Bad mic, or problem with rig?

Discussion in 'General Technical Questions and Answers' started by WB3CQA, Jul 27, 2021.

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  1. WB3CQA

    WB3CQA Ham Member QRZ Page

    I have an Icom IC-2410H, using the HM-56A hand mic. The rig and mic sat on a shelf for a few years, but performed normally when last used. Now when I try to use it, the rig is keyed up as soon as I turn it on with the mic connected. Without the mic, the rig seems to be acting normal. Should I suspect the mic or the rig?
  2. PA5COR

    PA5COR Ham Member QRZ Page

    You answered your own question, if mike is removed the transceiver acts normal so the microphone is at fault, check wiring in connector or inside mike.
  3. K7MEM

    K7MEM Ham Member QRZ Page

    I agree with PA5COR on the fact that it's probably the mic at fault. But it might be more than just a stuck PTT switch.

    The HM-56A mic uses a TMP47C452AF Micro Computer, with built in ROM and RAM, and runs off of the 8 Volts from the radio. The PTT in the mic is not just a simple switch. The PTT switch drives the micro, which then drives a transistor that goes to the radio. Make sure that the 8 volt power is getting to the mic and powers the micro correctly. The pins could be dirty and not making good contact. You could also connect a external power supply and then check to see if a press of the PTT switch works right.

    The schematic for the mic and the micro are readily available on the internet.

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