Icom IC-756 (IC 756 IC756) transceiver mods reviews software and diagrams

   
 
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21 April 2021, 13:31 UTC 


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Icom IC-756 (IC 756 IC756)
IC-756
Programming interface schematics for Icom:
Programming software for Icom IC-756 (IC 756 IC756) :
PDF User Manual for Icom IC-756 (IC 756 IC756) :Icom IC-756 Instruction Manual
PDF Adjusments Procedures Manual with schematics for Icom IC-756 (IC 756 IC756) :
Schematics for Icom IC-756 (IC 756 IC756) :

Mods for Icom IC-756 (IC 756 IC756) :
    Icom IC-756 (IC 756 IC756) filter modification
    Icom IC-756 (IC 756 IC756) wide band modulation
    Icom IC-756 (IC 756 IC756) Spectrum Scope Adjustments
    Icom IC-756 (IC 756 IC756) ACC1 Audio Output Increase
    Icom IC-756 (IC 756 IC756) General Coverage H.F. TX Mod (1.6 - 30.0MHz)
    Icom IC-756 (IC 756 IC756) Expand TX Frequency

Icom IC-756 (IC 756 IC756) technical specifications :  Icom IC-756 (IC 756 IC756) technical specifications



Icom IC-756 (IC 756 IC756) ACC1 Audio Output Increase

Access to the Main Unit is required.

The "Line Level" audio output on pin 5 of Rear panel connector ACC1 is very low, with the manual stating 300mV. Normal Line Level is regarded as about 700mV. Although my MiniDisc Recorder had a gain control for its Analogue I/P it still couldn't make 0 VU. Here, by adding two resistors we can increase the gain of the audio appearing on pin 5 of ACC1.

  • Remove the bottom cover.

  • Remove 6 screws holding down Main Unit.

  • Remove screw on rear panel inbetween ALC & Send RCA sockets.

  • Remove heatsinking clip holding transistor to chassis.

  • Remove flat ribbon cable to J3 in far right corner.

  • Carefully pry PBA loose and fold over - see at left.
    (I actually had to remove RF Unit shield and loosen a shielded cable to allow the Main Unit PBA to fold out).

  • Locate IC-503, a NJM2058 OPAMP in an SMT SOIC14 package.

  • Remove W3 0603 SMT link.

  • Fit an 10k 0603 SMT resistor in W3's place.

  • Fit a 1/8w 5k6 through hole resistor from IC-503 pin 9 to ground.

We have effectively changed the OPAMP IC-503c from being a unity-gain follower into a non-inverting amplifier with a gain of approx 2.5.

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