KENWOOD TH-79

1- Disconnect the battery and antenna. 
2- Remove tree screws from the back of the radio.
3- Remove one screw from the side under the speaker/mic/power jack cover.
4- Remove the CTCSS access cover.
5- Squeeze the bottom side panel where the battery inserts to release the
locking hooks.
6- Separate the two halves of the radio.
7- Locate and remove diodes D-304 and D-307 (Located on the back of the
front panel.
8- Reassemble the radio .
9- Reset the microprocessor (see owners manual).

NOTE: Jumper W301 is for MARS/CAP expansion only.

KENWOOD TH-79

ALL COUNTRIES MODIFICATIONS

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MODIFYING THE DESTINATION OF KENWOOD TH-79 DUAL-BAND HANDHELD TRANSCEIVER

A set of diodes is factory-configured to give the TH-79 its correct
properties for each export market. Since TH-79 is easy to bring, it is often
bought in a country else than where it is intended to be used most of the
time. The configuration you got at time of purchase may in other words need
to be changed to get adapted to your country. A typical example is if the
radio is bought in a so-called general version in the far east, when taken
into Europe it needs to be modified to allow 1750Hz tone call.

Before you open your unit for modification, you are advised to carefully
study below tables in order to plan your preferred configuration before you
start (you may also in some cases need to purchase additional diodes).

Also read the below warning and disclaimer before you continue:

1. It is technically possible to achieve wider frequency range than what
may be allowed in your country, doing so is of course against the law.
This may apply not only to the ability to transmit but also the
receiving range. Do not jeopardize the good reputation of Hams by
irresponsible action.

2. Modifying the configuration is a VERY delicate job, the diodes are in
size 0402 (= 1.0 x 0.5 mm) which requires both the proper tools and
practice how to handle such extremely small devices. You can forget
about doing this with an ordinary soldering iron at your kitchen
table. The operation calls for one or preferable two miniature
soldering irons plus the skills to fiddle with these tiny things
without destroying the board. If you are not completely sure you have
understood this document and the contents of its tables - refrain
from modifying your unit.

3. The manufacturer guarantee the performance only within the HAM bands.

4. This document does not claim to cover the subject 100%, it is merely
a collection of hints and experiences, and shall be considered as
such as there may be other aspects.

5. All modifications or attempts to modify, and any consequences thereof,
are ENTIRELY your own risk and responsibility. Also remember that your
product warranty will be void in the same moment you open the case of
your radio. Finally remember the possibility that this text-file may
have been tampered with during copying etc.

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TABLE 1: DESTINATION

Model Area Operate. Display Initial values TX-Rx unit no.
range range Freq/Step/Offset/Tone

TH79A-C China 136-180 144M/12.5k/+-5.7M/88.5
400-512 430M/25k/+-10M/88.5

TH79A-K America 144-148 144-148 144M/5k/+-0.6M/88.5 X57-4400-11
(118-174) (118-174)
438-450 438-450 440M/25k/+-5M/88.5

TH79A-K2 America 142-152 144M/5k/+-0.6M/88.5
rx-mod (118-174)
marse 420-450 440M/25k/+-5M/88.5

TH79A-K3 America 136-180 144M/5k/+-0.6M/88.5
TX-mod (67-180)
400-512 440M/25k/+-5M/88.5

TH79A-K4 America 142-152 144M/5k/+-0.6M/88.5
rx-mod (67-180)
mars 420-450 440M/25k/+-5M/88.5
+add. (400-512)

TH79A-K5 America 144-148 144M/5k/+-0.6M/88.5
rx-mod (67-180)
+add. 438-450 440M/25k/+-5M/88.5
(400-512)

TH79E-T England 144-146 144-146 144M/12.5k/+-0.6M/1750 X57-4402-71
430-440 430-440 430M/25k/+-1.6M -7.6M/1750

TH79A-X Austral. 144-148 144-148 144M/5k/+-0.6M/88.5 X57-4400-71
(118-174) (67-180)
430-440 430-440 430M/25k/+-5M/88.5

TH79A-P Canada 144-148 144-148 144M/5k/+-0.6M/88.5 X57-4400-11
(118-174) (118-174)
438-450 438-450 440M/25k/+-5M/88.5

TH79E-E Europe 144-146 144-146 144M/12.5k/+-0.6M/1750 X57-4402-71
430-440 430-440 430M/25k/+-1.6M -7.6M/1750

TH79E-E2 Italy 136-174 136-180 144M/12.5k/+-0.6M/1750 X57-4402-72
(118-174) (67-180)
410-470 400-512 430M/25k/+-1.6M -7.6M/1750

TH79E-E3 England 144-146 144-146 144M/12.5k/+-0.6M/1750 X57-4402-73
430-440 430-440 430M/25k/+-1.6M -7.6M/1750

TH79E-E4 144-146 144M/12.5k/+-0.6M/1750
432-438 432M/25k/+-1.6M/1750

TH79E-E9 144-146 144-146 144M/12.5k/+-0.6M/1750 X57-4402-73
430-440 430-440 430M/25k/+-1.6M -7.6M/1750

TH79A-M General 144-148 144-148 144M/12.5k/+-0.6M/88.5 X57-4400-21
430-440 430-440 430M/25k/+-5M/88.5

TH79A-M2 General 136-174 136-180 144M/12.5k/+-0.6M/88.5 X57-4400-22
(118-174) (67-180)
410-470 400-512 430M/25k/+-5M/88.5

TH79A-M3 General 136-174 136-180 144M/12.5k/+-0.6M/88.5 X57-4400-22
(118-174) (67-180)
410-470 400-512 430M/25k/+-5M/88.5

TH79A-M4 General 136-174 136-180 144M/12.5k/+-0.6M/88.5 X57-4400-22
(118-174) (67-180)
410-470 400-512 430M/25k/+-5M/88.5

Notes to table 1:
Intervals within parentheses show receive-only ranges.
The range 118 - 136 MHz is used in AM mode only.
Destinations C, K2, K3, K4, K5 and E4 are a bit uncertain regarding frequency
ranges, do not go for one of these unless you are prepared to experiment.

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TABLE 2: DIODE CONFIGURATION FOR EACH DESTINATION

D D D D D D D
3 3 3 3 3 3 3
0 0 0 0 0 0 0
2 3 4 5 6 7 8 Diode final figures for safety double-check:

C X X - X X - - 2356
K X X X X - X X 234578
K2 X X X X - X - 23457
K3 X X - X - - X 2358
K4 X X X X - - - 2345
K5 X X X X - X - 23457
T *
X X - X X X - - 2456
P *
E X - X X X X X 245678
E2 X - X X X X - 24567
E3 X - X X X X X 245678
E4 X - - X X X X 25678
E9 *
M X X - X X X X 235678
M2 X X - X X X - 23567
M3 *
M4 *

Notes to table 2:
Destinations marked above with an asterisk (*) do not have data, but are most
likely duplicate diode configurations with another destination (can have to
do with what accessories are supplied with delivery and so on).
The (X) indicates that the diode is mounted, (-) indicates empty position.

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GENERAL INFORMATION PRIOR TO MODIFICATION

1. The functions (as described by Kenwood) of the so-called destination
diodes are as follows:

"The following functions are made available by removing the
corresponding diode:
D302 Channel display mode
D303 (unknown)
D304 (unknown)
D305 Channel display mode and key lock
D306 Crossband repeater, answerback
D307 (unknown)
D308 Frequency extension
Clone and message paging reception is made possible by D308
frequency extension."

Personally I have not thought so much about the meaning of this
information since I found it quite puzzling when comparing different
destinations and their diode locations. My advice: forget this.

2. Extra goodies that you may have already in your station, or that may get
revealed by modification, are the extra bands that are almost
without documentation, here is how to test if you have them (not all
versions have) and how to reach them:

a) The air-band 118 - 136 MHz (AM only) can be achieved with any unit by
suitable modification (see tables above).

b) The 300 - 400 MHz band can be reached by in VHF/VFO-mode first
pressing the function key <F> and then the power selector <LOW>.

c) The 800 - 1000 MHz band can be reached by in UHF/VFO-mode first
pressing the function key <F> and then the power selector <LOW>.

3. As indicated in table 1, the frequency range that can be displayed by the
unit is not necessarily the same as the radio is technically capable of.
The easiest way to find out the range, is to set the lowest frequency
possible and then do a VFO-scan from that point. The unit will beep for
each step that is not supported until it reaches the real range. Also the
range 118 - 136 MHz is forced into AM mode shown by a wider decimal point
in the frequency readout.

4. Before you decide to modify you need to be aware of this; if you change
the configuration between TH-79A and TH-79E the case printing will not
be totally correct. On the TH-79A the button below the PTT actuates the
backlight of the display, and the rightmost button of the four round
buttons below the display actuates the CALL function, and the bottom left
button actuates tone. On the TH-79E the button below the PTT will become
the tone call button, while the right button below the display will
actuate the backlight. Therefore the text printed on the case will not be
valid for those two, personally I do not find it too irritating, but it
can perhaps be the day you like to sell it. Changing from A to E version
will also remove the CALL function (read more about it in your manual).

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STEP-BY-STEP DESCRIPTION

1. Shut off the radio and remove the accumulator. Take standard precautions
regarding electrostatic discharge hazards.

2. Remove the four screws that hold the case together, three of them are at
the rear, while the last one is hidden under the rubber-flap beside
the DC-inlet.

3. Fold apart the case halves. The volume knobs are fitted in the front and
the BNC connector in the rear.

4. Remove the plastic cover (holder/key top) covering the keyboard, the
purpose is to prevent damage since you get close to it when soldering.
Carefully examine the lock that makes it snap to the outer case half, no
great force is necessary once you understand how to disassemble it.

5. Locate the row of configuration diodes D302 - D308 at the bottom right
corner of board above the keyboard. Note the original positions of the
diodes just in case something would go wrong.

6. Make sure your soldering iron's) are clean and have the correct
temperature for this delicate circuit. Personally I would not
recommend using hot air soldering, there are plenty of components that
if accidentally heated may take damage, and the risk that components
around the diodes will start drifting around to a big (small) mess.

7. According to your choice from above tables, do your configuration by
moving and/or removing diodes to their proper places. If you would need
to add diodes, I would assume that any switch-type diode will do the job.
However, I have not tried it myself. Take care with the polarity of the
diodes. They are pointing down towards the edge of the board, all in the
same direction.

8. Now you should be ready to reassemble the unit, take a note of the new
diode positions and the type-number of the TX/rx-board to keep with the
schematic diagram of your station. Also, take the opportunity to get
impressed by the neat Kenwood assembly before closing the case again.
Do not tighten the screws more than necessary, they are fitted directly
into the plastic, which is also a reason for not opening too often.

9. You will note that when you turn on the power on your newly modified rig
it indicates that it has been reset. All your programming has been lost
when doing a modification (not really a problem, just as information).
Also, remember the button swap (see point 4 in general information).