2/23/97



Having owned an IC-751 for over 10 years, without replacing the lithium

battery that backs up the RAM, I decided that it was time to do something

about it.  I considered my options:



     1. Send the board back to Icom - $50-$75 plus weeks off the air.

     2. Buying the non-Icom EEPROM board - $120 dollars.

     3. Replacing the battery myself - $4.



I called AES and talked with one of their repair people, who convinced me

that I could do the repaair myself.  He said that to be sure that my

connections of the external power to the board, during the transplant, were

SOLDERED CONNECTIONS (no clip leads).  Following is what I did, successfully!

If you try this, I will not be responsible for any resulting problems.



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
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.



Good Luck,





73,



John, K9KA