Kenwood TH-D72 Extended TX mod

[Moleculo]

Here is how you modify the TH-D72 to transmit out of the 2m/440 band:

Take the radio apart by following this sequence of steps:

1. Remove the battery.
2. Remove the antenna and pull off the top dial knobs
3. Remove the two screws on the back.
4. Unlatch the rubber ports cover from the post on the back. Use a small screwdriver to slip under and it just pops off.
5. Pull the case up and off.
6. Detach the rubber button cover from the front and set it aside.

At the bottom front of the circuit board, below the number button pads, there is a small diode labeled D729. Remove that diode shown in this pic:

Remove the screw that holds the LCD display in place and gently lay it over. Underneath the display there is a row with three diodes labeled 1,2,3 near the speaker ribbon cable.

Remove diode D730 (labeled 1)

This is how the 3 diodes should be after mod:

1 - removed
2 - removed (USA version does not have it)
3 - must remain in it´s place (that means DO NOT remove it!)

Reassemble the radio and perform a FULL reset by going into the Auxilliary menu.

Transmit range is now:
136-173.995 MHZ
410-469.975 MHZ

note: Thanks to XE1BRX for updating the original version of this mod resulting in greater TX frequency range.

 

[Brlux]

any idea what the other diode is for?

 

[Moleculo]

any idea what the other diode is for?

Nope, I tested the radio with and without that other diode and didn't find any difference Without a schematic, it's impossible to tell what it does.

 

[Brlux]

So when removing the second diode you did not notice any change in TX range or new features like crosband repeat enabled? To bad, I wonder what it is supposed to do. Wasn't there a radio that had to be moded like this to allow crosband repeat? I think it was the European version of a radio.

 

[k5wh]

I tried this mod, and after resetting the radio from the Aux menu, as well as the F-Power on option, the radio cleared it's memories properly, but this did not seem to the enhance the UHF or VHF transmit range.
Any other tricks ?

 

[Moleculo]

Did you do the full reset, or VFO only? You need to do the FULL reset. Also, make sure your radio isn't in the auto repeater offset mode when trying to TX out of band. I thought the 440 expansion didn't work at first until I paid attention to the offset that was being activated, LOL.

 

[k5wh]

did the reset multiple times, and 449.995 is the highest area that it will transmit, in simplex mode..

 

[VA7RX]

I was just on the mods.dk site and the mod they show for the D72 is quite different. Admittedly it is for the E version, but their are 3 diods in a row on a different board. Any thoughts on this?

 

[Moleculo]

I saw that also. I did some (brief) playing around with that, but I couldn't find a combination that was useful, although I've already done the mod listed here which came from directly from Kenwood. Messing around with those one of the two diodes in the U.S. version did change things for me, but not for the better. In fact it limited the TX and RX range even greater. I decided to stop playing with it for now because the diodes are soooo small, it is very difficult to replace them even with a very fine point soldering tip.

 

[VA7RX]

Well, I just got an email from HRO that my D72 gets delivered tomorrow. I wonder how long I can keep my soldering iron out of it?

 

[k5wh]

I saw that also. I did some (brief) playing around with that, but I couldn't find a combination that was useful, although I've already done the mod listed here which came from directly from Kenwood. Messing around with those one of the two diodes in the U.S. version did change things for me, but not for the better. In fact it limited the TX and RX range even greater. I decided to stop playing with it for now because the diodes are soooo small, it is very difficult to replace them even with a very fine point soldering tip.

put the diode on just #2, removed from 1 and 3, and it becomes a Type=E radio.
you will lose the Weather band option though

 

[VA7RX]

So I opened my new TH-D72A today. It was home for 2 days before I opened it. I must be getting old.

I looked at the 3 diodes in question and see that the A version has #2 missing.

Has anyone played with removing 1 or 3 and if so can you tell us your result?

 

[XE1BRX]

OFFICIAL "BEYOND MARS Modification" FOR TH-D72A

This is the official Kenwood Mod for A (USA) model, I tested it and worked perfectly:

SAVE YOUR RADIO MEMORIES FIRST!

1. Remove diode D730 (labeled 1) (near the speaker ribbon cable)

This is how the 3 diodes should be after mod:

1 - removed
2 - removed (USA version does not have it)
3 - must remain in it´s place (that means DO NOT remove it!)

2. Remove diode D729 (On the lower part of the keypad board)

3. FULL RESET the RADIO
MENU>RADIO>AUXILIARY>RESET>FULL RESET

NEW TX RANGE:

136-173.995 MHZ
410-469.975 MHZ

PROCEED WITH CAUTION! I WILL NOT BE HELD RESPONSIBLE FOR ANY DAMAGE TO YOUR RADIO, IT´s UNDER YOUR OWN RISK!.

Remember that it is illegal to operate the radio outside the limits of your class license or permit.

 

[VA7RX]

Any brave souls try this yet?

 

[XE1BRX]

I try it, it worked perfectly, it´s from the original Kenwood document, and for the A model.

I am really happy that now the TX of my radio is expanded.

Please send me a private msg to send you the original PDF document.