I received a message from a fellow Ham asking for some help to get digital communications up and running. His main issue was that the USB/PC interface would not key the radio.

I made an visit to his shack and together we did some testing. First we checked to make sure the interface was actually providing a ground to key the radio. We then tested to make sure all of the settings in the radio were correct and there wasn’t something that would inhibit the radio to be keyed at the data jack. Finding nothing, it was a trip to the shop.

On the bench and under better lighting, the data jack appeared to have had some serious use in the past.

Picture showing wear to data jack

A review of the schematic in the service manual. I found the likely places to start my troubleshooting.

I opened the radio, and noticed right away that I was not the first person to take the covers off. Someone had made some sort of modification to the main board. I added this to my “clue 1” placeholder.

Picture showing the covers removed
Pointer showing a wire modification on the main board

It wasn’t long before I noticed even more trouble. Someone had removed (ripped it off the board) the diode that feeds the PTT circuit. I also found a shorted transistor and a resistor that was half the rated resistance value.

Picture showing missing Diode
Picture of Schematic
Picture showing faulty Components

After some discussion with the owner he decided it wasn’t going to be worth the cost to make the repairs to this radio and the fact someone had already made some potential “fixes”, he would just use the radio for voice and as a backup. It’s hard to speculate what could have happened to the data port that necessitated the removal of the diode and the damage to the other components. Whatever happened, the poor little parts didn’t survive.

By Jim

Over 30 years in automotive repair. I worked as a Technician, Shop Foreman, Service Manager, and Fixed Operations Manager. I obtained my amateur radio license in 1991 and really enjoy the hobby! I love to work on and repair anything electronic. My desire is to constantly learn something new!

2 thoughts on “ICOM IC-746PRO”
  1. That is the same radio that’s I have. My first and only one. Now I have some of its insides…. and to never have to see more. Cooloi

    1. Very cool steve! Yeah, I do remember seeing that radio at your place. Hopefully, you won’t even need to look instide! 🙂

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