Template:Repair Guide/Example

820-3662 NO NUMERIC KEYS/CAPS LOCK INVERTED/INPUT DELAY - TOUCHPAD ISSUES

The device arrived with the numeric keys on the internal keyboard non‐functional, despite a complete keyboard replacement. Visible moisture and sulfation were detected near the keyboard’s SPI controller (U4801).

🔍 Step-by-Step Diagnosis Visual inspection: Corrosion was found near the keyboard/trackpad controller area (U4801).

Voltage drop across R4814 (relevant resistor in the SPI circuit) was checked and confirmed expected values.

Chip replacement attempts: First attempt:

Replaced U4801 with a donor chip from board 820-3476 (MacBook A1502).

🟡 Result: Keyboard worked, but Caps Lock LED was reversed (lit when lowercase, off when uppercase).

Second attempt:

Used a chip from MacBook A1278 (Unibody).

🔴 Result: Severe input delay and overall poor keyboard behavior.

Final solution:

Replaced with U5701 from donor board 820-3332.

✅ Result: Keyboard fully functional, Caps Lock LED working properly, no delay, trackpad also fully operational.