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This is nokia 1800 test mode solution.When you press power button then displaying on your phone "Test mode". You can repair nokia 1800 test mode problem using this solution.
How to do this Work : If you face this problem then open your phone.Clean your phone goodly with petrol or thiner and hot with Stan light 5- 10 minute after that check your phone.If problem still then check yellow jumper and red mark resistor following above picture.