Nokia 105 Rm - 908 Keypad Ways

Technical Service Report: Nokia 105 (RM-908) Keypad Ways & Troubleshooting

Device: Nokia 105 Model Code: RM-908 (Single SIM) Type: Feature Phone / Dumb Phone Issue Focus: Keypad Malfunction (Non-working keys, ghost touches, or complete keypad failure) Component Analyzed: Carbon contact keypad matrix and PCB (Printed Circuit Board) traces ("Ways")

Abstract

This paper describes the keypad matrix (keypad ways) for the Nokia 105 RM-908, methods to diagnose common keypad faults, step-by-step repair procedures, and recommended testing practices. It targets mobile repair technicians and electronics students. nokia 105 rm 908 keypad ways

Phase 1: Physical Inspection & Cleaning (First Line of Defense)

1. Disassembly: Open the handset and remove the PCB.
2. Visual Check: Inspect the Keypad Membrane (gold contacts). Look for carbon buildup or wear.
3. Cleaning: Use IPA (Isopropyl Alcohol) and a brush to clean the keypad contacts on the PCB and the membrane.
4. Carbon Pad Replacement: If the black carbon dots on the membrane are worn out, replace the keypad membrane. Alternatively, apply conductive silver paint to the PCB contacts to improve conductivity.

4. Common Failure Points in the "Ways"

Alternative Repair: Direct Jumpering from Keypad Contact Pad

If the motherboard trace is completely destroyed and the CPU pad is inaccessible, you can bypass the connector entirely: Technical Service Report: Nokia 105 (RM-908) Keypad Ways

1. Identify the dead key’s Row and Column from the matrix table.
2. Using a fiberglass pencil, expose the copper contact points on the keypad PCB (the carbon pads themselves – but be careful, carbon doesn’t solder well).
3. Instead, find the test points or via holes that connect to those Row/Column lines.
4. Solder a jumper between the Row trace and the Column trace of the faulty button? No – this will cause that key to remain pressed. Instead, jumper the broken line to a working point on the same Row or Column from another button.

Better approach: Replace the entire keypad flex if the flex itself is torn. The "ways" method is for motherboard-level faults only. Disassembly: Open the handset and remove the PCB

4. Repair Procedures

Step 5: Soldering the Jumper Wire

• Tin the exposed copper pads and the jumper wire tip.
• Apply a tiny amount of flux.
• Solder one end of the wire to the connector pin’s leg (or nearest healthy via).
• Route the wire carefully, avoiding CPU pins, RF shields, and mechanical parts (keypad dome sheet).
• Solder the other end to the CPU’s corresponding Keypad Row/Column pin or test point.

Important: Keep jumper wires as short as possible to prevent signal interference or ghost touches.

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.

Nokia 105 RM-908 Keypad Ways: Complete Guide to Tracing, Jumpering, and Repairing Keypad Malfunctions

Published by: Mobile Repair Hub
Difficulty Level: Intermediate (Soldering and basic schematic reading required)