Apw70 Lac391p Schematic Portable < HIGH-QUALITY | SECRETS >

I couldn’t find a specific schematic for the exact code "APW70 LAC391P Portable" — this appears to be a very specific or possibly mis-typed model number, likely from a portable speaker, power bank, LCD device, or small consumer electronics board.

However, here’s good schematic-related content to help you locate or reverse-engineer it: apw70 lac391p schematic portable

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3. Understand the schematic structure (typical for this platform)

Once you have the diagram, you will likely see these sections: I couldn’t find a specific schematic for the

• Power entry & filtering – AC/DC input, fuses, EMI filter.
• DC-DC converters – +5V, +12V, -12V for analog, +3.3V for logic. APW70 often contains a flyback or buck regulator.
• Backlight inverter – For CCFL or LED (LAC391P LCD).
• LCD interface – LVDS or parallel RGB signals, timing controller (TCON).
• Touch controller – 4-wire resistive (if LAC391P includes touch).

Common failure points & symptoms

• No output rails: bad input fuse / blown TVS / damaged input reverse-protection MOSFET.
• 3.3 V rail OK but core 1.2 V missing: damaged switching MOSFET or open feedback resistor for VOUT2.
• Intermittent boot / resets: weak POR cap, bad solder joint on EN/RESET, or overheating LAC391P.
• Excessive heat: shorted output caps, MOSFET failure, or incorrect inductor value.
• USB power not negotiated: damaged polyfuse, blown USB controller, or ESD diodes shorted.

Parts to keep in a repair kit

• Replacement LAC391P (if available), common MOSFETs, inductors (matching values), electrolytic and ceramic caps, Schottky diode or MOSFET pairs, polyfuse, TVS diodes, assortment of resistors (feedback sizes), flux, solder, and thermal paste.

The APW70 – Main Power Sequencer

The APW70 is a multi-channel power supply controller and sequencer. Its primary job is to manage the startup and shutdown order of different voltage rails in a portable system (e.g., +3.3V, +5V, +1.8V, Vcore). If the APW70 fails, the entire device will exhibit a “dead” state—no LEDs, no fan, no response. Power entry & filtering – AC/DC input, fuses, EMI filter

Key features of APW70:

• Input voltage range: 4.5V to 25V (ideal for battery or AC adapter input)
• Up to 3 integrated synchronous buck converters
• I²C interface for voltage programming
• Built-in soft-start sequencing

C. Repair Databases (Paid)

• ElektroTanya – Free, but requires an account. Search “APW70 LAC391P service manual.”
• Repair.wiki – Community-driven, includes boardview files (.fz, .brd) for portable devices using this chipset.

D. Reverse-Engineering from a Physical Board

If you have a non-working board, use a multimeter in continuity mode:

• Identify the APW70 and LAC391P (look for 48-pin and 16-pin packages near large inductors).
• Draw the connections from VIN → inductor → output caps → load.
• Compare to the generic buck converter topology to reconstruct the schematic.

Step 2: Check the LAC391P Standby Rail

• The LAC391P should generate a 5V_ALWAYS rail (or 3.3V_ALWAYS). Measure at its output inductor.
• If 0V, check pin 11 (VIN) for 19V, pin 3 (EN) for >1.5V. If EN is low, trace back to the power-on button or battery management IC.

2. Where to Find the Real Schematic

• ElektroTanya (elektrotanya.com) – Search LAC391P or APW70.
• Badcaps.net forums – Post clear board photos; members often share repair schematics.
• AliExpress / Taobao listings – Sometimes sellers include PCB photos or block diagrams for portable DVD/LCD boards.
• OEM repair sites – Try LAC391P schematic in quotes; might be from a Lacrosse or Lacetti portable device.

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