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| | {{Repair Guide |
| | |Device= |
| | |Affects parts= |
| | |Needs equipment= |
| | |Type= |
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| | == Problem description == |
| | <!-- |
| | Provide a concise description of the issue here. Be as specific as possible to help readers quickly determine whether or not this is the exact problem they are facing. |
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| '''820-3662 NO NUMERIC KEYS / CAPS LOCK INVERTED / INPUT DELAY - TOUCHPAD ISSUES'''
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| 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).
| | [[File:Placeholder image.jpg|thumb|Example image (Figure 1) -- No image yet. Help expand this page by uploading it!]] |
| | == Symptoms == |
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| | Detail all measurable or observable symptoms in this section. |
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| | * Symptom 1 (Figure 1) |
| | * Symptom 2 |
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| 🔍 '''Step-by-Step Diagnosis'''
| | == Solution == |
| | <!-- |
| | If the issue has a single, specific solution, provide it in this section and delete the sub-headers below. Otherwise, if there are multiple potential causes for the problem, outline the process of identifying the root cause and offer corresponding solutions below. |
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| Visual inspection: Corrosion was found near the keyboard/trackpad controller area (U4801).
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| Voltage drop across R4814 (relevant resistor in the SPI circuit) was checked and confirmed expected values.
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| '''''Chip replacement attempts:
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| '''
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| '''First attempt:'''
| | === Diagnostic Steps === |
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| Replaced U4801 with a donor chip from board 820-3476 (MacBook A1502).
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| 🟡 Result: Keyboard worked, but Caps Lock LED was reversed (lit when lowercase, off when uppercase).
| | === Repair Steps === |
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| '''Second attempt:'''
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| Used a chip from MacBook A1278 (Unibody).
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| 🔴 Result: Severe input delay, no trackpad and overall poor keyboard behavior.
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| '''Final solution:'''
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| Replaced with U5701 from donor board 820-3332.
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| ✅ Result: Keyboard fully functional, Caps Lock LED working properly, no delay, trackpad also fully operational.
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| '''⚙️ Technical Conclusion'''
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| The U4801/U5701 keyboard SPI controller contains firmware/configuration specific to each board model. These chips are not freely interchangeable between different MacBook series (A1278, A1502, A1398, etc.).
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| ⚠️ '''Using an incompatible IC can cause:'''
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| Reversed Caps Lock LED logic.
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| Noticeable input delay on keys input.
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| Malfunctions with the trackpad or power button.
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| ✅ '''Key Takeaway'''
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| “The keyboard IC (U4801/U5701) must come from a firmware-compatible logic board. Although they are electrically identical, their internal configuration depends on the board model and its interaction with the SMC.”
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| — Diógenes el Perro
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| 🛠️ Note: Neither the BIOS nor the SMC were reprogrammed during this repair.
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