The Acer Aspire 4935 (and 4935G), built on the Compal LA-4491P (KAL90) motherboard, represents the pinnacle of the Intel Centrino 2 era. This platform utilizes the Intel PM45/GM45 Northbridge paired with the ICH9M Southbridge. For chip-level technicians, this board is a classic example of Compal's logic design from the late 2000s, featuring a robust power delivery system but also common failure points typical of its generation, such as the NEC/TOKIN capacitor degradation and ICH9M standby issues.
Board Architecture & Technical Specifications
| Specification | Details |
|---|---|
| Motherboard Model / ODM Part Number | Compal LA-4491P 0830 (KAL90) |
| Target Laptop Series | Acer Aspire 4935 / 4935G |
| Chipset / CPU Architecture | Intel Penryn (Socket P) + GM45/PM45 + ICH9M |
| Super I/O (EC/KBC) Controller | ENE KB926QF D2 |
| Key Voltage Rails & Coils | PL4 (+3VALW), PL5 (+5VALW), PL8 (+1.05VS), PL10 (+VCC_CORE) |
Real-World Motherboard Diagnostic Procedures
1. DC-IN Protection & B+ Rail Analysis
On the LA-4491P, the input voltage (19V) enters through the DC jack and must pass through the first and second protection MOSFETs (typically PQ1 and PQ2). These are controlled by the Charging IC PU1 (ISL6251). If you have no voltage on the PR1 current sense resistor (B+ rail), check the ACIN signal on Pin 2 of PU1. If ACIN is below 2V, the IC will not pull the gates of PQ1/PQ2 low (for P-Channel MOSFETs) or high (for N-Channel), preventing power from entering the system. Common failure: Leakage in the ceramic decoupling capacitors on the B+ rail leading to a 0-ohm short to ground.
2. Standby Rail Generation & RTC Reset
The Always-On rails (+3VALW and +5VALW) are generated by PU4 (TPS51125). Before pressing the power button, verify that VREG3 (3.3V LDO) and VREG5 (5.0V LDO) are present on PU4. If these are missing, the Super I/O KB926QF will not be powered, and the board will be completely dead. A unique issue with this generation is the 32.768kHz crystal (Y1) near the Southbridge. If the Southbridge (ICH9M) does not receive a stable clock or if the RTCRST# signal is low due to a depleted CMOS battery or shorted diode, the board may fail to trigger the power-on sequence.
3. Power-On Sequence & The NEC/TOKIN Factor
Tracing the sequence: Once the power button is pressed, the EC sends EC_ON to enable the 3V/5V switching rails. It then releases RSMRST# to the ICH9M. The ICH9M should respond by pulling PM_SLP_S4# and PM_SLP_S3# high. If the laptop powers on but immediately shuts down or freezes under load, inspect the NEC/TOKIN OE128 (or OE907) capacitor located on the bottom of the board directly under the CPU socket. These capacitors are notorious for high ESR (Equivalent Series Resistance) as they age. Replacing the single NEC/TOKIN with 4x 330uF Tantalum capacitors (low ESR) is a standard industry fix for stability issues on the LA-4491P.
Download Schematic & Boardview Files
Direct download link. Verified 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
