IC-7300 Clock Battery Failure

Discussion in 'Radio Circuits, Repair & Performance' started by NZ4J, Jun 25, 2018.

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  1. NZ4J

    NZ4J Premium Subscriber QRZ Page

    Greetings:

    I was having the same issues as others have reported regarding clock loss when the IC-7300 has not been attached to power (rig on or off) for long periods. The rechargeable lithium battery discharges and allows the clock to reset its time.

    After attaching power for two weeks, I noticed that the clock would loose its time after about four (4) days without power.

    Deep Discharge Causing Damage?
    It occurred to me that the deep discharge of the battery could have damaged the performance of the battery. This is common with LiPo batteries that get discharged below the minimum cell voltage.

    Not being sure of the chemistry, I simply opened the case and measured the battery after a long charge period. ("Long Charge Period" is two (2) days in this case.) In circuit, the battery measured 2.46VDC. The charge should have been closer to 3.0 VDC.

    I ordered a new battery online. DigiKey had stock to ship.

    The 4mm battery is soldered to the board and is not trivial to remove. I am just fair at the small parts removal process but with care I was able to remove the battery without making a mess of the board traces.

    I removed the old battery and measured its remaining charge. It was below 2.2VDC.

    I powered the rig without the battery and measured the voltage that would be applied to the battery. It is slightly above 3VDC. I surmised that the charge circuit was functional. The rig supply voltage was 13.8VDC.

    I installed the new battery and started the charging process. The battery voltage as received from the vendor was about 2.64VDC. This is similar to a LiPO storage mode charge - not fully charged. After power was applied for about 9 hours, the battery voltage was 2.99VDC. I will check the voltage after 24 hours and report back.

    My guess is that leaving the rig unattached to power, regardless of whether the rig is turned on or off, will cause the battery to eventually drain below a certain charge that damages the battery. If your ic-7300 has been un-powered for over 6 months like mine was, it is possible the battery has diminished capacity for holding up the clock.

    Unfortunately, due to a transient significant health issue, my rig was isolated and alone for obviously too long...

    Cheers and 73

    Jim
     
  2. WC5P

    WC5P Premium Subscriber QRZ Page

  3. NZ4J

    NZ4J Premium Subscriber QRZ Page

    Hi Paul.

    Yes. Very helpful reference material for those folks that that do not already have that guidance.

    It is important to realize that even with that guidance, albeit late for many people who were early ic-7300 adopters like myself, , the battery can fail. Following the UK service department advice after the battery has failed will not result in reliable or long lasting preservation of the clock.

    Thanks again for your contribution.
    Best regards/73

    Jim
     
  4. KF5FEI

    KF5FEI Ham Member QRZ Page

    No way to put in a battery socket and use easily replaced batteries?
     
  5. NZ4J

    NZ4J Premium Subscriber QRZ Page

    Hi John. Your suggestion to examine that possibility is intriguing. There are two characteristics of the existing circuitry that possibly need to be addressed carefully.

    1. The current schematic illustrates a "charging circuit" that takes power from the external 13.8VDC power supplied to the rig and uses it to apply current to the small battery. There is a blocking element that prevents the battery from supplying the "world" through that power connection. The battery has a (//sarcasm warning) whopping 1mAh capacity. It would be easy to substitute a typical lithium cell that is not rechargeable in its place. The issue is that those easily replaceable lithium coin batteries (CR2016, CR2032, CR1025, etc.) are not normally rechargeable. Applying voltage to those types is probably highly discouraged.

    2. Looking further at Mouser and other sites, a replaceable rechargeable Lithium coin cell battery can be found quite easily. Acquiring the socket holder is also possible. And, of course, a much larger capacity battery (with commensurate longer charge times) with longer holdup times and reduced probability of over-discharging could be utilized.

    The installation area seems to have ample space for a battery and holder.

    The installation will not be "factory perfect" from a design point of view. Folks will need to look inside their rigs to see what innovative solutions can be discovered. There are a lot of creative folks out there.

    One possible solution is to attache the battery holder to the bottom panel (outer cover of the radio) and supply a set of wires that has a plug/socket combination so that the bottom panel can be completely removed.

    I will be making battery measurements this evening using the standard replacement battery. I will post the results - success or failure. I will run some endurance tests over the next week to determine the battery voltage profile over time.

    And...

    Here is a CR1220 coin cell holder that might fit on the bottom cover or ???
    https://www.adafruit.com/product/1868
    Add wires and attach to the main board after removing the existing factory battery.

    According to the Panasonic Data Sheet, the ML1220 is a 17.0 mAh 3V rechargeable coin cell that would fit into the coin cell holder above. The battery is available for a pressure contact application such as is required for an easily replaceable installation. Its nominal current profile seems adequate for the clock chip.

    I would have to order one of these batteries to be sure it fits the holder. I may do that later this week. I am interested in a more user friendly implementation.

    Thanks for the suggestion.

    73
    Jim
     
  6. NZ4J

    NZ4J Premium Subscriber QRZ Page

    It is now more than 24 hours after replacing the battery and it has charged to about 3.02 VDC. Obviously, the original battery which only charged to about 2.46 VDC, regardless of time with power applied, was degraded, possibly by too deep a discharge.

    John, I will be ordering the battery holder and battery as identified in the prior post. I will update this thread as soon as I have further details.

    Best regards, 73, Cheers!

    Jim
     
  7. KF5FEI

    KF5FEI Ham Member QRZ Page

    Reason I suggested this, is back in the dark ages, computers had BIOS batteries that had a limited life. Some manufacturers used to put a header on the board to allow the use of an external battery, once the factory one failed. The replacement battery was secured with double-sided tape.
     
  8. WC5P

    WC5P Premium Subscriber QRZ Page

    I wonder if there is an actual specification for how long the clock should stay running after 48 hours charging. I bet that’s a question that would generate some tap dancing.
     
    WB1E likes this.
  9. KA5IPF

    KA5IPF Ham Member QRZ Page

    I don't have a clue about the current draw of the battery in the Icom but the Kenwood's that have battery back-up typically draw 2-3 uA so a 1ma battery is plenty. If you knew what the clock chip is you could look up the current draw.
     
  10. NZ4J

    NZ4J Premium Subscriber QRZ Page

    Clifford,
    A quick check on the part (RX-8803LC) reveals that it has similar current requirements and has a normal operating voltage of 1.6VDC up to 5.5VDC @ 2.1-3.4uA.
    Using the low voltage specification, it is probably not difficult to determine how long this clock will be maintained by that 3.0V 1mAh cell.

    I am going to test the replacement factory cell and see how long it takes to drop from 3.0V to 2.0V. After that experiment, I will add a CR1220 coin cell holder inside the radio and install the rechargeable battery that can be easily replaced when it fails.

    I hope all the IC-7300 owners are powering their rigs before the battery degrades. This sure interferes with being on the air with the latest sun spot numbers increasing slightly...

    73
    Jim
     

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