The Acer Aspire 5336 and 5736Z series are built on the robust but aging Compal LA-6631P (PEW72) architecture. This platform typically features the Intel Mobile GL40 or HM55 Express chipset, paired with Celeron or Pentium Dual-Core processors. For a senior technician, this board represents the classic era of discrete buck converters and the transition into more integrated power management. While known for its durability, common age-related failures in the standby rails and the DC-IN protection circuit require a precise understanding of the Compal power-on sequence.
Board Architecture & Technical Specifications
| Feature | Specification |
|---|---|
| Motherboard Model / ODM Part Number | Compal LA-6631P (PEW72/82/92) |
| Target Laptop Series / Form Factor | Acer Aspire 5336, 5736Z, 5733 Series |
| Chipset / CPU Architecture | Intel Arrandale / Penryn + HM55/GL40 PCH |
| Super I/O (EC/KBC) Controller | ENE KB926QF D3 |
| Key Voltage Rails & Switching Coils | +3VALW (PL27), +5VALW (PL28), +1.5V (PL24), +VCC_CORE (PL33, PL35) |
Real-World Motherboard Diagnostic Procedures
1) Input Power Stage & DC-IN Protection Circuit
On the LA-6631P, the 19V rail (+19VB) is managed by the ISL6251AHRZ (PU1) charging IC. If the laptop has no power and no LEDs, first check the voltage at PR3 (Current Sense Resistor). If 19V is missing here, inspect PQ1 and PQ2 (P-Channel MOSFETs). The ISL6251 must pull the gates of these MOSFETs low (approx 8V-9V) via the ACDRV signal. If the gate remains at 19V, the MOSFETs will not conduct. Verify ACIN (Pin 2) of PU1; it should be approximately 3.2V. If ACIN is missing, the charging IC will not enable the DC-IN path.
2) Standby & Secondary Rails Generation
The +3VALW and +5VALW rails are generated by the RT8206B (PU4). Before pressing the power button, PL27 must show 3.3V and PL28 must show 5V. If these are missing, check the LDO output at Pin 7 (LDO) which should be a steady 5V to power the EC. In this legacy platform, common failures include ceramic decoupling capacitors on the +5VALW rail shorting to ground. Ensure the resistance to ground on PL27 is >300 ohms and PL28 is >450 ohms. If resistance is low, inject 1V to locate the heating component, often a failing filter cap near the LVDS connector or the PCH.
3) Power-On Sequence & Signal State Tracking
When the power button is pressed, the KB926QF (U22) receives KBC_PWRBTN# and must release EC_ON (High) to enable the secondary buck converters. Following this, the EC sends PCH_RSMRST# to the Southbridge/PCH. If the laptop spins the fan for a second and dies, use an oscilloscope to check U18 (BIOS ROM) Pin 1 (CS#) for data activity. A corrupt BIOS or ME region on these HM55 boards often causes a "no-display" or "30-second shutdown" symptom. Always verify the 32.768kHz RTC Crystal (Y3); if the crystal is not oscillating, the PCH will never release PM_SLP_S3#, preventing the S0 state rails from activating.
Download Schematic & Boardview Files
Direct download link. Verified Compal LA-6631P schematic / boardview archive.
Professional Repair Assistance
Explore our technician resources:
- 🛠️ Diagnose No-Power & Short-Circuit faults step-by-step: Interactive Laptop Diagnostic Lab
- 🛒 Original Replacement Motherboards & IC Components: Official Spare Parts Mega Store
