In this post, I will share my findings from a successful failure investigation of meter designed to transmit information.
I was tasked with investigating the source of the fault and identifying the root cause in order to characterize the type of failure – whether in the PCBA circuit, at the component level, in the antenna, or due to workmanship.
Background: A LoRaWAN 900MHz antenna is soldered to the mechanisms, functioning to receive and transmit data to the switchboard in the field.
The problem: UUT’s do not transmit or transmit very weakly, and do not pass a test.
The first step was to test the units in an RF anechoic chamber to determine whether any signal was being transmitted, even if it was extremely weak.
After testing several units provided by the contractor, I found that some had very weak transmission, some had no transmission at all, and others transmitted excellently.
I immediately suspected an issue with the antenna connection to the PCBA. To verify this, I removed the antennas from the units and conducted a wired transmission test using a spectrum analyzer.
The results confirmed that all tested PCBAs were functioning properly.
I examined the units under a microscope to assess the quality of the antenna soldering, and it It was immediately apparent that there were problems related to the antenna connection:
Excessive heating from the soldering iron caused damage to the antenna’s conductors.
Partial soldering of the connection VIA 
Failure verification:
After removing damaged antenna and installing a new one, I retested the units, and they performed perfectly.
Conclustion:
In this case, it was necessary to refine the procedures for the subcontractor to prevent such failures in the future.