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MT6357 Boot Sequence

This video is a detailed, step-by-step mobile motherboard repair tutorial titled "Infinix Mobile Dead Fault Finding with Borneo Schematics", uploaded by the channel IC - Tech [00:00].

Key Highlights & Summary:
Device Problem: An Infinix Smart HD 2021 (X612) phone was brought into the shop in a completely dead state [00:11]. It drew zero current from a charger and went into full shorting (zero power supply readings with a beep) when pressing the power button [00:43], [02:57].
Diagnosis via Cold Testing & Schematics:
Using a multimeter and Borneo Schematics, cold testing revealed shorting on a buck coil (L405) associated with the VS1 output line [05:07], [07:17].
Visual inspection showed that a critical 1-ohm resistor (R401) on the VPH supply was missing and bridged improperly by a previous technician, causing internal IC damage [12:02], [12:30].
Power IC Replacement:
The technician desoldered the damaged MediaTek power IC (MT6357MRV) using a hot air gun, cleaned the PCB pads, and installed a new MT6357MRV IC [14:00], [16:14].
After replacement, buck supply outputs and voltages were restored to normal [19:21], [21:18].
Solving the Stuck Booting / CPU Issue:
When tested on a DC supply, the phone showed low booting consumption (~0.03A) and stuck [22:45].
Further schematic tracing revealed that the external LDO component (U202) providing the crucial VA12 (1.2V analog supply) to the CPU's PLL clock/RAM controller had been removed by a previous technician [26:08], [26:40].
Bypassing the LDO:
The channel bypasses the missing LDO by running a jumper wire from an adjacent 1.2V capacitor near the eMMC to the VA12 output capacitor above the CPU [28:48], [30:10].
Result:
After installing the jumper and connecting the battery/charger, the phone successfully displayed the charging logo, took current, and booted up completely [30:46], [31:53].

Infinix Mobile Dead Fault Finding with Borneo Schematics by IC Tech Peshawar Step by Step fault finding of a dead mobile is shown in this video,...

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