How to Build Your Own JTAG

By Mark Robinson

If you’re thinking about modifying or “unbricking” a cellular phone, network router or gaming console, you may be interested in creating a JTAG cable. JTAG programming cables provide a connection from your computer to the JTAG header found on many devices. Once connected via JTAG, users can flash custom hardware or reboot frozen or “bricked” devices. You can save the time and money spent searching for pre-built JTAG cables by making your own out of common electronic components.

Step 1

Add melted solder onto pins 2 through 5, pins 13 and 18 through 25 on the backside of the DB25 male connector.

Step 2

Cut one of the metal legs off each resistor. Leave enough of the legs behind for soldering the resistor to the DB25 male connector. Solder one of the cut leg pieces over pins 18 through 25 to create a bridge connection.

Step 3

Solder the short legs on the resistors onto pins 2 through 5 and pin 13 on the DB25 connector. Cut the long legs down on the other end of the resistors. Add melted solder to the remaining metal legs.

Step 4

Cut and strip wires 1, 3, 4, 6, 8 and 9 on the 10-pin flat cable. Cut the other wires down so they do not get in the way of the stripped wires or intrude into the connector housing. Place heat shrink tubing over the base of the wires. Add melted solder onto the bare wires.

Step 5

Solder the wires from the 10-pin flat cable onto the resistors and pins on the DB25 connector in the following order:

Wire 4 to pin 2 Wire 3 to pin 3 Wire 1 to pin 4 Wire 6 to pin 13 Wire 8 to pin 5

Step 6

Solder wire 9 to the bridge connection over pins 18 through 25. Slip the heat shrink tubing over the resistors and use a heat gun to shrink the tubing around them.

Step 7

Feed the other end of the 10-pin flat cable into the IDC connector. Line up wire 1 with the triangle on the connector. Squeeze the two halves of the connector together until the retainer loops snap over the ribs. The retainer loops should lay flat against the sides of the connector. Attach the strain relief piece onto the IDC connector.

Step 8

Attach the wire clamp onto the 10-pin flat cable near the DB25 connector. Tighten the screws on the clamp with a Phillips screwdriver. Make sure the wires are not pinched in between the wire clamp.

Place the DB25 connector and wire clamp into the bottom half of the DB connector housing. Place the top half of the housing over the bottom half. Insert the nuts into the screw holes, then tighten the screws with a Phillips screwdriver.