If all rows/columns are open or shorted, suspect cracked BGA joints under CPU. Reball using 0.35mm stencil and leaded solder.
The Nokia 105 RM-908 does not use a traditional tactile switch matrix. Instead, it utilizes:
If multiple keys fail or ghost typing occurs: The issue is likely the Keypad Filter/EMI Filter IC.
CPU (MT6250)
+-----------+
| |
COL0 ---|P1.0 |
COL1 ---|P1.1 |
COL2 ---|P1.2 |
COL3 ---|P1.3 |
| |
ROW0 ---|P2.0 |---10k---VIO (2.8V)
ROW1 ---|P2.1 |---10k---VIO
ROW2 ---|P2.2 |---10k---VIO
ROW3 ---|P2.3 |---10k---VIO
+-----------+
Each column line to keypad pad: series 220Ω resistor (R200–R203).
Each row line to keypad pad: direct connection, but pull-up at CPU side. nokia 105 rm 908 keypad ways
This report outlines the diagnostic and repair procedures for keypad failures in the Nokia 105 RM-908. Keypad issues in this model typically stem from one of three causes: physical damage (liquid/carbon wear), keypad filter IC failure, or PDSA/CPU disconnection. The "Keypad Ways" refer to the trace routes connecting the keypad membrane to the main logic board.
The keypad is arranged in a standard Row/Column matrix. The "ways" refer to the copper traces running from the keypad contact points to the UEM (Energy Management/Interface IC) or microcontroller.
Typical Matrix for RM-908 (Estimated Pinout): If all rows/columns are open or shorted, suspect
| Key | Row Line | Column Line | Trace Label (Typical) | | :--- | :--- | :--- | :--- | | 1 | R0 | C0 | KBR0_KBC0 | | 2 | R0 | C1 | KBR0_KBC1 | | 3 | R0 | C2 | KBR0_KBC2 | | 4 | R1 | C0 | KBR1_KBC0 | | 5 | R1 | C1 | KBR1_KBC1 | | 6 | R1 | C2 | KBR1_KBC2 | | 7 | R2 | C0 | KBR2_KBC0 | | 8 | R2 | C1 | KBR2_KBC1 | | 9 | R2 | C2 | KBR2_KBC2 | | * (Star) | R3 | C0 | KBR3_KBC0 | | 0 | R3 | C1 | KBR3_KBC1 | | # (Hash) | R3 | C2 | KBR3_KBC2 |
Navigation Keys:
The Nokia 105 (RM-908) is a classic feature phone (2013 release) known for its durability, long battery life, and simplicity. Its keypad is not a standalone module but is integrated into the main PCB via carbon contact pads and a flexible membrane. The keypad ways refer to the conductive traces, test points, and column/row matrix lines that connect the keypad buttons to the baseband processor (typically a Mediatek or Spreadtrum chipset, often a MT6250 or similar). The Nokia 105 RM-908 does not use a
Understanding the keypad matrix is essential for diagnosing:
To avoid breaking the keypad ways in the future: