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Galaxy 94hp frequency display issue

Discussion in 'CB and Export Equipment and Accessories' started by Mk121, Aug 9, 2018.

  1. Mk121

    Mk121 Member

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    I have a 94hp that the first 3 digits of the display went out. The last two are still lit up fine. Checked the connections, ebreveryth seemed good. Any ideas? Thanks


     

  2. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    Go here...
    http://www.cbtricks.com/radios/galaxy/dx94hp/index.htm

    Locate PCB Layout and Parts section (scroll down to it)...

    locate Channel and Frequency Display - highlite and go to that page and review...

    More than likely a simple re-heat of solder Possible torn or broken solder joint but it's on the edge connector - so be careful.

    :+> Andy <+:
     
    Shadetree Mechanic likes this.
  3. Mk121

    Mk121 Member

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    Andy,
    Ok thanks I found the PCB layout. Would it be the r30 through r9 section that I should touch up first?
     
  4. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    (...going back and looking myself...)

    [​IMG]

    Bottom side
    [​IMG]

    Display digit board...

    [​IMG]

    Take your time on this - look over all this stuff for this is what I think you have - but is it what you ACTUALLY have?

    You should also look for PHYSICAL damage - dropped case - nicked corner - tapping on the board you hear a twang and see vibrating parts...

    IT those sections you will need to take a closer look...
     
  5. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    Do you see it yet?

    Bottom graphic, note the upper and lower sectional of the card, right where the two meet - in the center where upper and lower are - note the wording COM 1,2, 3 and COM 4,5,6 and 2DP?

    That is what I'm thinking...

    Back to the channel board with the "guts" for the frequency counter and display...

    Q 4 and Q5 poll - they rapidly turn the leads on and off....one on, the other off, the other is now on, this one goes off - cycle sort of thing...If you are missing one side and it seems the board connection is ok, these SMD parts may be the problem.

    :+> Andy <+:
     
  6. Mk121

    Mk121 Member

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    Yep I see what you talking about. That should be what I have. I will pop it open again later today and try to locate the area you are referring to. Will let you know what happens. Thanks
     
  7. Martian

    Martian Well-Known Member

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    As a sidenote to this if one of the resistors was at fault the symptom would be the same segment on several digits not working. You might see a 0 instead of an 8 for example on the digits that share that common.

    This is what is referred to as a multiplexed display.

    It's likely what @Handy Andy says. A broken track where the boards meet, the switch (transistor) itself or a support component. Possible but less likely is the microcontroller itself which if I recall correctly is a holtek MCU with a simple counter application.
     
  8. Mk121

    Mk121 Member

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    Well I did reflow a bunch of the joints. Including the ones Andy mentioned but still nothing. Just wanted to give an update.
     
  9. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    Ok, with power off, backprobe the front LED "Common" where you found that broken joint (if there was one) because if my hunch is right - the "bounce" or whatever physical strain that cause the broken traces - may have cracked more further along the chain - hence the continuity test and backprobe - and if it was on, may have caused Q4 or Q5 to fail due to the "jump" in load condition.

    If Q4 shorted, the display would be on all the time and show "overlay" of the next series of digits to display and you'd mostly see "888" kinda thing on your first three or last three because the two polling display toggles are "on" at the same time.

    But first check to see if the traces for COMMON for the groups - are good all the way back to Q4 and Q5 - they should show continuity all they way back to there...

    Usually how they number, Q4 may be your culprit - these transistors are a lot like a 2SA945 or a 2SA1015 - they are high speed switch NPN or PNP but they don't take kindly to "sudden" state of change on their loads there is a lot going on so they quickly fail under open no-load conditions due to the toggle event on their bases has nowhere to return. They are not high current sinking devices with built in power dissipation resistors...

    Heck even the "dim" function can make the parts fail - if someone played with it and or with a power supply trying to volt - these transistors are already pushed pretty hard...can cause this too.

    The Switch side of the board should have some holes in which to make up a "L" brace with any spare discrete leads laying around on the desk.
     
  10. TheRealPorkchop

    TheRealPorkchop Certified Sith Pimp

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    5BCE0A04-1DA9-4765-85D4-B614FB852B6E.gif
     
  11. Mk121

    Mk121 Member

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    Ok I'll be looking into Q4 and Q5 next time I get a look at it. Thanks
     
  12. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    Ok, remember that Q4 and Q5 are SMD - so the NPN or PNP can cross to a discrete part but the finagling you'd have to do is not easy.

    So if you have some SMD's or at least some NPNs' there may be hope...

    They're 2SC2712GR...
    Q4andQ5translateto.gif

    PDF attached of the Toshiba 2SC2712 series

    Look it over, and there is an outline in the PDF to help identify the leads.

    :+> Andy <+:
     

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