Icom IC-735 VFO Encoder Repair

Revised 1-8-2018

The Icom IC-735 HF transceiver was produced in the late 1980's. It was a very popular radio then and is still highly regarded, as evidenced by reviews found here and other places online.

My IC-735 was purchased new and it experienced heavy usage as my primary rig. Even after three decades it still sees occasional operation as a backup radio. It is definitely a keeper.

Recently my IC-735 developed a problem with its main tuning (VFO) sensor/encoder. As the knob was turned to increase frequency, the displayed frequency would change erratically and sometimes jump to a lower frequency.

Some online research revealed this is a fairly common problem. Usually it is due to one or more failed phototransistors on the encoder printed circuit board that are obsolete. Unfortunately, replacement encoders are no longer available from Icom. If the encoder is otherwise mechanically sound, then the problem is fairly certain to be just an encoder electronics failure.

SultanTronics sells an assembled and tested replacement encoder printed ciruit board for the Icom IC-735, IC-761, IC-765, IC-781, IC-275, IC-375 and IC-475 radios as seen here. An order was placed for one of these boards. Bruce, W7BCW of SultanTronics provided a tracking number and the board arrived two days later.

Here are a couple of photos of the SultanTronics board.

This board was installed in my IC-735 as described below.

The IC-735 top cover was removed (12 screws total including four at the speaker.) Next, the four screws securing the PA unit were removed and the PA unit was set on its side next to the radio.

The encoder connector was unplugged from the main board.

The VFO knob was removed using a 2 mm Allen wrench to loosen the setscrew.

The four encoder mounting screws were removed and the encoder was slid out of the front of the radio.

Here is the original encoder assembly after removal from the radio.

The original encoder wire harness was removed and soldered to the SultanTronics board.

The orignal encoder circuit board was replaced by the SultanTronics board.

Installation was accomplished by performing essentially the same steps in reverse order.

The SultanTronics board corrected the problem and the radio is now working perfectly again. I am very pleased with the SultanTronics solution.

Contact Information

P.O. Box 1707
Sultan, WA 98294

Phone (360) 793-9513

Email bruce (at) sultantronics (dot) com


I have no affiliation with SultanTronics other than as a happy customer.

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