Modifications for the Kenwood TH-78

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 (n2czf@wt3v.nj.usa) 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....
molson@bml4380.cpg.cdc.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 connection...

Open up the radio and you will see what I mean... Believe me, the fix is simple and it works.
C-17 design flaw


William_A._Kirsanoff@smtpgty.anatcp.rockwell.COM said:

"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

plus

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).

Brendan_Hoar@notes.pw.com suggests:

"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 D1 and 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 TH-78a mods.

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)

85.2x-179.995                   110.xxx-179.995

300.00-399.975

400.000-511.9875                400.000-511.9875

                                800.00-999.9875

* * * * * * * * * * * * * * * * * * * * * * * * * * * *

Receive                         Transmit

---------------                 ---------------

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 CALL channel.
Observations on post-mod performance


Rich Garcia (n2czf@wt3v.nj.usa) 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 better... Right?"

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.)"
Cloning


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 :-)

1. Set both radios to the same frequency.
2. Activate both radios by pressing the '0' key while turning the power on. The radios will display the word "clone".
3. 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 interference.)
4. Turn both radios off and then on again. The slave is now a mirror-image of the master radio.

Cellular Telephones


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 time).
Battery life on the TH-78A


wd6cmu@netcom.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.)
Game Mode


aviator@athena.mit.edu (who no longer exists), who credits
james@brokaw.lcs.mit.edu 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 again.

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 ):

  +---------------¾---

  |--  |          |     +-----------------------------+

  |--  | 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:

1. First you have to remove D2 for the standard EU bands (144-146 and 430-440 MHz).
2. Now control that the 2 green wires and the 5 other diodes are installed (D1, D3, D4, D5 and D6).
3. If you need band expantion and components location, please see the mods below.

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.

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.

1. Remove the shield at its four corners with a solder sucker and SMALL! iron.
2. 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.
3. Just as above you may remove the fifth diode to preform the extended receive and transmit modification.
4. 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!
5. 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.
6. For 300MHz go to the VHF band and repeat as above. Original bands are restored by repeating the "F Band" sequence.

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.

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 .....

CLONING:
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.)

1. Both radios must be on the same frequency.
2. Activate both radios by pressing the "0" key while turning the power on. The radios will display CLONE.
3. 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.
4. 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.

FREQUENCY EXPANSION

(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.