Nokia 105 Rm — 908 Keypad Ways !!link!!

Nokia 105 RM-908 Keypad Ways: Complete Troubleshooting and Jumper Solutions

The Nokia 105 (RM-908) is a legendary feature phone, renowned for its extreme battery life and rugged build. However, even the "Indestructible Nokia" is prone to wear and tear, specifically on its keypad. After years of heavy texting and calling, the buttons often become unresponsive. For a mobile repair technician, knowing the Nokia 105 RM-908 keypad ways (track layouts and jumper solutions) is essential to bringing these devices back to life.

In this comprehensive guide, we will dissect the keypad IC layout, the row/column matrix, common faults, and step-by-step jumper ways to fix dead keys.

Step 3: Tracing the Ways (Jumper Diagrams)

Here are the most common Nokia 105 RM-908 keypad ways for jumper fixes. nokia 105 rm 908 keypad ways

Common Faults & Symptoms in Keypad Ways

Before opening the phone, verify these symptoms:

1. One entire row or column not working (e.g., Row 1: buttons 2,5,Up, Cancel fail).
2. Random buttons triggering – Caused by partial short between two ways due to corrosion.
3. No buttons work – Complete disconnection of common ground or all KBR/KBT lines.
4. Buttons work only after pressing hard – Dirty contact surface, but can also be a cracked via on the motherboard trace.
5. Liquid damage signs – Green/white corrosion eating the keypad way traces near the connector.

5. Locating keypad ways and common failure points

• Inspect PCB visually for:
  • Corrosion, rust, or liquid damage around keypad traces
  • Broken traces or cracked PCB near flex joints
  • Worn or flattened conductive pads on elastomer
• Check FFC connector and solder joints between keypad board and mainboard.
• Common break points: along fold lines, near screw posts, and where flex meets rigid PCB.

The RM-908 Keypad Matrix Mapping

The Nokia 105 RM-908 uses a standard 5x4 or 4x4 matrix. Below is the typical logic mapping for this model. Note: Always verify with a multimeter in continuity mode as board revisions vary. Nokia 105 RM-908 Keypad Ways: Complete Troubleshooting and

Rows (R1-R4) – Usually connect to IC pins via resistors. Columns (C1-C5) – Usually the input lines.

Typical Button to Matrix Mapping:

• Row 1 (R1): Up, Down, Left, Right, OK
• Row 2 (R2): 1, 2, 3, Calling Key (Green)
• Row 3 (R3): 4, 5, 6, * (Star)
• Row 4 (R4): 7, 8, 9, # (Hash)
• Row 5 (R5): 0, End/Power Key (Red)
• Column 1 (C1): 1, 4, 7, *
• Column 2 (C2): 2, 5, 8, 0
• Column 3 (C3): 3, 6, 9, #
• Column 4 (C4): Up, OK, Green, Red/Power
• Column 5 (C5): Left, Right, Down, (Usually unassigned or Flashlight)

6. Diagnosing keypad faults

Step-by-step:

1. With battery removed, visually inspect elastomer and PCB.
2. Re-seat keypad assembly and test with battery installed before further disassembly to confirm fault persists.
3. Use multimeter in continuity mode:
   • Identify row and column traces: probe across adjacent pad traces; press key to see bridging.
   • Measure resistance between trace and ground to detect short-circuits.
4. If intermittent, gently flex PCB and observe changes—this indicates cracked trace.
5. For multiple-key registration, look for shorted traces or conductive debris.

Phase 3: Component Replacement (Advanced)

If multiple keys fail or ghost typing occurs: The issue is likely the Keypad Filter/EMI Filter IC. One entire row or column not working (e

1. Location: Usually located near the bottom of the board or under a shield can close to the keypad connector.
2. Action: Apply flux and reheat the IC using a rework station. If heating fails, replace the IC entirely.
3. PDSA/CPU: In the RM-908, the PDSA (IC) controls the keypad logic. If the PDSA is damaged, all keys will fail. Reballing or replacing the PDSA may be required.

Scenario D: Power/End Key Dead

• Critical: Without this, you can't turn on the phone even if other keys work.
• The Way: The End/Power key is usually isolated or on R5 + C4. Look for a thick track running to the power management IC (PMIC) or a dedicated power-on resistor. Jumper directly from the switch contact to the nearest via that leads to the power IC.