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Home Kenwood TH-D74 / TH-D75 Extended Transmit Mod

Moleculo

Ham Radio Nerd
Apr 14, 2002
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Updated 4/29/2024 for TH-D75 Mod:
I now own the new TH-D75. The modification is the same, but the component is now labeled "R2". Everything else is the same.

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I've owned the Kenwood TH-D74 since the first week it became available and finally decided to perform the extended transmit mod. Some of the sites that have already published this mod make it seem like a big deal, but it's really pretty easy. Here are the steps:

1. Remove the antenna and rotary knobs on the top right. The rotary knobs just pull off.
2. Remove the SMA nut. If you plan on doing this type of work for all types of HTs, you should consider purchasing the proper tool for the job. I use one of these inexpensive $7 wrenches that you can find on ebay: https://www.ebay.com/itm/3108085729...pid=5336136228&customid=&toolid=10001&mkevt=1. After the knobs and SMA nut is removed, your radio will look like this:
5220-1508822916-880a9b835007c8805f35857d297402ac.jpg


3. Remove the battery and the four screws holding the aluminum back to the radio body.
5221-1508823065-d6e9de06242a545e26dcb2ca6f261b51.jpg


At this point, the front cover can be easily be removed from the body. You'll need to unhook the rubber PTT cover from the main chassis, which was already done in the pic above.

4. Once you separate the radio cover from chassis, lay the cover down on its face. There is a ribbon cable connecting the buttons to the main board; most of the instructions published want you to disconnect this ribbon cable but it is completely unnecessary.

5222-1508823116-93e5f19166fe1eccba6a7ee7993e28d7.jpg


5. On the main radio board, remove R761. I just used a fine point soldering iron and it came off easily.

5223-1508823623-0071e3d6b48a4feca066c0e8b0ecb0a8.jpg


Reassemble the radio, reset it and you're good to go. Here is the TX range after the mod:
136-174 Mhz
216-235 Mhz
410-470 Mhz.

I have not noticed any ill side effects from performing this mod.
 
Last edited:

Hi all! New to the forum. I did the mod and nearly everything works as it should, but I’m unable to scan at all. Any thoughts?

Daniel
 
First are you in memory mode. Key #1 puts you in VFO and Key #2 puts you in memory. Hold down the #2 key and it should start scanning your memories. While in memory mode if you hold down the right or left arrow on the joy stick you will scan through your memory groups you have assigned. I believe you should at least have GRP 0 and Weather to start out with.
 
Geez... it’s working now. I must have had some other setting turned on when it wasn’t working for me last weekend?? I was using the Nifty Mini-Manual and trying buttons 1 & 2 but it wasn’t working. Fussed with it for 20 minutes... Figured I broke it somehow with the mod. But now that I try it, it works like it should. Who knows...

Thanks for helping. Clearly I need to spend more time with the radio...
 
Your welcome. TH-D74a has as you know has many features which are easy to forget if you’re not using it on a regular basis. The Nifty Manual I find is very good. Enjoy it’s a great HT.
 
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Happy to report this method is essentially identical for the TH-D75A. On the 75, the resistor is labelled R2. Its in the same exact spot as on the 74.

Thanks to OP.

PXL_20240202_002921610.jpg
 
Hello,

I can't confirm that removing R2 for the TH-D75 extends the TX range. Removing R2 converts the radio in a japanese version. Have you really tried transmitting outside the bands?

Regards!
 
Hello,

I can't confirm that removing R2 for the TH-D75 extends the TX range. Removing R2 converts the radio in a japanese version. Have you really tried transmitting outside the bands?

Regards!
Yes,

I enjoy operating GMRS as its where I started my journey in radio. I've had quite a few conversations on my clubs local GMRS repeater since doing this modification.

Do you have one? if so did this method not work for you? Please share so we can learn more. I know there is a TH-D75E that does not include 1.25m, perhaps this would have a different effect on that version.

PXL_20240202_002937870.jpg
 
Yes,

I enjoy operating GMRS as its where I started my journey in radio. I've had quite a few conversations on my clubs local GMRS repeater since doing this modification.

Do you have one? if so did this method not work for you? Please share so we can learn more. I know there is a TH-D75E that does not include 1.25m, perhaps this would have a different effect on that version.
Hi,

thank you for your quick reply. Unfortunately in the european version neither removing R1 nor R2 (and both) doesn't allow you TX out of band. Removing R2 converts the radio in the japanese version.
I contacted Kenwood through our dealer and hope to get a response soon.

Best regards!
 
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Hi,

thank you for your quick reply. Unfortunately in the european version neither removing R1 nor R2 (and both) doesn't allow you TX out of band. Removing R2 converts the radio in the japanese version.
I contacted Kenwood through our dealer and hope to get a response soon.

Best regards!

I see,

In doing some research for the TH-D74E, it seems there is a 'reset' that must be performed.


I wonder if this is also required of the 75E. Seems worth trying.
 
Has anyone measured their output power before and after doing the MARS mod? I have done this to both my D74 and D72 and stangely enough I can't get more than about 2.5 - 3 watts out on 2m on both. However both measure almost 7 watts out on 70 cm! I am wondering if something happens that needs to be re-calibrated / adjusted in the programming mode after doing this.
 

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