Please can you inform the first time condition that you faced, then you decided to replace U0501 which use Qualcomm Pmi8940 / Pmi8937in this Redmi 4X water damaged
sample of answer : i change it, because this phone is dead boot, and i found by short on the vbat line, or short on vph_pwr or high current consumtion ( more than 200 mA after press power key ) or low consumtion after press power key or stuck on 100 mA more and less, please tell me your reason to change this PMI, since this PMI hase its ow job and responbility as power path control that generated VPH_PWR as main system power, that manages from two of sources VBAT or VBUS depend on its avaliablelity, beside its job to do charging controler
i just wanna make sure you do the correct thing for correct reason
its importand to know about each function of ic and their step before execute it, but now i just can assume you know what you do, and you do the neccessary things.
ok lets back to your question, since it entering Android boot / logo xiaomi, i believe power booting step is passed corerectly now, so i just assumes its current consumtion after press power key its good.
first step boot and since it still can be flash programming use ussual ways, i believe main processor ( AP ) and Primary bootloader ( PBL ) its has been load Secondary bootloader ( SBL ), and then Load the Android bootloader ( emmc apps boot ) to the RAM, if you confused about what i talking about, please take time to read about Booting procedure on android phone in Pragmafix Mentoring books
ok, now i just can assume you already understand about all basic thing about booting procedure, and you faced this kind of booting logo problem on redmi 4x
and since it CPU PBL working, SBL working, RAM working, Phone can be flashed but still remain the same ( which is there is possibility your emmc / emcp ic in WP condition ) MY QUESTION IS ? do you already try to chip off the emcp ic ( EMMC and RAM 221 package ) and try to read it, backup security thing insied just in case ypu need it after, and then check its health / report condition, or maybe prepare it to the best condition, including do the FFU to that ic if it supported ic models, or maybejust do repartioning if it not supported to do FFU ? or maybe factory reset to it ? and then re write thats EMCP use tested dump file ? or maybe you already prepare another EMCP ic that have simmiliar spesification to replace old EMCP, write all thing neccessary on it and put it on the board ? if you already do this, pleae report all things here.
if you arent do this before, and wanna do emmc execution in the last last last try, its ok you can try first to put WTR ( rf ic )as suspect, its ok since of this kind of models have problem on booting caused by this, for WTR problem so you can you can start to do partially erase the modem file, just to check "when modem firmware is erased so WTR will not able to works, so whenever your WTR is true in the bad condition, and it skipped by this erase action, your Redmi 4x will can boot to normal mode without any baseband working offcourse
that you know you now you maybe need to repair / replace the WTR ic and rewrite modem file partially
many possibilities, and all things will be easier if you understand the booting system and part jobs on this phone
i hope my answer can littlebit help,