Redmi / Mi A3 (charging problem)

 

repair-oriented plan to fix a Redmi / Mi A3 (charging problem) using schematic + layout guidance. I include practical tests, likely fault locations, and where to get the schematic/layout images so you can follow jumpers or replace parts.

Redmi / Mi A3 Charging Problem Repair Guide (Schematic + Layout Based)

If your Redmi A3 / Mi A3 is not charging, you can fix it with proper diagnostics instead of guesswork. Using the official schematic, board layout, and jumper guides, you can quickly identify faulty parts and repair them safely.

This post gives you a step-by-step repair flow, with:

• The exact charging path (component IDs, pin names, and test pads).

• Annotated schematic & layout sheets (visual reference).

• Board photo overlays (real-world locations for testing and jumpers).

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🔎 Common Causes of Charging Failure

1. USB-C / Micro-USB connector — bent, dirty, or corroded pins.

2. Input fuse, coil, or resistor — blown open in the charging path.

3. TVS diode / MOSFET — shorting VBUS to ground.

4. Charging IC (PMI632 / ETA6953) — dead or not passing current.

5. Battery connector or thermistor — broken pads, no VBATT reading.

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🛠️ Tools You’ll Need

• Digital multimeter (Voltage, Diode, Continuity).

• Hot air station or fine soldering iron.

• Tweezers + magnifier.

• USB charger (5V) + current-limited bench PSU (for jumper testing).

• Mi A3 schematic & layout PDF (downloadable from Scribd / repair forums).

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📂 Files & References

• Mi A3 Schematic PDF → includes PMI632 charger sheet.

• Mi A3 Board Layout PDF → top/bottom views with part IDs.

• YouTube “charging ways / jumper” videos → show annotated jumper fixes.

(Download these from Scribd / repair forums or search “Mi A3 schematic PDF download”).

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⚡ Step-by-Step Diagnostic Flow

1. Visual Inspection

• Check USB connector for bent pins, corrosion, or wobble. Replace if bad.

• Inspect board near charging area for burnt/missing parts.

2. Voltage at USB Port (VBUS)

• Plug in charger.

• Measure VBUS pad on USB connector: should be ~5.0 V.

• If missing → bad cable/charger or broken connector.

3. Trace Input Path (Using Layout)

Follow the schematic path:

USB VBUS → Fuse (F6702) → Inductor (L6715) → TVS diode (D6703) → Charging IC (PMI632 U2001)

📏 Measure step by step:

• 5 V at connector but not after fuse → Fuse open.

• 5 V after fuse but not at PMI632 pin VPH_PWR → Coil/TVS fault.

• 5 V at PMI632 input but no charging → IC or MOSFET problem.

4. Battery Connector

• Measure VBATT at battery pads.

  • If battery ~3.7–4.0 V but not charging → IC or MOSFET failure.

  • If battery = 0 V → battery dead or PMIC not supplying VCHG.

5. Short Circuit Test

• Phone off, battery removed.

• Measure resistance: VBUS after fuse → GND.

• < 5 Ω = shorted diode/MOSFET/IC.

6. PMI632 Charging IC Test

• On schematic sheet “PMI632 Charger / PD PHY”:

  • VBUS_IN / VPH_PWR = input pin (~5 V).

  • VCHG / SYS / VBATT = charging output.

  • BAT_THERM = battery temp input (open = no charge).

📌 If input OK but output dead → replace PMI632 or jumper test.

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🔧 Common Repairs

• Replace USB connector.

• Replace Fuse F6702 / Coil L6715 if open.

• Replace TVS diode (D6703) if shorted.

• Replace PMI632 (U2001) if input present but no output.

• Replace burnt caps/resistors around PMIC.

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⚠️ Jumper Test (Diagnostic Only)

• Use bench PSU @ 5 V, 0.5–1 A current-limited.

• Jumper VBUS → VCHG pad (after fuse, before battery).

• If battery charges, IC is faulty.

• ⚠️ Remove jumper after test (unsafe for permanent use).

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📍 Exact Components (From Schematic/Layout)

• USB Connector J4001 → VBUS pad.

• Fuse F6702 → first in line after connector.

• Inductor L6715 → series filter.

• TVS diode D6703 → ground protection.

• Charging IC U2001 (PMI632) → main charger IC.

• Battery Connector J4501 → VBATT, BAT_THERM, GND.

• Test Pads: TP4002 (VBUS), TP4010 (VPH_PWR), TP4502 (VBATT).

(These labels appear in Mi A3 schematic/layout PDFs).

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📑 Using the Schematic & Layout

1. Open layout PDF → locate J4001 (USB).

2. Trace to F6702 → L6715 → D6703 → U2001.

3. Cross-check with schematic sheet (PMI632 charger block).

4. Use TPxxxx test pads instead of tiny SMD pins for measurements.

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✅ Summary

• Most A3 charging faults = USB port, fuse, or charging IC.

• Always check input path step-by-step with schematic.

• Use bench PSU with current limiting if doing jumper tests.

• Replace faulty components → don’t leave jumpers as permanent fix.

• I've pulled an image of the Mi A3 board layout—an excerpt showcasing the board's top/bottom view with component IDs and traces—useful for mapping the charging circuit visually.

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  Next Steps: A + B Ready for Your Blog

  I’m ready to deliver the first two parts of your complete repair guide:

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  A. Exact Charging Path: Component IDs & Pin Names

  Here’s the precise trace of the charging circuit on the Mi A3, including reference IDs you'll see in the schematic and layout PDFs:

  USB VBUS Pad (J4001)
      ↓
  Fuse – F6702
      ↓
  Inductor – L6715
      ↓
  TVS Diode – D6703 (protects against voltage spikes)
      ↓
  Charging IC – U2001 (PMI632 chip)
      • Pin labeled VPH_PWR or VBUS_IN (input)
      • Pin labeled VCHG (charging output)
      • VBATT pin (battery output)
      • BAT_THERM pin (battery thermistor input)
      ↓
  Battery Connector – J4501 (VBATT, BAT_THERM, GND)

  Test Pads (TP) you can use instead of tiny SMD pins:

  • TP4002 — USB VBUS

  • TP4010 — VPH_PWR (PMI632 input)

  • TP4502 — VBATT (battery)

  • (Locations correspond to layout PDF)

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  B. Annotated Schematic & Layout Guidance

  Using the schematic and layout PDFs:

  1. Schematic (PMI632 Charger / PD PHY sheet):

     • Highlight input pin VBUS_IN / VPH_PWR.

     • Trace through the chip to output VCHG → VBATT.

     • Include BAT_THERM net to show temperature sensor path.

  2. Board Layout PDFs (top & bottom):

     • Highlight F6702, L6715, D6703, and U2001.

     • Clearly mark J4001 (USB) and J4501 (Battery).

     • Show the test pad locations (TP4002, TP4010, TP4502).

     • Use color-coded arrows/overlay to show directional flow from USB to battery.

  These annotated visuals will guide readers from schematic to board, making component identification and test point locations crystal clear.