Nokia 100 contact service problem creates due to many reasons. Some time this problem creates when mobile lcd damage and points are short or lcd not compatible. Water damage phones also shows contact service. So to solve this problem first clean motherboard with electronics cleaner and also check phone jecks that there is no shortage. Apply normal heat after clean the circuit. Some time this problem solved by flashing mobile with latest software.
Check lcd points on motherboard with multimeter, if any point is short then brake this point and apply jumper. Below is full lcd ways diagram from original source.
Keep in mind almost 90 percent phones are recovered after clean circuit with cleaner and applying proper heat with heatgun
Nokia 100 Contack Service Jumper Problem Solution
Reviewed by Android Zone