Sharp GX20 Service Manual - Page 59

9. Back light does not turn on. CONFIDENTIAL GX20 Do the keypad tones and ring tone sound from the speaker? YES Voltage of VBAT_AP applied to FS401? NO Jumper (TPB333 to CN305 36, 37 pin) or Relay FPC_A, CN305, CN201 defective. NO Jumper (CN201 2 pin to FS401) defective or defective mount- ing. YES Defective mounting or blowout of FS401. Voltage of VBAT_AP applied to IC404 6 pin? YES Which display does not light up? Main or external? NO NO Apparance, mounting and continuity properly given to FS401 (Fuse)? YES C465 and C466 defective. Only external display back light. H (To page 2-54) Only main display back light or both displays' back lights. Is the main display back light set to ON? YES NO ON Setting by the following menu. Settings → Phone settings → Main display → Back light NO Does the back light turn on? YES Nondefective. When the external display back light does not light up. H (To page 2-54) Are appearance and mounting of CN402 properly given? NO CN402 defective. YES Dirt and foreign matter detected at the back light FPC terminal? Back light FPC properly inserted in CN402? YES Voltage of 13 to 24 V applied between TP428 to TP429? Back light FPC defective or CN402 defective. NO NO Clean the back light FPC and insert it again. Then does it light up? YES Nondefective. YES Back light FPC defective. NO Does the back light slightly light up as the auxiliary light? YES Voltage of 3 V applied to Q404 gate (G) terminal? YES Voltage of less than 10 mV applied to Q404 drain (D) (R453 side) terminal? YES R453, R437 and IC404 defective. IC104 or Jumper (IC104 42 pin to IC404 4 pin) defective and defective mounting. NO NO Is the pulse shape sent to IC404 4 pin? (Don't hold to Low?) YES IC404, L410, L411 and D413 defective. NO IC104 defective. NO Q404 defective. (0.95 mV at drain terminal) 2 - 53