails to establish a network connection, i.e. no signal reception. We have observed similar issues with the Samsung S8 SM-G950, Samsung S8+ SM-G955, and the Note 8 SM-N950 models. Even when a valid carrier's SIM card is inserted, the phone does not receive any signal as evident from the home screen.
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 installing the latest software, the phone still did not have a network. The phone was then carefully disassembled, and the antennas and antenna cables were found to be fully functional. The main board was then removed from the cell phone housing, and a visual inspection showed no signs of fluid, oxidation, or mechanical damage. Resistance measurements were taken 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 desoldered and the main board was prepared for mounting and soldering a new IC.
After measuring the resistance on the power line of IC U202, specifically on capacitor C417, we confirmed that the line resistance was over 2.5 KOhm, which indicated normal and correct conditions. This measurement confirmed that only the U202 IC circuit was faulty. We proceeded to position and solder the new Shannon 955 IC, restored and soldered the protective shield, and cleaned everything to prepare for reassembly.
Testing with a valid SIM card, the phone has a carrier signal and normally functions i.e. receive and send calls.The same IC circuit, Shannon 955, is also used in the Samsung S8+ and Note 8 models, so this malfunction may also occur in these phone models.
