Talk-power mod for Icom m802
This document describes how to modify early Icom M802 radios for increased modulation with voice SSB transmission. Step 1 requires removal of three components in the control head and increases the mic gain, step 2 requires removal of a resistor in the main box and enables an internal speech compressor.
This modification should be done only by skilled technicians with experience with surface-mount (SMD) technology. These are tiny surface-mount components and the best way to remove them is with tweezers and a miniature temperature-controlled soldering iron. Extreme care must be used to not damage any other circuits or PCB traces. A good light and a magnifying glass is also required. If the proper equipment is not available, or if you are unsure of any of these instructions, do not proceed. These instructions are carefully written but may contain errors, they may not be clear, and radios can change. These modifications are made entirely at your own risk.
Step 1: Disconnect power. Open the control head (8 screws), do not disconnect ribbon cable to rear of case. Lay the control head face-down with knobs towards you, that is "bottom", side away from you is "top". Below the ribbon cable (located near top edge just left of center) is a metal shield (shallow box). Centered above the metal box, just left of a white plastic "clip", are two tiny resistors that are oriented vertically, and three that are oriented horizontally. The right-most of the two vertical resistors is R8229, our target: remove it.
Now go to the upper-right corner, and find the small round can (capacitor) closest to the screw in the extreme upper-right. Immediately left of that is a tiny black rectangle with 3 connections, that is Q8280 and our second target: remove it. And just below and to the right is another resistor, R8288 and our third target: remove that also.
Step two requires opening the main box (8 screws total). Orient the box with the printed circuit board (PCB) towards you (call this "down"), antenna connector away (call this "up"). Near the center towards the front is a metal about 2 inches x 4 inches, that is a "daughter PCB". Lift it off the main board, rocking it very gently and being careful of the metal grounding tabs. Under that daughter board is a black rectangular component with a million connections (the microprocessor), and above (towards the rear) and to the right of the microprocessor is a double row of 14 resistors per row, separated by a row of 14 small holes. Just to the right of the row of 14 holes is a single resistor. For reference, this lone resistor is just left and above the upper-left corner of the larger white connector that the daughter board was plugged into. Our target is R3403, which the right-most of the upper row of 14 resistors just described. Remove this. This allows the internal speech compressor to be enabled, see below.
Double-check, replace the daughter board, re-assemble and test. The increase in DC amps indicated by a "Link" battery monitor (or equiv) is the best guide to power output. Whistling next to the mic should generate 75-100 watts, about 8-14 amps increase.
To change the speech compressor setting, power off the radio, press and hold "F" and MODE keys, and power on. Rotate the left "group" (GRP) knob to select "COMP", and set it "on" or "off" with the right "CH" knob. (Make sure it is off for email use). When using the speech compressor monitor power output and avoid over-modulation.
--jec 6/2004