The 5730 flex cable is combined with numeric and navigation keys, music player and volume keys, the power ON/OFF button switch, this includes the LCD screen display data signal connections, LCD LED back light voltage and the camera data signals and its power supply voltage. Earpiece audio signals.
If one of this data signals and voltage lines being cut off , due to a flex internal damaged may result the following failures and problems:
The display may result to white screen (WSOD- white screen of death), garbled, saturated display, a reversing display, blue screen, black screen or empty display due to lack of LED backlights.
Some of Numeric keypads button keys won't work, or keypad malfunction, music and volume key buttons malfunction.
Unable to power up, due to a cut of the power ON/OFF switch line paths.
The camera won't work or may result to camera hardware failure.
No earpiece audio sound recieve if the earpiece speaker line is cut.
Those failure above is just a common types of problems may results on a damaged flex cable on Nokia 5730 Xpressmusic. However, not all of those problems may consider and always suspects for a damaged flex because some of those problems might also occurs if its corresponding components that are connected to those particular circuits possibly might gets damaged also.
like for example, after replacing a new and working cable but the problem still exists, this problem may now lies on the corresponding circuit components to its particular connections.
View here for more repair hints and guides on keypads failure troubleshooting like the QWERTY keys that are also connected to the Numeric and Navigation keys on the flex ribbon cable of the Nokia 5730 XpressMusic.