CAP/MARS TRANSMITTING MODIFICATION

FOR THE YAESU FT-7900R

by WC5WC

When I purchased my first FT-7900r, it was purchased for my wife's car.  At the time, I assumed the information to modify the transmit frequency range for authorized use outside the amateur radio bands would be readily available.  I was wrong.  Of the many searches I have made on the web for the specific information related to the FT-7900, I could only find information on the FT-7800, the predecessor to the FT-7900r.  I found a few references that mentioned the FT-7900 but they only said the mod listed for the FT-7800 should  work for the FT-7900.  That doesn't exactly leave one with a warm fuzzy feeling about a planned mod.  I also did not find any sites that showed an actual photos of the FT-7900 internal, what the board appeared to be like after modification, or clear photos of exactly where the mod should be made.  I did find some hand drawings showing the approximate location of the jumper and a partial of the IC. 

I finally decided to use the FT-7800 mod and take a chance that it would work.  Fortunately, it did.  The following is a documentation of my modification of my FT-7900.  I decided to post it so owners of an FT-7900 would have a mod file specifically for the FT-7900 and not have to spend several hours of looking and getting the same results I did.  If you need to have a wider range of transmit frequencies for Mars and CAP use, this mod will work.

Disclaimer

I do not claim that this mod will work for you.  It worked for me on the three FT-7000r's that I own.  If you are unsure of what you are doing, DO NOT ATTEMPT THIS MOD!  I used a BIG magnifying glass to see the circuit board and part clearly enough to make the mod.  You make the mod described at your own risk and I cannot be held responsible in any way for how this mod will work on your radio.

Important:  it is against the law to use this radio on any frequency other than those authorized by your class of license and license service.  This radio is NOT FCC type accepted for any radio service other than the Amateur Radio service.

Steps for making this mod.  I had to use a large magnifying glass the whole time I was working on this radio.  These parts are extremely small so be really careful!

1)  Make a backup of your programming before doing the mod.

You will loose all previous programming when you turn the radio on the first time after making the mod and you will need to reprogram your radio.

2)  DISCONNECT THE POWER CORD!

3)  With the radio facing toward you, remove the eight screws holding the top cover, lift the cover off and disconnect the speaker.

4)  With the radio still facing toward you, look in the front left hand corner (corner closest to your body), you will see the microprocessor.

5)  To the left of the processor, there will a row of eight (8)jumper solder lands on the main board

6)  With the radio still facing toward you, there will be two extremely small, black jumpers soldered across onto the main board.  The jumper that must be removed is the jumper closest to the front of the radio. The blue arrow points to the correct jumper.

8)  I used a 7.5 watt pencil iron from Radio Shack with the tip shaved to a very fine point and it was still about 4X larger than I needed. After I unsoldered the ground side of the jumper and then proceeded to accidently break the trace on the high side of the jumper, the thought occurred to me that it probably would have been easier to just cut the trace on the high side of the jumper!  That will be up to you and I have not specifically tried doing it that and leaving the jumper soldered to the board.

9)  Reassemble the radio, hookup power, and turn on the radio.  The display will momentarily totally light up as the radio performs an automatic CPU and memory reset.  When a frequency is displayed, hook the radio to a dummy load and check your transmit range.  Reprogram your radio accordingly.

You have now completed the extended transmit frequency range for the FT-7900.