Saturday, November 25, 2017

Icom IC-R7100 and its clicking noise

Some time ago an Icom IC-R7100 arrived to my shack. It's a nice receiver and works surprisingly well but almost the very first time I powered it up an annoying feature came up: every time the squelch opens or closes, It produces a clicking noise.

It is ok for the first five minutes but it can be irritating after that.

The cause

The IC-R7100 had an interesting feature for its time: a remote recording output. This output is intended to drive the motor of a tape recorder, so when the squelch is closed the tape recorder's motor is off. When the squelch opens, the IC-R7100 closes a relay and its contacts, through the remote recording connector, turns on the recorder's motor. In this way you can record tons of hours of listening into a 60 minutes cassette tape, automatically removing the silences between transmissions.

This relay is activated as soon as the squelch opens, and deactivated about 1.5 - 2 seconds after the squelch closes, making that annoying clicking sound. In its time this remote recording function was a nice feature but today is totally obsolete. If you want to record something from your IC-R7100 receiver you will use a computer and a modern program with VOX operation (for example Audacity) making this relay useless and an unwanted source of noise.

The cure

The cure is very simple: just disable that relay.

Location of R40 in schematics

The relay is RL1, located in the main unit. It is driven by Q4 through R40, a 68 ohms current limiting resistor. All these components are located in the upper-right corner of the main unit PCB (with the frontal facing to you). The easiest way to disable RL1 is to cut one leg of R40.

Location of R40 in main unit.

Take a look into the service manual to access into the main unit: It is located just in the middle of the receiver and it is not accessible neither removing the top cover, neither the bottom one.

After this modification no more clicking noises with the benefit of a new output connector ready for other purposes, for example FM discriminator output.

Miguel A. Vallejo, EA4EOZ

No comments:

Post a Comment