Flashing cable for Nokia DCT-3 phones

"Dejan flasher" cable

CAUTION: Trying to modify the built-in firmware of a mobile phone may render it practically unrepairable. This applies especially to phones that do not have a separate EEPROM chip for settings and calibrations (e.g. most Nokia 3xxx phones). Before trying to update the flash memory, you need to understand the functions of your flashing program and the whole flashing process, including any checksum updates required. NuukiaWorld does not give any support in flashing-related questions.

The most well-known unofficial flashing cable for Nokia DCT-3 phones is called "Dejan Flasher". Its original design has been made by Dejan Kaljevic in 2000. You may find the original design floating around the Internet in a file called flasher.zip. To help you in building your flasher cable, NuukiaWorld's design is described below.

Schematics

NuukiaWorld have not analyzed the actual operation of the Dejan's flashing cable. The basic idea is to keep the phone MBUS and FBUS pins in a specific state when powering up the phone, and then transfer the data between the PC and phone synchronously using MBUS pin for clock signal. This cannot be done using PC serial (COM) port, so we need to use the parallel (LPT) port, which allows generating the required waveforms.

Dejan's design seem to work, so there is nothing to modify. In my version of the schematics, the inverters in 74HC14 are rearranged for efficient layout on simple copper-striped board. Also the unused gates are tied to valid signals.

The diodes, capacitor and resistor generates power for the IC. The IC converts the 5-volt signals of the PC to close the 2.8-volt system of the phone, and that is why the IC is not powered directly from PC's 5-volt power supply. (And actually, PC does not provide its 5 V supply on the parallel port.)

Bill of materials

For this flashing cable design you will need the following materials:

Count	Component	Notes
1	74HC14 (DIL case)	there is no space for an IC socket
2	1N4148
1	4,7 kΩ
1	100 Ω	required only if Vpp is used
1	100 nF	multi-layer ceramic capacitor is small enough
1	D25 male connector
1	D25 connector case	plastic with enough free space
	copper-striped board	see the layout picture below
	cable (4...6 wires)	for connection to the phone connector
1	phone connector	not sold on regular stores, you need to improvise

Layout

Because the circuit is rather simple, I did not make a real PCB for it. Instead of it, I used simple copper-striped veroboard. It is possible to fit the circuit directly in D25 connector case so no separate box is required.

The board is pushed between the D25 connector soldering pins so that pins 1...13 (numbered on the connector) are on the copper-striped side of the board. Because connector pin-spacing does not match the 2.54 mm raster of the board, you need to position the connector so that each of pins 1...6 and 11...13 touch one copper stripe without possibility of short circuits. You need to remove the copper at pins 7...10 (black area in the layout picture) to avoid short-circuits.

Note that the layout picture on the right is viewed from the component side. So the pins 1...13 of the D25 connector shown in the picture are actually on the opposite side of the board and pins 14...25 (omitted from the picture) are visible on the component side (the copper-free side).

The diodes must be soldered so that they do not make any short-circuits. I have wired them onto the component side directly through the first available holes (see photos). The copper must be naturally removed around those holes. Only one pin is used on the other row of the connector; pin 22 is connected with a wire to the circuit (see picture).

Finally you need to find a connector for your phone, and use a suitable cable to connect the required signals from the board to connector. You will need to connect at least signals MBUS, FBUS Tx, FBUS Rx, and GND. For Nokia 3210 you need to connect also Vpp (as far as I know). On 3210, connection to Btemp is optional but if it is connected you probably do not need to press the power button manually to start the flashing operation. — If you do not need Vpp or Btemp signals, you may leave the 100 Ω resistor and corresponding wires unassembled.

For pin-outs of some DCT-3 phones, visit NuukiaWorld's old FBUS/MBUS cable pages.

3.1.2006 nuukiaworld@gmail.com
No email support or answers to technical questions.

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