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Kenwood TS-940S display problem with a twist

Discussion in 'Radio Circuits, Repair & Performance' started by KA2JNF, Oct 30, 2011.

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  1. KA2JNF

    KA2JNF Ham Member QRZ Page

    Hi Guys!

    Hate to do this to you. I have a 7million serial Kenwood ts-940s that I have owned used for over 10 years.
    For a long time, ran great. Now if I leave it unplugged for several months, will get the dreaded dot dot dot display issue. If I re-set the processor a few times, and run it for awhile, it is ok again.

    I Played with it yesterday, and until I reset the processor, it was no good. Now it is running fine, breaking into all sorts of pileups on 10, 12 15 and 20 metersng. I thought this was an all or nothing problem, not an intermittent one. Is this the typical "loose connector" issue or does it sound like something else?

    I've been inside this rig, and am squeamish about moving boards around, and I know the 940 suffers from cold solder joints, but have not seen this spin on this problem before. Should I not worry about it, or is it something I need to delve into? and, any way to restore the print on the A=B and A/B buttons that is worn off?
    Thanks, Dave Ka2Jnf
  2. G4COE

    G4COE Ham Member QRZ Page

    Dots usually indicates pll trouble, usually out of lock. TS940/930 all same breed, I'd carefully do a resolder on all boards paying attention to the power regulator section, also check those mini rf connectors for tarnishing thus causing problems.

    Here's a old thread from QRZ.COM on the very issue.

  3. W0FRU

    W0FRU Subscriber QRZ Page

    You might check the condition of the lithium batteries. Low or dead batteries cause strange things to happen.
    Jack, K4FRU.
    KB3EPJ likes this.
  4. KA2JNF

    KA2JNF Ham Member QRZ Page

    thanks for the response, I appreciate the link. I suspected a cold solder condition of sorts, will study the link and see if I can handle it.


  5. G4COE

    G4COE Ham Member QRZ Page

    Further to K4FRU here's a jpeg of where they are along with the display.... I forgot about the LCD I assumed the main dial!

    I ought to have asked first.

  6. KA2JNF

    KA2JNF Ham Member QRZ Page

    Yes, it is the main display. the LCD sub display works fine, although I need to replace the grain of wheat bulbs with lcd's. I've run this radio on and off all day, and it has not even made a hiccup.

    and yes, It definitely could use replacement of the batteries, which was what I was hoping it would be, but apparently is not. these batteries are who knows how old, and could use replacement.

    any idea about re-silkscreening the a/b and a=b buttons, which the writing has worn off? this is the only cosmetic problem with my radio.
  7. G4COE

    G4COE Ham Member QRZ Page

    I've never tried it in my 930... but have done it in my Yaesu FT290, I used a hi-bright water clear 3mm LED with a 330 Ohm resistor (12V supply), the current was only 28mA, the lamp in these is a pain to change, hopefully changing the lamp for the very last time and it appeared a wee tad brighter and much cleaner looking - worth a thought! I'll certainly be trying it again should I ever have to change a lamp... stick to hi-bright water clear!

    One TS940 I repaired I could literally pull three bridge rectifier diodes out, they were that loose!

    I should have asked, my bad! But you confirmed the main dial then I would suspect a PLL unlock or problem. As far as I know all Kenwood's with a PLL fault will display a row of dots on the tuning dial.

    I don't know if there is anything here, but certainly worth eying over! KB2LJJ excellent article on the 940.

    For spare 'cosmetics' try this place, they are in the UK though.

    Last edited: Oct 30, 2011
  8. KA2JNF

    KA2JNF Ham Member QRZ Page

    I am torn between really getting my hands dirty on this. Like I said, I have looked at a bunch of the web pages on this one. I know that there is a lot of controversy on the 940 with the "reversed" transistors. for a 7 million serial rig, all the mods have not been done, I am wondering if it really is worth putting 500 dollars in repairs and shipping into it. I want to think I can do it myself, but am realistic about the fact that I am not just soldering a bunch of wires here. I am worried about separating tracings on the boards. If it came down to that, it would be a heck of a learning (and $$) experience.

    I have been inside the rig 2 times prior, and it is a marvel of how they got all that stuff to fit inside the box. Now to have to undo all that stuff, and fix it? that scares me.

    If I would decide to bail, who would you suggest to do the repairs?
  9. G4COE

    G4COE Ham Member QRZ Page

    Sorry, being the other side of the pond I can't say who's the best place to send it to... maybe someone on your side will advise.

    I guess these are the last of the 'serviceable' rigs, all seem to be going surface mounted components these days, they sure do look like dead bugs... all hot air and soldering paste.

    The service manual for it ought be available, the very last link, KB2LJJ I gave seem pretty informative on the PLL problem, just 'may' want a tweak. Try blowing some warm or cold air around the PLL and see if it drifts back to life.... don't want it too warm though, knowing my luck it'll drift the wrong way, hi!

    Hope you get it resolved, 73's

  10. KA2JNF

    KA2JNF Ham Member QRZ Page

    thanks for the responses. It is drifting to life, it is running well, just wondering if the other shoe will fall.

    I am putting my feelers out locally to see if I can find a qualified person to look into it. thanks for your help.

    Dave Ka2Jnf
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