Kenwood TH-D74A

Fully Assembled Kenwood TH-D74A

Teardown Video

6 minute video @ 3x playback speed showing full disassembly of the radio with commentary, full length video with no audio here.

Teardown PCB Pictures

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  Processor Board Top

• 

  Processor Shield Removed

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  Processor Board Bottom

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  Transceiver Board Top

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  Transceiver Board Top Zoom 1

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  Transceiver Board Top Zoom 2

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  Transceiver Board Bottom

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  Transceiver Board Bottom Zoom 1

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  Transceiver Board Bottom Zoom 2

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  FM Radio Module Top

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  FM Radio Module Bottom

Port and Test Point Identification

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  Test point locations for Boot[] pins which set the boot-up mode of the OMAP L138 processor, in this case to boot from NOR Flash.

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  OMAP L138 Boot Mode Selection, TH-D74 is set to boot into NOR Flash at the top of the list.

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  JTAG pinout

Modules and Interconnects

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  LCD Front

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  LCD Back

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  FM Antenna Front

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  FM Antenna Rear

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  Interconnect Top

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  Interconnect Bottom

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  Channel Selector

Mechanical Pictures

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  Front Case Interior

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  Metal Frame Front

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  Metal Frame Back

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  Metal Frame Connector Side

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  Metal Frame Button Side

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  Metal Frame Top

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  Rubber Gaskets

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  Screws and Knobs

Reverse Engineering Efforts

Kenwood TH-D74 connected to JTAGulator

High level goals

• Obtain a copy of the firmware for analysis/modification
• Understand how the radio works and what test ports are available internally

Obtaining firmware

• Determine routes of attack
  • JTAG Port
  • Serial Port
  • Hardware attack - Remove Flash Memory and read directly (possibly encrypted)

Initially the radio was opened and wires were soldered to some test points and an interesting PCB footprint that I suspected was JTAG as seen in the video below.

The serial port turned out to just be control data sent from the CPU board to the transceiver board, explained further below. Removing the flash memory is an option although it is a BGA package so not sure about soldering wires to it so it can be read out. Furthermore, the OMAP-L138 processor seems to have a few protection mechanisms. Encryption of the firmware is one of them so that route might be useless.

If a donor radio is stripped down to bare PCB then perhaps the boot-up config register values can be tweaked or other hard coded settings (usually using resistors) to alter the boot procedure and allow further debugging.

Understand how the radio works

There is a serial port labeled SCTX and SCRX (See Processor Board Bottom picture above), both of these lines appear to be transmit only from the top CPU board down to the bottom transceiver board. As the radio is tuned from one frequency to another the SCRX line has a lot of activity, when the transmitter is keyed up the SCTX line has activity. Below is a sample of what is seen on the SCRX line. Travis Goodspeed commented to me on Twitter that these commands seemed similar to the Rig Control commands sent from PC's to radio's to control them.

SCRX
J0000
K0000
G0283
`0
G1283
B06EE14
B0A03CE
B0C0028
B11E960
B180000
B140000
B1C2812
B200018
B280A68
G;7:3
K1900
a7:6
B1C2C12
B140000
B1C2812
B200018
B280A68
F41
J01
G;7:3
`0

Datasheets

Kenwood TH-D74A Datasheet - IC-701 - DRAM

Kenwood TH-D74A Datasheet - IC-702 - omap-l138

Kenwood TH-D74A Datasheet - IC-705 - FLASH MEMORY

Using the OMAP-L138 Bootloader

IC-707 - Not exact match but same family - WM8940