Chosen Solution
Everything working normally but when screen locked won’t wake up again. Problem appears after small work to u3500. The first problem observed, flash light not working Second problem observed, screen won’t wake up So replaced by series, u3300, u4000, u4020
What exactly did you do to U3500 and what was the original problem? Is the phone recognized by iTunes? When you replaced the Strobe, Chestnut and Backlight driver IC, did you probe the circuit to see if any of the voltage rails were missing or low? While there’s nothing wrong with a shotgun approach to troubleshooting, the challenge is when it doesn’t solve the problem. Then you end up with a whole bunch of variables (was the IC properly installed, bad IC etc.) and it makes it difficult to move forward. I would take a step back and see if the logic board will boot and is recognized by iTunes with nothing but the battery and dock connected. Then add one element at a time and address issues individually.
