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
revision.
"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
sheet.
-
To restore high-frequency receiver audio response, replace
C-103 on the main unit with a .0022 uf mylar capacitor (that's
2200 pf).
-
To restore LOW-frequency receiver audio response, replace
C-106 with a .22 uf mylar capacitor.
-
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.
-
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
factory.
-
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.
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