And you're doing that now, so that's good
Edit - Re: whether replacing the 'power IC' is going to fix your phone or not, that will depend on whether that's the only thing wrong with the phone or not. In many of these cases, it's the NAND that's corrupted (bad flash scrambles it), and that's all that's wrong. But if he says he's diagnosed your phone & discovered that's what's wrong/needs to be fixed, you don't really have any choice but to trust that he's right. Put it this way, if he's not & you do end up having to get a motherboard replacement, if I were in that situation there's no way I'd be paying for both the first repair and the eventual motherboard replacement when the issue could have been fixed in the first place by the latter.
But, we'll cross our fingers he's right & that fixes it for you