Modifications for the Kenwood TH-78
Also check on this site,
the site author asked me to remove the text on this page and just add a
link to his site instead, I decided to keep this page intact, and just
add the link to his information.
Basics of modifying the Kenwood TH-78a
To open the radio, follow the instructions on page 64 of the manual.
(Unscrew four screws and break apart the radio halves.) The two TX/RX busy
indicators (LEDs) have rubber seals placed over them. These have a
tendency to fall off when opening or closing the radio.
All position references in this document assume that you are looking at the
CPU board with the rotary encoders and TX/RX busy indicators at the top.
If you have installed the ME-1 EEPROM, I recommend that you temporarily
remove it to facilitate access to the diodes.
You'll see a brass shield about one centimeter square covering the
processor chip and the surface-mount diodes on the back half of the radio.
De-solder the shield's four corners and remove it. (I used an right angle
surgical tweezers in conjunction with the pin-point soldering iron to lift
the brass shield.)
Uncovered are the processor (which we ignore) and six surface-mount diodes,
numbered sequentially from one through six (D1 - D6), top to bottom. These
are about one millimeter wide; remember the note about skill and finesse.
New model radios also have two large loops of green wire, numbered one
through two (W1 - W2), bottom to top.
You'll need a pinpoint-tip soldering iron and some braid to wick away the
solder before you lift out the diode. Alternatively, Rich Garcia
(firstname.lastname@example.org) suggests leaving the diode in place. "I found if you
BRIEFLY touch the iron to the right side lead while gently pulling up on
the SMC diode it should completely come off without needing to apply heat
to the other side and further risk board damage."
After you perform some or all of the mods listed below, replace the brass
shield and re-assemble the radio. Then reset the processor (as documented)
and re-enter any frequencies into memory.
Potential case design flaw
In the course of performing mods on my Kenwood TH-78a dual band handheld,
I've discovered a potential flaw in the case design. While handling my walkie
one day (after the mods were done), the display went blank and I could not
turn the radio back on. With the radio split in half again, I could turn the
radio back on but discovered all the memories were erased. The cause turned
out to be some component pins on the front face coming in contact with the
square bodies of the two volume/channel/squelch switches, when the case is
screwed back together snuggly. I placed small strips of electrical tape on
the sides of the switches to insulate, and reassembled; problem solved. Now
I have to reprogram the darn thing....
email@example.com (Mark Olson) said:
There is a warning on some of the rig mod bulletin boards about this. The
problem is that pins on the back side of the PCB that is mounted on the
front half of the TH78 can come into contact with the volume control
housings mounted on the PCB on the other half of the unit. My radio had
this problem until I put electrical tape across these housings. Symptoms
were: Display blanking momentarily and the unit power cycling, sometimes
causing memory erase, when pressure was applied to the front of the unit or
to the volume controls. I originally thought that it was a loose battery
Open up the radio and you will see what I mean... Believe me, the fix
is simple and it works.
C-17 design flaw
"The 78A WILL lose C-17 on the control board if dropped, period. This
causes loss on receive audio on the left-hand side of the radio. The
solder pads for that cap are not big enough. If you find the need to
replace C-17, use a gap-fill cyanoacrylate glue like Zap-A-Gap (tm)
to increase the device footprint. I have learned the hard way.
Otherwise, I have found it to be a fine radio. My only problems have
been related to the C-17 issue and attempts to rectify it. Had I
been given the above advice, it would have been a one-time only
issue. As it is, I took out one of the microprocessors yesterday
looking for a bad solder joint that was induced by my attempt to
solve the C-17 problem (sigh). This radio gets a lot of use and
a lot of travel. C-17 is the only thing that I have broken with
the case closed.
Mutually exclusive mods
Some of these mods are reputed to be mutually exclusive. You must choose
one of the following levels of performance:
The "beyond MARS" mod - gets you the widest tx/rx
The "MARS/CAPS" mod - halfway there
The "extended receive" mod - more of a good thing
The "cross-band repeat" mod - a repeater that weighs almost nothing
There is no mods that manipulate diodes D1 or D2 (I've seen it suggested
elsewhere that this is toggles the USA/Europe-ness).
"I think removal of D1 causes "Forced Channelized Mode", at least on the
"new" radios. If you put both VHF and UHF memories into a TH78A without
power on, you are stuck in channel mode until you do a full memory reset.
Remember, you can't add frequencies or do any tuning in channel mode.
If you think about it, you'll want to be very careful not to let D1's circut
become an open circut.
The beyond MARS mod
This mod provides the widest possible range of tx/rx. The mother of all
To mod (early model): remove diode D5 only.
To mod (late model): remove diode D3 and cut wire W1. D5 has priority over
D3, so if you've already made the mods for the old model (which included
the removal of D5) you must resolder D3 into D5.
Yields RX 50-179.995, TX 136-179.995, RX 300-399.995, RX 400-511.995, TX
400-511.995, RX 800-999.995.
To use: buttons operate the same way as described in the "extended receive"
mod, except that you can transmit on a much wider range.
NOTE TO ALL: I haven't been able to verify the actual operation of my radio
on all these freqs. Kenwood talks about the difference between the
"dialable" range and the operating range. I'd like to come up with a chart
for each level of mod that combines the above and the two following
offerings. Help me, please.
* * * * * * * * * * * * * * * * * * * * * * * * * * * *
Left VFO Right VFO
50.000-85.2x (with beep) 50.000-110.xxx (with beep)
* * * * * * * * * * * * * * * * * * * * * * * * * * * *
50-135.995 (AM) VHF (NA)
136-179.995 " 136-179.995
300-399 (AM & FM) " (NA)
400-511.99 SUB-UHF 400-511.99
400-511.99 UHF 400-511.99
900-949.9875 " (NA)
50-179.995 (FM) SUB-VHF 136-179.995
The CAP/MARS mod
This doesn't cover as much room as the beyond MARS mod does, but may be
more appropriate for those who use the CAP or MARS frequencies.
To mod (both early and late models): remove D6 only.
Yields RX 118-173.995, TX 142-151.995, RX 400-511.995, TX 425-454.995.
The extended receive mod
This is the mod that's usually given to hams to pacify them (the beyond
MARS mod is closely guarded).
To mod (both early and late models): remove diode D5.
To use: press "F" for one second and then pressing the Band button will
switch the UHF VFO to a 800-999.995 MHz band and the VHF VFO to a
300-399.995 MHz band. The regular VHF VFO can now receive down to 50 Mhz.
The cross-band repeat mod
To mod: remove diode D4.
To use: press "F" for one second, then "0". Repeat to disable. The MHz
dot will flash when in repeater mode.
Toggle SHIFT button function
Press SHIFT during power-up This is described in the manual, but the
documentation is not complete. The TH-78A can operate in two modes: In
SPLIT mode, non-standard offsets (i.e. split frequencies) are supported,
but the default offset is not programmable. In SHIFT mode, non-standard
offsets are not allowed, but the default offset is programmable. To select
the default offset, press F for 1 second, then SHIFT. See p. 30 of the
manual for details on changing the default offset.
Toggle CALL button function
Press CALL during power-up. The CALL button can operate in one of two
modes. In the default mode (CALLSW), it switches between the call channel
and the last memory channel (if in memory recall mode) or last frequency
(if in VFO mode).
After toggling the CALL button functionality (VMC), it
will switch from the VFO to the last memory channel and then back to the
Observations on post-mod performance
Rich Garcia (firstname.lastname@example.org) observes "all original functions have
maintained the same which is great. Aircraft band which was accessible
before the mod remains with the same characteristics. It seems that
VHF-High band has improved a bit on sensivity where it was dead as a dog
before the mod (above 155.000MHz) but the 162.000 MHz band where weather
radio is is still a bit deaf for reception at any distance but about 20
Miles. This depends on your (or my) terrain and transmitter output power.
"On UHF all public safety frequencies up to about 500 MHz seem to come in
well but sensivity greatly drops from there (we really can't ask for more).
Frequencies can be programed in up to the 920MHz ham band but I have no way
of measuring sensivity. 800MHz works but the signals are very weak, you
must be near the transmitter for reception. Assuming you are in the town
or city where the transmissions originate it should work.
"Transmit is enabled up to and incl. 500MHz but after testing this on a
frequency counter I find that a signal is only generated to about 490 MHz,
even though the trans. LED shows output in the higher frequencies.
"Crossband repeat seems to work fine but the audio is unacceptable for use,
BE AWARE the radio gets HOT! Prolonged use or use on a busy frequency
would not be recommended. Also remember this is a dual band HT please use
a proper antenna while in this mode to avoid a high SWR, we should all know
Someone else said:
"I found that marine weather reports at 162.40MHz in my area were received
much better on the SUB-VHF band, than on the VHF band...
"If you are having problems with intermod, try switching bands (i.e. using the
SUB-VHF band rather than the VHF band.)"
The TH-78a's memory can be copied from one TH-78a to another TH-78a
entirely through radio waves "over the air" (i.e. without cables or other
special equipment). Theoretically, this could be done via repeaters,
although I've never heard it done. Allegedly this requires a mod that
includes removal of D5 or D6, but I haven't researched it.
Cloning is a real boon to groups that want a bunch of radios to contain the
same memories, such as amateur radio clubs, search and rescue units, and
people too lazy to program their radios. Of course, given that the ME-1
memory expansion unit has 250 memories, laziness is understandable :-)
Set both radios to the same frequency.
Activate both radios by pressing the '0' key while turning the power
on. The radios will display the word "clone".
Now, click the PTT button of the "master" radio. The radio will
transmit in the economy low power mode. This may take about 4 minutes for
fifty channels, or 20 minutes for the 250-memory ME-1. When the data has
been transferred, both radios will revert back to their original frequency.
(It is recommended that a dummy load be used to prevent unwanted
Turn both radios off and then on again. The slave is now a
mirror-image of the master radio.
Cellular phones operate at (tx) 824.040 - 848.970 (rx) 869.040 - 893.970,
within reach of your modified TH-78a. The increments are, however, every
30kHz; the TH-78a will only increment in 25kHz steps at this frequency
range, so the exact cellular frequency cannot be tuned in (most of the
Battery life on the TH-78A
email@example.com (Eric Williams) says:
Some people have complained about the battery life on the TH-78A. I came
up with these tips by checking out the power consumption under various
configurations. In the case of power-saver mode, figuring out the average
current with my DVM was impossible, so I ran the radio on a large capacitor
and timed how long it took to die. These tips won't solve everything, but
they might help.
The rig draws close to 2ma even with the power turned off, so don't leave
the rig off with the battery installed for several days and expect full
capacity to be maintained.
If you're only using one of the bands, shut down the other to extend your
battery's life -- current consumption with the squelch closed is cut by
almost a third.
If you're monitoring two frequencies on the same band, use the f2 button to
receive both simultaneously rather than scanning between them -- the
battery saver with two receivers will use about half the current of one
receiver that is scanning.
You can make up a battery pack by putting nickel metal hydride AA cells in
a BT-8 battery holder. A small strip of aluminum from the positive battery
terminal to the depression in the top of the case will allow you to
recharge the pack inside the rig. This will give you 1000mah capacity
without enlarging the size of the radio, and NiMH cells have no memory
effect. (But they *are* expensive.)
firstname.lastname@example.org (who no longer exists), who credits
email@example.com for "much of this".
To enter the game mode press M and PTT during power-up. Be careful not to
accidentally reset the memory, which happens with M + power-up. (Don't
freak; you'll see the same "all screen items lit" when entering game mode
as when you reset memory.) To exit the game mode at any time, press the
LAMP key. The volume, lamp, or frequency settings can't be changed while
in game mode.
The top part of the display will show "H.00", which represents the high
score. The lower part shows a scrolling message, "PRESS ANY KEY". Pushing
any key starts a "Follow Simon" type game. The display will briefly show
one of the characters '1', '2', '3', or 'F'. Press the corresponding key.
The game consists of repeating the displayed character sequence, which
increases by one character each round.
After you "win" the Simon memory game by getting correctly entering a
sequence of twenty characters, the next game is a draw poker game.
The way it works is that you choose your bet (from 1 to 10) by pressing '2'
to increment the bet and '5' to decrement the bet. Then, press 'F' to deal
the five cards. The face value of the cards is displayed, and the suits
can be seen at any time by holding down the PTT key. Any number of cards
may be discarded, and to select (or deselect) a card for discarding, press
the keys '1', '2', '3', '4', or '5'. If a card is selected for discard, it
is displayed "face-down".
Press 'F' again to draw new cards. Your new cards will be displayed, and
then if your hand is 2-pair or better, the screen will show the rank of
your hand on the left (2P for 2-pair, 4K for four-of-a-kind, etc.). On the
right the pay-off for that hand will be displayed. Your bet is multiplied
by the pay-off factor,and the resulting pile of cash is displayed in the
right hand side of the upper screen. (The left-hand side of the upper
screen contains your table stakes, which are initially 100 coins from
winning the Simon game.)
If you win the poker hand, pressing any key steps into the next stage. If
you lose the poker hand, your bet is deducted from your stakes and you are
asked to start another poker hand. In the next stage, you are asked
"TRYB/S" which means, "Do you want to try double-or-nothing in a guessing
game for Big or Small cards?" Press 'F' for yes, press TONE for no. If
you say no, your winnings are credited into your stakes and you are asked
to start another poker hand. If you say yes, then a single
shuffling/incrementing card is displayed on the left, and three stars are
displayed on the right. You have to choose to go for either BIG or SMALL,
by pressing '2' or '5'. You can keep pressing '2' and '5' to change your
mind. When you are ready, you must try to hit the 'F' key to stop the
rotating card display, and the card will show, and you will either win,
lose, or draw. If you draw, you have to play big/small again, I think. If
you lose, your winnings are gone and you can play poker again. If you win,
your winnings double and you are asked whether you want to play big/small
The payoffs on the poker are set against you, odds-wise; the
double-or-nothing game includes a draw, so the odds are against the player
there unless you can time hitting the 'F' key to win more than half the
rounds. I haven't managed to do this, so I don't know if there is anything
beyond this, all I know is that when the table stakes are exhausted, you go
back to playing Simon again.
TH-78 - antenna hints
Hello everybody! Recently I decided to check the performances of
small "Duckie" antenna specified as T90-0444-XX in TH78 manual.
I found that on 2 mtrs band this antenna, at first, has quite narrow
bandwidth and, at second, tuned about 144.000 MHz or even some lower
( at the same time 70cm bandwidth seems to be enough...).
Because of "integrated design" of this antenna it would be nonsence
to cut the top end, so I tried to find another way to tune it to the
middle of 2m band. At last, the problem has been successfully solved!
So, you can easy tune the central frequency up to 147 MHz - just place
a copper ring in the middle of conical surface of antenna ( between
"OO"s as shown below ):
|-- | | +-----------------------------+
|-- | K E N W O|O D | dual band antenna |)
|-- | | /+-----------------------------+
copper ring (about 13 mm internal diameter)
The ring made of 0.3 mm wire gave me frequency shift from 144 to 145 MHz;
if you need higher frequency, you should use wider ring ( about 4...5 mm
for 147 MHz ) - you can solder it of thin copper.
Don't use SWR meter for tuning! The best device is scanning scope or,
at least, simplest RF field meter and your HT as VHF generator.
TH-78A (U.S.A. version) --> TH78E (European version) MODS.
If you bought a TH78A in the USA you don't have the 1750 Hz repeater tone
access, but you can change that !
Apart from the well-known six diodes, the new CPU has 2 green wires.
In order to use the TH78A in EU, you must do the following:
Although the TH78A has a special bandpass filter for the US 70cm band, I could
not notice a decrease in sensitivity in the EU part of the 70 cm band.
- First you have to remove D2 for the standard EU bands (144-146 and 430-440 MHz).
- Now control that the 2 green wires and the 5 other diodes are installed (D1, D3, D4, D5 and D6).
- If you need band expantion and components location, please see the mods below.
There is a function change for 3 knobs; please see below and also p. 6 and 7 of
your INSTRUCTION MANUAL.
TH-78A --> TH-78E
LAMP --> TONE 1750 Hz
CALL --> LAMP
TONE --> CALL
Now, you can choice between the CTCSS tones and the 1750 Hz with the following
sequence: F + LAMP (the new TONE !) and then the right rotary encoder to make
your frequency choice.
Crossband repeat, extended RX/TX
Owner assumes all responsibility for modifying or using these modifications!.
The following mods will provide for Crossband Repeat and extended receive and transmit on the Kenwood TH-78A HT.
I believe other functions are also enabled by these mods. which I have not found yet but I will update the file as news progresses.
Diode #4- Crossband Repeat
Diode #5- Extended Receive and out of band Transmit.
Remove all screws and open radio as explained in the Kenwood manual for installing the memory expansion module.
On the back cover you will find the memory expansion module socket and a copper shield to the upper left corner of it.
Under this shield their will be a row of SMC diodes which are unmarked in a vertical configuration to the lower right portion covered by the shield.
MY observations... All original functions have maintained the same which is great. Aircraft band which was accessible before the mod remains with the same characteristics. It seems that VHF-High band has improved a bit on sensivity where it was dead as a dog before the mod (above 155.000MHz) but the 162.000 MHz band where weather radio is is still a bit deaf for reception at any distance but about 20 Miles. This depends on your (or my) terrain and transmitter output power.
- Remove the shield at its four corners with a solder sucker and SMALL! iron.
- Carefully count down from the 1st diode in the row to the fourth one and remove for crossband repeat.
HINT: I found if you BRIEFLY touch the iron to the right side lead while gently pulling up on the SMC diode it should completely come off without needing to apply heat to the other side and further risk board damage.
I used a pair of right angle surgical tweezers for this.
- Just as above you may remove the fifth diode to preform the extended receive and transmit modification.
- Reset the CPU (yes you will loose all of your programed memories! argh!) by pressing Function for more than one second and then "0".
YOU HAVE NOW COMPLETED THE MODIFICATIONS!
- For 800Mhz go to the UHF band with the band switch and press Function for more than one second quickly following with a press of the Band switch again. 8---.-- will appear.
- For 300MHz go to the VHF band and repeat as above. Original bands are restored by repeating the "F Band" sequence.
On UHF all public safety frequencies up to about 500 MHz seem to come in well but sensivity greatly drops from there (we really can't ask for more). Frequencies can be programed in up to the 920MHz ham band but I have no way of measuring sensivity. 800MHz works but the signals are very weak, you must be near the transmitter for reception. Assuming you are in the town or city where the transmissions originate it should work.
Transmit is enabled up to and incl. 500MHz but after testing this on a frequency counter I find that a signal is only generated to about 490 MHz, even though the trans. LED shows output in the higher frequencies.
Crossband repeat seems to work fine but the audio is unacceptable for use, BE AWARE the radio gets HOT! Prolonged use or use on a busy frequency would not be recommended. Also remember this is a dual band HT please use a proper antenna while in this mode to avoid a high SWR, we should all know better... Right?
After first booting up the CPU in the mod I found that the message screen showed "Cloning" so it seems that this radio now has cloning capabilities. After searching I have found that holding the "0" key and powering up the radio will display the clone feature, see below
for further explination.This leads me to believe that this HT may have some more "Hidden" features that I am trying to find, some may be useful.
Thanks to Gary KC8UD who sent me the following via packet .....
The TH-78 can be cloned without cloning cables or special equipment. It is done
entirely with RF, and, in fact, can be transmitted over the air, and even via
repeaters. This may be extremely useful for those users who do not have
the patience to program their own radios themselves. This application would
also be useful for clubs and user groups. (However, this can take as long as
50 minutes with the ME-1 expansion module. It is recommended that a dummy
load be used to prevent unwanted QRM.)
- Both radios must be on the same frequency.
- Activate both radios by pressing the "0" key while turning the power on. The radios will display CLONE.
- Now, click the PTT of the "master" radio. The radio will transmit in the conomy low power mode. This may take about 4 minutes for fifty channels.
hen the data has been transferred, both radios will revert back to the riginal frequency.
- Turn both radios off and then on again. They will now operate normaly while the slave radio has the same memory contents as the master radio.
(1) You can receive from 340 - 399.987 Mhz FM by removing chip diode D8 on the ontrol unit. To access this function, press the [F] key for one second, and then the [LOW] key. This toggles between AMATEUR, AIR band (AM) and 360 Mhz.
AM and FM modes are selected automatically, depending on frequency.
** Since "F" for a second and "Low" toggles the power output, I wonder **
There is also a couple of arcade type games on the TH-78A. To start the game you pres and hold [PTT] and [M] keys while turning the unit on. The first game is a follow me type game. The radio beeps and shows a sequence of numbers flashing on the screen. You have to match the same sequence on the tone pad. Each time the sequence gets longer by one number. You have to
keep remembering the sequence as one gets added each time. Once you get to a certain high score on that game, it breaks into a poker type game. To exit the game mode press the LAMP key at any time. The receiver still works in the game mode and you can adjust volume but no other features.
RG> The games seem to work fine and it is interesting that they have inserted that into the programing of the chips. Does anyone know of any further features in the radio be it games or radio functions.
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