As a first step, you may need to re-seat the connector cable of the SIM tray to the board.
If your are not sure which one it is, take the phone apart, examine every cable/connector on the board and/or just re-seat them all.
If you know which one it is, try also cleaning that connector with a cotton swab and 90%+ isopropyl alcohol (rubbing alcohol).
If the phone works with a different SIM (or as a precautionary step), clean the contact points of your original SIM card with an eraser or isopropyl alcohol. May be it collected something from your fingers during disassembly.
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I have this same problem, but now that I've attached the new digitizer assembly I don't think I can remove it. Did you find a solution?
crwdns2934271:0crwdnd2934271:0 Judy crwdne2934271:0
hi i have the same problem my samsung s4 mini wont read the sim card
i have clean the sim card the port too what else is there to do
please help me
crwdns2934271:0crwdnd2934271:0 james norton crwdne2934271:0