This information is to help clear the confusion about the ICOM IC-746 modification for out of amateur band transmissions. There are a couple of different mods floating around for the IC-746. For USA models, the following information is the ONLY mod for the IC-746! I verified this with my contacts at ICOM. They verified that this was the ONLY modification for the IC-746 (USA model) and that there were NO others. I then performed the modification and the radio transmits from about 100KHZ to 60MHZ and 118MHZ to 176MMZ so be careful with this mod!
Read the following instructions all the way through before performing this mod. Perform this modification ONLY if you feel capable of soldering VERY small surface mount diodes! Do this totally at your own risk.
Turn the radio upside down and position the front panel to your right. The main tuning knob will be to your lower right and the microphone connector to your upper right. This will orientate the radio in the proper direction to read the parts layout identification silk screening. (Note: the IC part numbers will be UPSIDE DOWN.)
Remove the twelve screws from the sides and bottom securing the bottom cover.
Locate the Circuit board with the Optional IF filters. The filters will be in the upper left hand corner of the circuit board. Look to the lower middle of the circuit board for silk screening that reads “Option UT-102”. (almost the center of the radio) Immediately to the right of the “Option UT-102” silk screening you will see two columns (14 positions in each column) of VERY small surface mount diodes in a tight configuration. I’ll call them diode positions 1-14. This column should have diodes in EVERY position 1-14. The next column to the right is diode positions 15-28. This column should have diodes in positions 15, 18, 20, 22, 23, 27 and 28 as shown below.
[01] [15]
[02] [ ]
[03] [ ]
[04] [18]
[05] [ ]
[06] [20]
[07] [ ]
[08] [22]
[09] [23]<-- Remove this diode only!!!
[10] [ ]
[11] [ ]
[12] [ ]
[13] [27]
[14] [28]
Diode 23 is VERY small and has a small “Y” on top of it. Use the finest pair of tweezers you have to remove diode 23 ONLY! Make sure you remove diode 23 only and NO other diodes! Make sure you have NO solder bridges as the diode pads are VERY small!
Use a clear piece of tape and tape the diode to one of the metal covered cans near the columns in the same orientation you removed it. This way you’ll have your diode to reinstall if you ever feel you need to and you’ll know the orientation of the diode.
This completes the TX modification. Replace the cover and screws.
TX should be from about 100KHZ to 60MHZ and 118MHZ to 176MMZ.
Do this totally at your own risk. Never, transmit out of the ham bands or your privileges.
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