We have a full turn-key production line to our products in China. One of the main components in the product is CC-430 microcontroller. Our product is using in US and EU markets and CC-430 configured accordingly. For EU market we are using band 433MHz with Channel=5 (Tx frequency is 434MHz), for US market we are using band 915MHz with Channel=0 (Tx frequency is 915MHz).
In our last production batch, we got very low yield, about 70% in US products only. Almost all bad units are failed on RSSi (transmit) test. Our production partners sent us few failed units to analyze and figure out the problem.
We analyzed these units and found very strange behavior:
1) All units that were configured to band 915MHz with Channel=0 (Tx frequency is 915MHz), transmitted on different frequency, some units transmitted on ≈927MHz, some on ≈924MHz and some on ≈914MHz.
2) We re-programed these units to EU configuration, band 433MHz with Channel=5 (Tx frequency is 434MHz) and transmitted frequency was correct, 434MHz.
Its looks that some of the microcontrollers are partially damaged, that means low band is works ok and high band is damaged. I attached a picture of one of bad units with relevant marking data of CC-430.
Please note, this product exist more than 10 years and this is the first time that see a problem like this.
Please advise how we can check what happened with these components.