TPS900 can't detect the SIM cards like the above picture,please follow the below steps to check.
1.If the SIM card works on other device
2.If the SIM card inserted in the correct SIM card slot,because the PSAM card slots are beside the SIM card slots.
3.Check at "Settings->Network&Internet->SIM cards" if there have the SIM card numbers.If have,means the SIM card and slots are ok.
4.Check at "Settings->AboutPhone->Status"，If the “Baseband version” is blank or Unknow".If it is blank or unknow,means the system has issue or the Chip has issue.
Try to reburn the firmware and replace the mainboard.