In a previous post available HERE I explained how to program RX CTCSS for the Motorola GM300 and M100. In this post I will describe the modification I made to short pin 3 and 4 to make the radio believe that the microphone is on hook in the the mic-clip for RX CTCSS to work.
If you want to use the radio for AllStar or Echolink then before you program the CTCSS functions you need to note that the radio has a remote hook switch on the microphone that is used when the radio is in monitor mode. The yellow monitor light on the front panel of the radio will be yellow and on under normal operation if programmed this way. Once you programmed the radio for CTCSS this light will still be on and CTCSS will not function as it should. The receiver will still open and allow any station in irrespective if CTCSS is programmed in the said radio. If you programmed the radio for CTCSS and hook the microphone to a mic-clip the monitor light will go off and the CTCSS will function. Unfortunately this will not work if you use the 8 pin microphone connector for AllStar or Echolink as the microphone will not be connected to the radio. You need to short pins 3 and 4 on the RJ-45. Pin 3 is the "hook" pin. Pin 4 is ground. By shorting pin 3 and 4 we make the radio believe that the microphone is on hook in the mic-clip for CTCSS to work. The other option only works with the extended logic board radios. You can program the accessory connector in wide mode function to use pin 7 and 14 (back of radio). Once programmed you can jump pin 7 (ground) and pin 14 (Remote Hook Switch Input) that will do the same as shorting 3 and 4 on the RJ45. In my case I cannot use the accessory connector as I do not have an extended logic board an therefor not the programming option in the RSS. The only option left is to short pin 3 and 4 on the RJ45. Please ensure that you use the correct pin outs. I will not be held responsible if you use the wrong pins. This will damage your radio!!!
Here is two images which is self explanatory:
The image above show the microphone and volume control board that must be unscrewed and disconnected from the logic board. To get to this board just unscrew the two hex bolts on the front panel of the radio. Once open remove the J8 (blue) connectors from the logic board. The head will now be loose form the body of the radio. Now unscrew the two hex screws, one holding the wires that go to the logic board and the other holding the mic and volume control board. Once done the board can be removed.
(Click on images for larger view.)
The image above show the microphone and volume control board removed from the radio header. Turn the board upside down as showed in the images. Now solder a bridge to the pins that are encircled in red. I used a insulated piece of wire to prevent any short circuiting. Once this is done you can assemble the radio and you hook switch modification is now complete. Once power is connected the yellow monitor light will be off and RX CTCSS will work. If you press the monitor button on the radio the yellow monitor light will lite up and CTCSS will be overide. Press the monitor button again and the light will go off and RX CTCSS is not active again.
