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Icom EX-314 Solutions

by Gregory Beat, W9GB

The Icom radios (Icom IC-751, IC-751A) of this era have a well-known and well-documented problem with the original ICOM EX-314 board that plugs into the logic board mounted in the lower part of the radio.

In the early 1980's, Icom introduced the IC-745 transceiver and R71A short-wave receiver. Shortly after this, the IC-751 (HF), along with the IC-271 (VHF) and the IC-471 and IC-1271 (UHF) transceivers were also available. All six models were frequency synthesized and microprocessor controlled using the same replaceable plug in memory module.

It didn't take long for someone to discover that a defective or dead lithium battery on the memory board caused the radio to become inoperative. The Icom module stores the radios 32 memories along with important data that's used by the microprocessor's operating system. When the backup battery fails, the memories and data are lost and the radio no longer functions!

There are a number of solutions and replacements boards using modern components and better designs that correct this problem! The replacement boards are superior -- in that you never have to worry about this design shortcoming regarding "radio setup data" again!

Icom selected the RAM based system to support multiple versions for shipment to other countries.

In the 1980's, small inexpensive RAM memory chips were available and before shipping the radio, Icom used computer controlled programming fixtures to load the memory module with the appropriate version. Back then 32K EPROM's carried a high price tag and low power, battery backed, 32K Random Access Memories were not available.

The lithium battery had a projected life expectancy of 10 years and some batteries, at room temperature, can last longer than 15 years. Unfortunately, Hams don't always operate their equipment at room temperature at a fixed location. Depending on the environment, mobile or portable operation for example, the battery life can be reduced.

TODAY, there are replacement boards for these radios that contain a Read Only Memory (ROM) that permanently stores the radio's important data and a battery backed (lithium-ion cell) Random Access Memory (RAM) that stores the radio's 32 memories.

TWO solutions or approaches to the Icom EX-314 board problem:

  1. Replace the battery -- while NOT losing the critical radio information.

  2. Purchase a modern replacement board -- and no longer worry about the volatile RAM memory.

BATTERY REPLACEMENT and/or reprogramming links:

  1. ICOM AMERICA - RAM Card Backup Battery Replacement Instructions for 271, 471, 1271, 745, 751A, R71A

  2. Download the Adobe Acrobat DIY instructions (with useful photographs)  [mirror]

  3. Wilco Electronics has a service to perform this service function for radio amateurs

  4. N2CBU - RAM Module ReprogrammingREPLACEMENT BOARDS

  5. Roberto Nardo, IK2RND - Original EPROM/RAMBOARD

  6. EB5AGV's Icom RAM Board Resources

  7. Wilco Electronics - ICM-1024B

  8. Piexx - ICOMPROM

  9. Installation documentation for the Piexx solution

Contents copyright  2004-2018, G. Beat W9GB.
Page created by A. Farson VA7OJ/AB4OJ.
Last updated: 09/25/2019

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