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Date: 16 Oct 89 13:29:08 GMT
From: philmtl!philabs!!  (Robert
Subject: some IC37 mods

 Msg# TSP  Size #Rd Date/Time MsgID        From   To
 6051 BF   2985   0 1010/0541 1631_N2EYR   W2JIA  ALL@ALLBBS
 Sb: IC37 mods.

    Here is a list, transcribed from "220 Notes", of modifications for
    the ICOM model IC-37A. The 27A and 47A should be very similar:

     "We have been using [this mod sheet] in the Southwest Coast ever
     since the [IC-]'37 was in production. This one is the latest

      "The design problems of the '37 are greater than ICOM would lead
      you to believe. The [IC-]'38 has solved a great majority of the
      '37a problems.  However, the microphone and the UHF pigtail
      problems still remain.

       "The fix for the microphone on both rigs is the same. [see
       below] The fix for the UHF pigtail on the '38 involves removing
       the pigtail, and installing a bulkhead chassis mount BNC
       connector in the hole left by the pigtail assembly. Some
       elongation of the BNC connector holes is necessary for a good
       fit. A short coaxial jumper may then be installed from the board
       to the connector.

        "Now, here is the official Condor Connection IC-37 modification

        "1. To restore high-frequency receiver audio response, replace
        C-103 on the main unit with a .0022 uf mylar capacitor (that's
        2200 pf).

         "2. To restore LOW-frequency receiver audio response, replace
         C-106 with a .22 uf mylar capacitor.

          "3. To eliminate the distortion in the transmit audio,
          install a 4.7k ohm resistor inside the microphone case, in
          series with the white lead coming from microphone element.
          Once the resistor is installed, set the DTMF level pot to the
          middle of its range (this pot is the only one inside the
          microphone case). To complete the mod, set R88 inside the
          radio to the desired "mike" level.

           "4. To improve the receiver sensitivity, power output, SWR
           at the radio, and reliability, remove the RG-58 pigtail and
           the UHF connector extending from the rear of the radio.
           Install a BNC chassis mount, screw-in connector (UG-1094/U)
           in the hole left in the back of the radio. The new connector
           will screw in as if the modification was done at the

            "5. To greatly reduce chassis heating in the receive mode,
            remove the following components: R66, R67, R68, Q32, D42,
            and D44 in the main unit.  Install a 7808 [3-pin voltage
            regulator] on the transmitter power amp shield behind the
            space reserved for the optional voice synthesiser.  Thermal
            compound is recommended. Hook the input of the 7808 to the
            point where R67 and R68 used to connect. Hook the output of
            the 7808, in series with a 1N4001 diode, to J14-1. The
            cathode of the diode goes to the connector goes to  the
            connector, and the anode goes to the 7808.

                                          "---Mark Gilmore, WB6RHQ
                                          Newbury Park, CA."

                                           One note on the above - the
                                           BNC connector mentioned for
                                           the x7-series radios is sold
                                           by Radio Shack as 278-105,
                                           $1.39 each.

Note: I haven't tried these, proceed at your own risk.  WA2ISE
                                           0158z, 1390 msgs, #6500 last
                                           @KD6TH-4 MailBox>

Copied from the QRZ! Windows Ham Radio CDROM


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