Sharp GX20 Service Manual - Page 64

GX20 12. External display does not function. CONFIDENTIAL Does the main display function? YES Is the external display set to ON? YES Is external display to CN401 surely inserted? NO Refer to Troubleshooting, "Power does not turn on." (see page 2-42). NO ON Setting by the following menu: Settings → Phone settings → External display → External dis- play On/Off. NO Connector insertion defective. YES Clean the connector CN401 contact point and insert the external display again. Does it function? YES Voltage of 3 V ± 0.1 V applied to CN401 27pin? Proper appearance and mounting given to the jumper (CN401 27pin to VINT)? YES 3.0 V ± 0.1 V output at LCD_RST (CN401 8 pin)? NO Connector insertion part soiled. NO Jumper (CN401 27 pin to VINT Line) defective or defective mounting. NO IC104, C417, C473 and R413 defective or defective mounting. YES Proper appearance and mounting given to C426, C427 and C428? Electric potential on the both ends of C426, C427and C428 normal? Square waves output? C426: Square waves of approx. 3 V C427: Square waves of approx. 6 V C428: Square waves of approx. 9 V YES Voltage of approx 11.8 V output at CN401 29pin (TP419)? Voltage of V0 to V4 output? V0 (C418): Approx. 8.56 V V1 (C419): Approx. 7.33 V V2 (C420): Approx. 6.11 V V3 (C421): Approx. 2.42 V V4 (C423): Approx. 1.20 V YES External display unit defective. NO C426, C427, C428 and CN401 defective or external display unit defective. NO C418, C419, C420, C421, C423, CN401 and IC403 defective. Control signal line to IC403, or external display unit defective. * The backlight turns off. After a while, the voltage at TP419 becomes approx. 9 V. 2 - 58