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MFJ-1261 and IC-7100 PTT Issues

Discussion in 'General Technical Questions and Answers' started by N8PDX, Aug 9, 2020.

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  1. N8PDX

    N8PDX XML Subscriber QRZ Page

    Okay, I'm officially stumped. I purchased a MFJ-1261 one mic-two radio box so I could use my Heil iCM mic on both my Icom 7100 and 7300. The 7300 uses a 8-pin barrel, just like the iCM, but the 7100 uses a modular connector. I referenced the pin outs for both radios and reconfigured the jumpers on radio B (7100) since the pin outs for the 7100 and 7300 are slightly different. The 7300 works perfect, but the 7100 changes the channel up every time I press the foot switch. I even completely disconnected the jumpers for pin 2 (freq up/down) on the 7100, but it still does it. If I plug my factory mic into the MFJ box the mic PTT works fine, and the radio operates normally (suggesting my jumpers are correct) but the foot switch still changes channels.

    I've triple checked my jumpers and even continuity tested them and everything appears correct. I've probably spent 4 hours fiddling with this stupid issue, so now I come to the pros. Thank you in advance for any help.

    Any advice would be greatly appreciated.
  2. N8PDX

    N8PDX XML Subscriber QRZ Page

    Well after hours with a multi-meter, I finally figured it out. The issue was that the MFJ documentation fails to mention that because the modular connectors are upside down compared to Icom pin outs, the Icom pinout needs to be reversed. So pin 1 = pin 8 and so on... All I can say is that this box and its poorly written manual are challenging at best. Be sure you’re extra careful with the jumpers as you can put 8v DC onto any lead easily by mistakenly placing a jumper. Attached is a pic so those of you wanting to use 1 mic with the Icom 7300 (Radio A) and 7100 (Radio B) have an example of what worked for me.

    Attached Files:

    K5EMG likes this.
  3. K5TGS

    K5TGS Premium Subscriber QRZ Page

    Jason, you are a genius! I am using your setup for the IC-9700 (A) and IC-7100 (B). Thanks you!!
  4. N8PDX

    N8PDX XML Subscriber QRZ Page

    I'm happy I could help!
  5. NS3K

    NS3K Ham Member QRZ Page

    Just purchased a 1261. Thanks a million for your info . I would have probably returned it. Now I can us my SM-50 on my 9700 and 7100.

    Jim, NS3K
  6. K7JQ

    K7JQ Ham Member QRZ Page

    Years ago, I had the same problem with a Icom IC-706 MK II G (modular) and IC-746 PRO (8-pin round), and never could figure it out, despite contacting MFJ for help. Where were you when I needed the solution:):)?

    Bob K7JQ

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