Icom IC-705 USB-C/SEND Control Board Upgrade
Important Update 4/28/2026
About
This is a drop-in replacement control board (Connect Unit B-9128B) for the Icom IC-705 radio. Designed by Ben (KD9LJF), it is an easy upgrade for any IC-705 radio.
Installation Guide
We have a step-by-step picture installation guide on our website: Icom 705 USB-C/SEND Board Installation Guide
You can also find a video explanation and overview here: https://www.youtube.com/watch?v=H1DPDUeaDfw
USB-C
The upgraded control board has a USB-C port that retains all of the original port's functionality (including computer data). This port is just a connector swap and works identically to the original board. This means that it does not add any USB-C Power Delivery (PD) features. You can still charge the radio through the USB connector with any USB-C charger, but it will still only charge at 5V and around 7.5W from the charger with the radio turned off.
SEND line
The SEND/ALC circuit has also been upgraded for additional protection for connecting external amplifiers. The original board from Icom was only capable of switching less than 30mA of current on the SEND line. Connecting an amplifier that operates by switching 12V to ground would likely fry your original board as it did for mine. Our new control board has upgraded MOSFETs for the SEND line that can switch up to 1.0 amp of current. We also added a Zener diode to protect against voltage spikes above 16V. Our upgrade to this circuit makes your 705 compatible with most 12V amplifiers without additional adapters other than the TRS 3.5mm cable.
Known Amp Compatibility List
Help us build an amplifier compatibility list! Message us with the amp model you've tested with the upgraded board. (Note, most 12v amps will be supported. You amp will likely work, even if it's not on our list.)
So far, we have tested the following amps:
- Homebrew 12V amp
- TenTec Titan
- Xiegu XPA125b
- Xiegu GPA100