Icom IC-751 (IC 751 IC751) transceiver mods reviews software and diagrams

   
 
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26 February 2021, 5:23 UTC 


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Icom IC-751 (IC 751 IC751)
IC-751
Programming interface schematics for Icom:
Programming software for Icom IC-751 (IC 751 IC751) :
PDF User Manual for Icom IC-751 (IC 751 IC751) :
PDF Adjusments Procedures Manual with schematics for Icom IC-751 (IC 751 IC751) :
Schematics for Icom IC-751 (IC 751 IC751) :

Mods for Icom IC-751 (IC 751 IC751) :
    Icom IC-751 (IC 751 IC751) improvement for better CW full break-in
    Icom IC-751 (IC 751 IC751) Cooling, remote jacks
    Icom IC-751 (IC 751 IC751) Dual RAM back-up Battery Modification
    Icom IC-751 (IC 751 IC751) RAM Card Backup Battery Replacement Instructions
    Icom IC-751 (IC 751 IC751) Allow CW Xmit & USB recieve split mode
    Icom IC-751 (IC 751 IC751) to 37 MHz
    Icom IC-751 (IC 751 IC751) Bad Cap Problems
    Icom IC-751 (IC 751 IC751) General coverage mod
    Icom IC-751 (IC 751 IC751) Switch Matrix
    Icom IC-751 (IC 751 IC751) How to replace the lithium battery in your ICOM radio

Icom IC-751 (IC 751 IC751) technical specifications :  Icom IC-751 (IC 751 IC751) technical specifications



Icom IC-751 (IC 751 IC751) How to replace the lithium battery in your ICOM radio

Note: All this information is based upon the IC-751; if your radio is a different model the board references may be different.
  1. Go to Radio Shack or your favorite supplier and buy a lithium battery to replace the one in your radio. The actual type used is a BR2325 (3.0 volt 165 mAh), which Radio Shack does not carry. You can order this one from Digikey. I bought a CR2450 at Radio Shack (3.0 volt 500 mAh), which was the largest capacity unit they had in about the same size. I had to solder some short leads to this battery (quickly to avoid overheating), before I could attach it to the RAM board.

  2. Find a 5 volt power source to run the RAM board during the transplant. I used a modular plug-in unit rated at 4.5 volts @ 60 ma. I connected a 500 Mfd. capacitor to this supply and then added a resistive divider to reduce the voltage to 5 volts. You may need to re-adjust this divider to supply 5.0 volts after connecting it to the RAM board. Connect several feet of wire to the divider output, which will go to the RAM board.

  3. Remove the covers from your ICOM radio to expose the plug-in RAM board, which I found on the bottom of my radio.

  4. Turn the power on and locate the 5.0 volt and ground pins, which bring power to the board. In my ICOM radio service manual I found a board overlay for the 'RAM Unit', which shows the two connectors and labels the connections. While looking down at the board note two connectors on opposite sides of the board. Both connectors are closer to the same end of the board. The pin closest to the end of the board on the longest connector (J1) is pin 12, which is the 5 volt input. The pin closest to the end of the board on the shorter connector (J2) is pin 1, which is ground. If you connect a voltmeter between these two pins you should measure 5.0 volts. These are the pins you will connect your external power to.

  5. Turn off the power to your radio and remove the one samll screw that holds the RAM unit to the main board (you need a jewlers' screwdriver). Now you can remove the RAM board from the radio; remember from now on you do not want to touch any tools or other metal items to the board or it's components.

  6. With the board removed you now need to solder the two wires from your 5 volt power source to the board. You can solder to the small metal piece that is on the side of the connector toward the inside of the board; this will keep solder out of the connector pins. First make sure that your soldering iron does not have any direct ground connection to the board power source.

  7. After the external power source is connected, turn it on and measure the voltage being supplied to the board. You may need to adjust the values of the dividers to get between 4.5 and 5.5 volts. Disconect the power while making modifications.

  8. Now, with the 5 volts connected and on, you are ready to remove the old battery. Use an insulated tool to pry the battery off while heating the solder connections on the backside of the board. Only touch one of the battery connections at a time. Here you need to be careful not to touch any of the board traces or component leads.

  9. Once the old battery is removed, you can solder the new one in place, being sure that the polarity is correct. Now carefully inspect your job to be sure that the battery is connected to the correct pads on the board.

  10. Now you can disconnect the external power and unsolder the leads from the board.

  11. The final step is to re-install the board in your radio and continue to use it for many more years.

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