Have the Kenwood TM-V71/V710 Filter Issues Been Resolved?

Discussion in 'Mobile Radio Systems' started by NR8Q, Jul 9, 2012.

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  1. NR8Q

    NR8Q Ham Member QRZ Page

    I'm thinking about purchasing a TM-V71A. The filter death issue definitely
    concerns me. However, I've seen a couple of posts online claiming that the board
    was redesigned and the filters are now protected from DC. Supposedly, this
    change was rolled into production sometime in 2011. I can find no real
    information to prove this is true

    1) Does anyone have any proof this really has been fixed in current production

    2) Does anyone know how to identify a radio's production date?

    Thanks for the help,
    TY (NR8Q)
  2. K0BG

    K0BG Ham Member QRZ Page

    I must live under a rock, because I've never heard of this issue! And a search on Google brought up nada!
  3. M0GVZ

    M0GVZ Ham Member QRZ Page

    Its been a monumentally big issue on the TM-V71 and subsequently TM-D710.

    OK in short....

    Kenwood didn't put any DC blocking on the TOKO ceramic filters they use. As a result, they failed due to electro migration. People modified the board by cutting the tracks and inserting capacitors. Eventually around 2010, Kenwood finally admitted to the problem, modified the board and added blocking capacitors to the filters.

    More here:


    Solution for pre-revised boards
  4. K0BG

    K0BG Ham Member QRZ Page

    The term, electromigration, refers to the gradual displacement of metal ions in the crystalline structure of a conductor. I've heard of such a process in quartz crystals!

    I looked again for a reference to this issue on Google, and two of the Kenwood blogs. Again, I get nothing. Can you give me a link to an article about this issue?
  5. NR8Q

    NR8Q Ham Member QRZ Page

    eHam doesn't allow linking to individual reviews so the best I can tell you is to go read the reviews. You'll find a good sample of people with the problem there. Also, just googling "Kenwood V71 filter problem" brings up 5 different links about it just on the first page of google results. You google-fu is weak, my son :lol:
  6. K0BG

    K0BG Ham Member QRZ Page

    I'm not convinced!

    Crystal filters certainly aren't my cup of tea. Nonetheless, I remember reading about a ceramic filter issue similar to the one described SV8YM's site. I don't remember the author for sure, but the problem was traced to crystal contamination, not electromigration.

    I don't deny that Kenwood might not have DC isolated the filters. That fact may have indeed exacerbated the issue, but again I am not convinced that electromigration was the real culprit.
  7. NR8Q

    NR8Q Ham Member QRZ Page

    Frankly, I don't really care why the filters were failing. All I'm interested in is wither a radio I could buy today has an unusually high probability of having the issue.
  8. M0GVZ

    M0GVZ Ham Member QRZ Page

  9. K0BG

    K0BG Ham Member QRZ Page

    Conor, that is the one I read. I know this sounds like I'm beating a dead horse, but I'm still rather leery about electromigration being the real cause. The main reason I'm skeptical, is not only the distance of the migration path, but the minute current and voltage levels present. I wish I could locate the article I read a couple of years ago about crystal contamination.
  10. KZ9G

    KZ9G Ham Member QRZ Page

    The issue was the bad run of filters. It did not help with the design of having voltage on the filters. There is a list of affected serial numbers that have the bad filters floating around (I believe on the yahoo group). There have been no known issues after they got away from the bad run. There is a rumor that they changed the design and the current production radios have the blocking caps installed. I cannot verify this due to not having a radio that is current production. I have two that are in the affected range and one has gone bad and the other is fine.
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