Good question
LAN uses Sabre, TAM still uses Amadeus. Most likely, and regardless of your flight number, if you booked on lan.com/latam.com your PNR is a Sabre PNR (all six characters are letters). Try Tripcase and it should work
If you booked on tam.com, your PNR is an Amadeus PNR and Checkmytrip should work. Amadeus PNRs are alphanumeric
If you booked elsewhere, it'll depend on what your travel agent, issuing airline, etc, uses as GDS.