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TS-120 display

Discussion in 'Amateur Radio Modifications' started by 338_MtRushmore, Nov 16, 2018.

  1. 338_MtRushmore

    338_MtRushmore Well-Known Member

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    I have a Kenwood TS-120 that has all of the top and right top segments permanently lit at about 75% brightness. Would this be the display itself, or something else causing it? I am considering selling all of my old radios to fund a new radio that hopefully wont cause me so much grief. If I can get this TS-120 display fixed, I will probably keep it as a backup. Any ideas would be appreciated. 20181115_200859.jpg
    This is between bands when the display should be blank




    20181115_200850.jpg
    Tuned to 14.1111
     

  2. nomadradio

    nomadradio Analog Retentive

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    I'm at home, don't have the schemo at hand.

    (VERY short pause)

    Eventually I'll get used to having a fast connection. TS120 manuals are at mods.dk.

    Had a look at the schematic, and the 7 segments of the display are driven by IC16, a Toshiba-made chip that boosts the current output of the decoder chip IC15. It also protects the decoder chip from the high voltages on the digits.

    IC15 could have three outputs shorted, and IC16 could be okay. You could settle this question with a 'scope, but only if you sync the time base to the drive pulse for digit number 1.

    IC16 works harder, and also tolerates the high voltages that feed the VFD digits in the display. I think it's the more-likely chip to fail.

    IC16 is a Toshiba TC5066BP. No american-brand substitute I know of. And IC15, the less-likely of two possible culprits is a TC5022BP.

    Good luck finding either of those.

    If there is a substitute I haven't heard of it.

    ('nother short pause...)

    No lack of choices on Fleabay, turns out.

    73
     
    #2 nomadradio, Nov 16, 2018
    Last edited: Nov 16, 2018
  3. 338_MtRushmore

    338_MtRushmore Well-Known Member

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    I will have order some and prove you right. I have tried to learn some of this electronics stuff, and I just don't get it. Thank you for sharing your knowledge
     
  4. Chevboy0167

    Chevboy0167 Active Member

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    A good video on VFD problems. Not working a radio but the fundamentals are the same.

     
    338_MtRushmore likes this.
  5. 338_MtRushmore

    338_MtRushmore Well-Known Member

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    Any tips on soldering a new old stock IC? The flux I have is ratshack rosin. Does adding more flux and reheating help? I really don't want to mess up this board.
     
  6. 338_MtRushmore

    338_MtRushmore Well-Known Member

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    I guess I could be more specific. The solder is not wanting to flow in the IC legs. On the plus side, the display appears to be working properly now.
     
  7. Robb

    Robb Yup

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    If your iron is hot enough to ruin the board; then it is too hot.
    What kind of solder are you using?
     
  8. 338_MtRushmore

    338_MtRushmore Well-Known Member

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    650f, but I did try 700 to see if it made any difference. The solder is ratshack 60/40 rosin .032. I don't know how much heat theses boards can take, but I'm not looking to find out.
     
  9. nomadradio

    nomadradio Analog Retentive

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    Time to find some reliable solder. My favorite these days is Kester "44". Best alloy for that radio is 60/40 tin/lead.

    I got some bogus solder from RatShack decades ago, and never bought any from them again.

    This could be the root of the problem.

    73
     
    Chevboy0167 likes this.
  10. 338_MtRushmore

    338_MtRushmore Well-Known Member

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    I'm pretty sure it is just oxidation, but plan to get some better solder soon. She is all together and the display is back to normal. Thank you for the help getting this fixed, my eyes are much happier now.
     
    Chevboy0167 likes this.

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