Memory Backup Mod
Submitted by Terry

This picture shows a modification I made to my R2000.  Kenwood and other manufacturers use large value, low voltage capacitors as memory backup power sources instead of the more common Lithium backup. I have a friend who owns his own 2-way repair shop.  One of the 70cm radios comes with a throwaway circuit board that was used during factory setup.  These boards have 0.047F (yes FARRAD!) 5V capacitors on them.  I read about doing this in the rec.radio.scanner newsgroup several years ago, and modified my Icom IC-28A 2-meter transceiver shortly after that.  The Lithium cell in the IC-28A had failed and I needed to use the radio that night.  Unfortunately, I had no spare on hand.  I added a 0.047F capacitor and the IC-28A has been working ever since.  I have no idea exactly how long the capacitor will keep the memories alive, because I've only had the IC-28A off and disconnected from the power for about 6 months at most.

After purchasing two Lithium cells, both of which went flaky in a matter of days, I decided to switch to a capacitor.  I chose to use 2 of the 0.047F caps for a total of 0.1F.  I have several 1F units, but they are just too large to fit on the circuit board.  I wired the caps in to the post where the Lithium cell had been and added a string of two 1N914 in series between the positive terminal of the cap to the +5 volt rail.  That will keep the R2000 memory alive for at least 4 days, the longest time my R2000 has ever been disconnected from the power.

A more reasonable person might have decided to add a battery pack with 3 “AA” NiCads.  But I like the idea of using parts from one Kenwood radio to repair another.  

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