This solution works on Nokia 5730 XpressMusic display problems like garbled, white screen, blue screen that is related to hardware failures. This solution may only apply if the flash firmware is already been done and seems to be okay and the flex cable assembly has been completely check or replace but the problem still exists.
In Nokia 5730 XpressMusic the LCD display data signal used two EMI-filter IC and a display data controller IC which is feeds from the application processor (CPU IC). see the repair guide picture layout.
One of the EMI filter marked with number two is also used for the keypad interface filtering designed. This IC shared the three input and output lines for the display data signal filtering.
You can check this tiny chips using the guide below before replacing them with a new one; the first one is approximately range 0 -100 ohms resistance value and the second one is up to 70 ohms per each input and output lines.
The last part which is heavily needs extra expertise to work with is the application processor if all of the above doesn't solve the problem.
By reworking or replacing the application processor is the last part that may solve the problem. You need to re-flash or re-build the firmware after you have replace it.