IC-7300 Clock Battery Failure

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

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  1. KH6AQ

    KH6AQ Ham Member QRZ Page

    I haven't read all the posts but this is interesting. My analysis of the circuit:

    IC-7300 schematic: page 8 left-hand side
    https://www.hamradio.co.uk/userfiles/file/IC-7300_Schematic_Diagram.pdf

    Clock IC: RX-8803LC, typical current 0.75 uA, max 3.4 uA
    https://support.epson.biz/td/api/doc_check.php?dl=brief_RX-8803LC&lang=en

    Cell: ML414HIV01E, nominal 3.1-2.0 V, 1.05 mA-h to 2.0V (see graph), 72 recharge time at 30 uA
    https://media.digikey.com/PDF/Data Sheets/Seiko Instruments PDFs/ML414H_E.pdf

    Diode: L1SS400, 0.4v forward drop 1 uA, 20 nA reverse current
    https://html.alldatasheet.com/html-pdf/135337/LRC/L1SS400T1/118/2/L1SS400T1.html

    Resistor: 3.3 k ohms

    Notes (25 deg C = 77 deg F)
    The circuit cannot fully charge the battery. It can charge it to 2.9 volts which I estimate to be 80%.
    The circuit cannot overcharge the battery.
    The diode and 3.3 k resistor are used together to meet safety agency approval for single component failure with no battery leakage.
    The IC can discharge the battery to 1.6 V or lower.
    The diode reverse current does not significantly discharge the cell (it is 1/40 the typical clock IC current draw).
    The calculated operating time for max to typical IC current based on 80% charge is 240-1100 hours, or 1.4 to 7 weeks.

    My IC-7300
    My IC-7300 was stored unpowered for 6 months and lost its clock setting. I reset the clock.
     
  2. WA9SVD

    WA9SVD Ham Member QRZ Page

    I don't know about battery failure. I have Kenwood radios (desktop) and Standard H-T's that keep memory and such for at least 10-20 years at a time. My Standard dual band H-T had a battery replacement after 25 years, as "preventative maintenance," since it's "chest had to be cracked" for another (minor) problem. For a battery to die in only a few years (or much less) is either a component failure, OR very poor design. (Of course, it DOES keep the techs at the major manufacturers employed...:(:mad: (AKA "job security".)
    Even my computer batteries last at LEAST 10-15 years. Even if not used for that period of time.
     
  3. KA9JLM

    KA9JLM Ham Member QRZ Page

    It looks like some IC-7300 radios use a capacitor for backup. Was there a REV change ?

    upload_2019-11-23_21-55-35.png
     
  4. WA7F

    WA7F Premium Subscriber QRZ Page

    So my 7300 has been in a box without power for about 18 months. After reading this thread I connected it to 12V battery. I did not attempt to power it on, just left it connected to power for a week.

    Fast forward one week; I just powered it up and it seems Ok. Disconnected the 12V battery for a few minutes, reconnected and it’s still Ok. Will disconnect from power for a week and try again.

    This is an early production unit. Bought it shortly after the 7300 was released.
     
    Last edited: Dec 16, 2019
  5. W9WQA

    W9WQA Ham Member QRZ Page

    i did not read all pages of this thread,jfwiw...
    first,i have a 7300,2 yrs and left the ps on without thinking. clock is good . i do turn off at times for a day.
    i dont want a dead batt and i dont want to worry either
    heres an idea.first to see if the concept makes sense,then if so, how to do it .
    add a small rechargeable 12 v batt to the power input permanently to maintain the internal batt. use a resistor to limit charging from the power supply when on.
    when off the small 12v batt would trickle thru the "500' ohm limiting resistor to keep the internal batt alive,forever, but not run the radio! note, picked the "500" out of the air!, not good...

    it could be lower volts with a limit resistor appropriatly sized,like 6v.
    if that could be done, is it feasable?
     
    Last edited: Dec 18, 2019
  6. WA7F

    WA7F Premium Subscriber QRZ Page

    I think the moral of the story is to just use your 7300 once in a while. My 7300 hasn’t seen much use since I bought the first Flex 5000 but, I like it too much to sell it.

    If you are really worried about charging the clock bat and you don’t intend to power it up once in awhile just put a timer on a power supply so it turns on for an hour or two per week. Apparently, the 7300 does not need to be powered on to charge the clock battery.

    Also, I don’t think it’s clear if this affects all 7300’s. I would be willing to bet that some of the batteries are weaker than others. Maybe Icom got a bad lot during production. Time will tell.
     
  7. KA9JLM

    KA9JLM Ham Member QRZ Page

    From the pictures that I seen, Some use a capacitor, Some use a battery.

    The capacitor designated on the board is "C"
     
  8. W0AEW

    W0AEW Ham Member QRZ Page

    What is the clock used for? Never had a rig with one.
     
  9. W9WQA

    W9WQA Ham Member QRZ Page

    anybody have any thoughts on my idea?.
    this is obviously a problem to be solved. i offer just one solution.
    or, can we wire in a socket for a better battery . inside there is plenty of room.
    lets focus on fixing, not putting our heads in the sand !!
     
  10. W9WQA

    W9WQA Ham Member QRZ Page


    back in the 50's when they used toooobes,hallicrafters had an analog clock up in the corner. hams need time more than anyone.
    its a great idea.a guy had an ht with one!
     

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