HM207 Mic Cable of IC2730A Dual Bander Reviewed Prior to Attempting Repair
HM207 Mic Cable of IC2730A Dual Bander is being visualized here, with two ends damaged and shield wire strands coming out. Next first step will be check continuity between two ends for each wire. That seems to be a bit difficult to do without cutting off the RJ45 connectors. I have checked continuity of the copper coloured shielded wire and that is fine between the two ends. Do wish me good luck so that I can complete a simple repair and get my radio back on air. Replacement cable is currently not available with the vendor from whom I bought this radio.
Here is the info which I found on online searches:
The Silver-Coloured Wires (Tinned Copper)
•Function: This is the dedicated Mic Ground (MIC GND) Shield.
•Purpose: It typically wraps directly around the sensitive microphone audio wire to protect your voice signal from AC hum, alternator whine, and RF interference.
•Connection: On Icom’s 8-pin RJ45 modular plug, this routes to Pin 5.
The Copper-Coloured Wires
•Function: This is the general System/Chassis Ground (GND) Shield.
•Purpose: It acts as the overall outer shield for the control lines (like PTT, Up/Down, etc.) to block general RF ingress from getting into the radio’s logic circuits.
•Connection: This routes to Pin 7.
Why are they separate?
•It is specifically designed to keep the Mic Ground and the Chassis Ground isolated from each other.
•If you twist the copper and silver wires together during a repair, you create a ground loop.
•In a mobile setup, this is the primary cause of that dreaded “alternator whine” on your transmitted audio.
Two other things inside that jacket:
•The stringy fluff: Those non-conducting threads are Kevlar or nylon aramid fibers. They provide mechanical strain relief so the actual copper wires don’t snap when you stretch the coiled cord.
•The Danger Wire: You You have seen the Red wire in the bundle. That is the +8V DC line (Pin 1). Never let this wire touch either of the bare ground wires. Shorting the +8V line to ground will instantly blow the voltage regulator ICs or microscopic SMD fuses inside the transceiver.