Audio Brekthrough On Transmit on FT-450D by: Adrian, 5B4AIY You may be interested in how to resolve a problem with the Yaesu FT-450D. I was very happy with the FT-450D until suddenly when operating portable I was startled by a high level of distorted audio that was breaking through on transmit. The symptoms were: Even with the TX MONITOR set to OFF, highly distorted audio was audible on both the speaker and headphones when using SSB; The audio breakthrough was audible even when the AF GAIN was set to minimum; The level of the breakthrough was dependant upon both the TX power level and the antenna match. High power produced more breakthrough; and even on a dummy load the breakthrough could be heard although to a lesser degree than when using an antenna. The level also varied depending upon the VSWR. When using AM, the audio was undistorted. This all sounded like envelope detected RF breaking through into the audio amplifier. To cut a long story short, the transceiver had been modified for 5MHz operation when originally purchased. To do this the front panel is removed, and when you lift the front panel away from the die-case cast underneath is a screen held on with 6 self-tapping screws. These screw into the die-cast frame, and when they were replaced the technician took care not to over tighten the screws for fear of stripping the threads. Unfortunately, they did not tighten them enough, and over time the screen worked loose allowing RF into the compartment. The IC audio amplifier is located in this compartment, and an examination of the data sheet for the IC, LA4425A shows that it could easily rectify any RF appearing on its input terminals. The cure, simply tighten the screws securing the shield so that it makes full contact with the chassis - this may well require a certain amount of force. ....... ....... ....... Power increse for Yaesu FT-450 (from wwdx-forum) Cover for Transmit is Speaker, Side.(top). Remove Speaker cover, Install Watt Meter - With Antenna installed. Look for (6) Small Pots. TC 5400, VR5401, VR5402, VR5403, VR5404, VR5405. Adjust All to get the highst swing,Modulation. All pots are Black in color, Except the TC5400. It is on the other end of where you are working TC5400 is RED in color. ....... ....... ....... MARS Mod for FT-450 (from G6JVT's website) Important Notice This information is solely for use by licensed members of MARS (Military Affiliate Radio System) or CAP (Civil Air Patrol), and release to any other party is not authorized. Use of any Amateur Radio product outside of the Amateur band is at the users own risk, and no guarantee of compliance with specifications outside the Amateur bands is expressed or implied. The Limited Warranty does not cover damage caused by any attempt to modify an apparatus for out-of-Amateur-band operation, nor does the Limited Warranty cover damage to components that may result from out-of-Amateur-band use. New TX Freq range: 1.8-30 MHz. Modification Procedure: Units lot 07 and above the jumper JP4002 must be removed. Disconnect the power form the radio. Remove the front panel & the large RF shield to access the CONTROL PCB. Locate the solder jumper JP4002 as shown in the attached photos. Use professional de-solder tools and technique to remove the solder and open the contacts. Reassemble the radio and power cord. 1. Press and hold [ATT/IPO], [NB], and [AGC] keys, while turning the radio on. "SMADJO" will be displayed on the LCD as the memory address at the lower right side of the display. 2. Rotate the [DSP/SEL] knob CCW to show "TYPE" at the memory address on the display. 3. Briefly, press the [F] key, and confirm the "F" icon lights. While the "F" icon is displayed, press the [NB] key. "t" will be displayed at the right end of the frequency display. 4. Press and hold the [F] key for 3 seconds. A long beep will sound, the screen will clear and then the frequency will be displayed on the LCD. The procedure is complete. To return the radio to normal Ham Band mode, do procedure (1) and (2) as above, and then follow steps (3) and (4) below. 3. Briefly, press the [F] key, and confirm the "F" icon lights. While the "F" icon is displayed, turn the VFO knob to select "A" as displayed at the right end of the frequency display. 4. Press and hold the [F] key for 3 seconds. A long beep will sound, the screen will clear and then the frequency will be displayed on the LCD. Verify the radio will transmit in the Amateur bands only. The procedure is complete.