Powering FT-818 with external DC

Discussion in 'General Technical Questions and Answers' started by N3AZ, Jul 3, 2021.

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  1. N3AZ

    N3AZ Ham Member QRZ Page

    I used the enclosed DC jack with wire and soldered a connector onto it, such that it connects to my switch mode power supply. I verified that the jacket has 13.8V and the center is the ground.

    I plugged it into my FT-818.

    Currently it reads "10.0V" on the top of the screen, and it also won't let me go into high power transmit mode (6W). It goes to "flashing 2 bars" which means it's throttled to 2.5W.

    I also noticed that it goes down to 9.3V when I transmit. Just now, after transmitting, I noticed it went down another nudge, to 9.2V. It's like it's using the battery pack, not charging it at all (like it should, while I use it) and it's not using the DC jack for anything.

    When I try to go into "Charging mode" per the directions, I get a quick double-beep, suggesting I made an error or it failed.

    How do I fix this? How can I verify that it's getting power from the DC jack? What am I missing?

    EDIT: I just came back to my rig after a while, and now it reads 9.9V at the top of the screen. So it would seem the battery is not charging for some reason, despite being on "External DC power". Or at least I should be!
    Last edited: Jul 3, 2021
  2. N3PM

    N3PM Ham Member QRZ Page

    "I verified that the jacket has 13.8V and the center is the ground."
    The center is usually positive.
    Mike N3PM
  3. KC7JNJ

    KC7JNJ Ham Member QRZ Page

    Sorry read the question wrong.
  4. W9WQA

    W9WQA Ham Member QRZ Page

    how many times have we seen extras discussing power supply hookup...??
    gotta say it...
    WR3V likes this.
  5. W2SGM

    W2SGM XML Subscriber QRZ Page

    The FT-817 does indeed have a positive center pin.
    Correct the polarization, but the radio’s protection diode is probably damaged. Hopefully nothing else got fried.
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I don't have an FT-818 but do have an FT-817ND and indeed the center pin of the DC input jack is positive. Unless Yaesu reversed that for some reason in the 818, sounds like the OP has it connected backwards.
  7. W9WQA

    W9WQA Ham Member QRZ Page

    at 25th and state,gemco electronix, ted and pearl ran the surplus store,chicago 1960's.
    pearl was heartless. a ham there was good at blowing stuff.
    she called him "w9pib" for put in backwards.
    hope noone with that call is offended but we have some pib's...!!!
    WA9SVD likes this.
  8. K2XT

    K2XT Premium Subscriber QRZ Page

    Why would the protection diode be damaged? That's it's job, to block current flowing. The radio is still working; he already said that.
  9. W2SGM

    W2SGM XML Subscriber QRZ Page

    It has a battery and appeared to be working on that based on his description of the voltage. I expect that correcting the polarity won’t restore external DC function at this point.

    The FT-817/818 is practically famous for getting cooked by reverse DC voltage, have a look at this thread:


    It’s possible damage was avoided if the radio was electrically isolated from anything else according to one poster’s account.

    There is also a TRXbench video on an FT-817 with reverse polarity damage that may be useful to the OP if there is any damage.
    Last edited: Jul 3, 2021
  10. KA9JLM

    KA9JLM Ham Member QRZ Page

    That would depend if the protection diode is in series or parallel.

    It must be series if no smoke occurred, Or fuse blew.

    That could have been a expensive mistake that most of us have done Once. :oops:
    K2XT likes this.

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