TM-731a CMOS Reseting Itself

Discussion in 'Mobile Radio Systems' started by W5CNW, Nov 25, 2012.

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  1. W5CNW

    W5CNW Ham Member QRZ Page

    I have a Kenwood TM-731a. It likes to reset it's memory to factory default whenever it wants. I just replaced the CMOS battery, and I thought that fixed it, but I turned it on again last night, and it reset again! Do y'all have any suggestions as to what I need to do to fix this?

    Also, I'm actually using it as both a base station and mobile. It is mostly used as a base, and doesn't get turned off much. If I've posted this in the wrong forum, feel free to move the post.

  2. K0BG

    K0BG Ham Member QRZ Page

    Well, it is 20 years old! Two items. Are you sure the battery you used was a good one? Measuring just the unloaded voltage might not be a good indication, but in circuit it might. The other issue mat be the memory chip itself. Some of the old stuff just failed to hold a state after a while. It could be a cold solder joint too.
  3. W5CNW

    W5CNW Ham Member QRZ Page

    I did measure it outside of the circuit, and it read about 3.4-ish volts. I'll take it apart again and measure it in the circuit. If it reads good, does that mean the chip would be bad? And, if so, is it replaceable/fixable?
  4. K0BG

    K0BG Ham Member QRZ Page

    It is hard to say. It may be something as simple as a cold solder joint.

    The reason I mentioned the voltage... It isn't uncommon for a silver-ion battery (2035, 2016, etc.) to measure full voltage when using a DVM. The input to most DVMs is a FET with about an 11 megohm load. Put 500kΩ across the battery, and the voltage will drop quite a bit. If it is good, it won't.

    Sort of off the subject, but I remember all of the problems Gateway computers went through when the first introduced their flash-BIOS. They worked very well for several reprograms, but after that, they'd work for about a week before going south again. It was just the state of the art way back in the early 90s.
  5. W5CNW

    W5CNW Ham Member QRZ Page

    Well, I just measured it in the radio, and with a DVM I get 0.8 volts. With a o'scope I get .95. I guess the battery is bad. When I get a new one, would just putting a 500k resistor across it while I measure it be sufficient to test it? I don't want to have to install it, then find out it's bad.
  6. KA9JLM

    KA9JLM Ham Member QRZ Page

    I think it would be closer to 5K or 10k.

    If a new battery measures less than 3.6V out of circuit it may not be all that fresh.
  7. K0BG

    K0BG Ham Member QRZ Page

    Good point Don. You don't want to load the battery for very long,as the rating for those little guys ins't very much. That's why I mentioned a 500k, but a 50k might be a better choice. In any case, even .01 volts is too much drop.
  8. W5CNW

    W5CNW Ham Member QRZ Page

    I got a new battery today. This time I made sure to measure it before I bought it. It was slightly over 4.1 volts, and showed now drop with a 10k resistor across it. I'm about to go install it.
  9. W5CNW

    W5CNW Ham Member QRZ Page

    I just finished putting in the new one. It measured 3.4-5-ish in the circuit. Which is much better than .8!! Hopefully this will fix it. I'll post back here if it doesn't.

  10. W5CNW

    W5CNW Ham Member QRZ Page

    It didn't fix it. . . Where should I start trouble shooting?
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