TM742A battery replaced – finally

By way of a short history lesson, 16 years ago my employer decided I was surplus to their requirements and gave me extra money to finish up. I took some of that money and invested it in a new Kenwood TM742A 6m, 2m & 70cm mobile rig. Since then I have used this rig a lot, and when I was doing field work it was in the car and in use every day. It has been to every SRESU activity I have done since 1996 and has never let me down.

Inside these rigs, like so many rigs of that era, is a small 3.0 Volt lithium battery that backs up the microprocessor, channel memories and such.

Lithium batteries are generally regarded as being good for about 7 to 10 years. After that time they have discharged too much and the memories start to become corrupt. I have even read of these batteries leaking and damaging the circuit board they are on beyond repair.

In July 2006 I decided that 10 years was a good length of time for the battery in my TM742A so I bought a new battery from Jaycar and resolved to replace it. The radio had been working fine with only an occasional hiccup but it was something that needed to be done.

2006 came and went; battery not fitted. 2007 and 2008 came and went; no battery fitted, 2009 and 2010 came and went; battery still not fitted.

Today I had planned to get on the roof and look at my dipole antenna but it was raining. So I decided to have a go at fitting the ‘new’ battery into my TM742. The TM742 group is a great source of information and I had downloaded instructions on how to replace the battery so I was fairly confident.

The task flowed well, as described in the instructions and, apart from my battery being slightly different from the existing battery, went without a problem. I even added a piece of paper with the date on it so I remember when it was done when next I have to change it.

Hopefully I will get 5 or more years out of this battery. Although to be fair it has already sat on the shelf for 5 years and if it has only a 7 year life then it won’t be long before I am doing it again.

Old battery in situ on left side of chassis

Board with new battery – note the added black wire (on the negative side of the battery)


Solder points for battery
Solder points for battery

New battery on left side of chassis


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