In my experience, the Icom IC-746/756/PRO-series are quite susceptible to electrostatic discharge (ESD). And a common failure is the “Remote” port (or CI-V port).
Usually, one or two surface-mount components are affected: a transistor and/or an RF-bead/choke (or jumper).
Here are the components most affected in each model:
IC-746: Q1702 and/or W1261 on Main Unit
IC-746PRO: Q1941 and/or EP760 on Main Unit
IC-756: Q802 on Main Unit
IC-756PRO: Q3772 and/or W701 on Main Unit
IC-756PROII: Q3772 and/or W701 on Main Unit
IC-756PROIII: Q3772 and/or EP701 on Main Unit
Here are a couple of tests to determine if the CI-V port has indeed failed:
Measure for continuity between the ground side of the CI-V connector and the chassis. It should be close to, if not, zero-ohms. Otherwise, the RF-bead/choke (or jumper) may be open. Although, another possibility is the ground pin of the CI-V jack has a cracked solder-joint, due to mechanical stress on the connector.
You should measure about 4.5VDC across the CI-V port, with no interface connected. If the voltage is much lower (assuming the RF-bead/choke is OK), then the transistor may be at fault.
Here are the components in the IC-756PROIII:
MMZ1608Y102B SMD Ferrite Bead (EP701, under Main Unit)
2SC4081T106R SMD Transistor (Q3772, topside of Main Unit)
Both of these components were available from Digi-Key and Mouser at the time I posted this.
Here are component locations for the IC-756PROIII:
NOTE: If you don’t have the skills or equipment to work with static-sensitive surface-mount components, please leave it to an experienced technician.
Mike Nadeau – N1EQ
April 28, 2014