I designed a board based on the EC200U-EU module, but I have a strange problem, the module turns on, but unfortunately it cannot recognize the SIM card and it constantly says that the SIM card is not inserted.
Of course, I should also mention that I connected the base of SIM_DET directly to GND, (of course, I also connected it to VCC_EXT for testing, which made no difference)
During the test, I noticed that the SIM_VDD pin has no voltage at all, is this normal? And how can I do other tests to solve this problem?
You can come out of the module flying wire, connect the SIM card holder test, if not normal test module SIM card interface related pin impedance (SIM_VDD, SIM_DATA, SIM_CLK, SIM_RST) is generally 0.3-0.6.