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Galaxy 959 shorts out a few seconds after power up

Discussion in 'General CB Services Discussion' started by Cobra999, May 1, 2021.

  1. Cobra999

    Cobra999 New Member

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    I've already beat myself up over this but at the time didn't realize it would be a problem. I was testing SSB radios about 10 ft apart, one in mobile, one base on a 16ft antenna on the roof. When trying to clarify and get my voice to sound good (admittedly i was showing my daughter how it worked) my galaxy went dark (she said). It blew the breaker on my DC power supply.

    So right now, any time we turn the DX on, on AM it might sit there RXing fine for a bit, but if I let it sit or try to TX, it will pop the fuse again. If I turn it from AM to LSB/USB, it the RX light does not go on at all, and the freq counter will dim for 3 seconds with a hum coming from speaker and the fuse will pop every time.



    Where should I begin to look?
     
    #1 Cobra999, May 1, 2021
    Last edited: May 1, 2021

  2. Cobra999

    Cobra999 New Member

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    #2 Cobra999, May 1, 2021
    Last edited: May 1, 2021
  3. Handy Andy

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

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    upload_2021-5-1_13-5-4.png
    any sign of a short or bad capacitors in TX - when it TX's can now be bad,
    the bad cap (or Diode) can cause a short and
    blow fuses in TX mode.​
     
  4. Cobra999

    Cobra999 New Member

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    I will check cont shortly as you showed, thanks! I did reseat the tab/chassis just to make sure something wasnt shorting out there.

    The problem has evolved.. Now if the radio is turned on at all, the leds come on for maybe 3 seconds, i hear a buzz from PSU (which powers my other radios fine), and the fuse pops. It happens in RX in all modes. It seems like amperage is building up somewhere (amp meter on DC neg shows about 7-8 amps before it quits)
     
  5. Cobra999

    Cobra999 New Member

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    OK - checked both tabs to back panel - no short.
    JP 11 to back panel - no short and
    JP94/89 to back panel - no shorts so far..

    JP11 to 94/89 continuity good.
     
    #5 Cobra999, May 1, 2021
    Last edited: May 1, 2021
  6. Handy Andy

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

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    It may be too late, the Transistors - Q49 and/or Q47 - one or both may have shorted to ground - and possibly taking out Q54.

    If you test the parts that you retightened, you may find it is now shorted, one leg shorts to the other - into both test lead directions - veryfy by just reversing them - same thing - it's blown shorted...

    To save time at least in pulling the part, remove that part you found loose - and fixed, unsolder and remove.

    That part, that one may be your problem, either way it needs to be checked out of circuit to make sure.

    A loose tab, on one transistor - then powered up, can cause that transistor to blow and melt into a molten pellet - a dead short of melted metal.

    So- the one you tightened - remove that transistor - unsolder it from the board and remove it, then power up the radio - see if stays powered up.

    • You won't be able to TX, but that doesn't matter - you couldn't even get it to stay powered up...

    Then if that doesn't blow the fuse, the part in your hand, is partially, if only hopefully is the truly bad part.

    Why do I say Partially? Because in moments of dead shorts, not just the part causing the short, but the CHAIN of parts to the short, are usually failing or ready to quit on you when you fix the original problem.

    There's a Murphy's Law in there somewhere...
     
    Shadetree Mechanic likes this.
  7. Cobra999

    Cobra999 New Member

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    Thanks Andy - I will pull it off this evening and report back! Chasing the rain clouds vs lawn mowing at the moment.
     
  8. Cobra999

    Cobra999 New Member

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    Andy,

    I removed Q49 as you suggested and the radio now powers on and RXs fine and is normal. I guess I need to find me a IRF520 IR704P.. Do you recommend a like for like replacement or should I upgrade the finals since I am already into it??
     
  9. Eldorado828

    Eldorado828 8-2-8 in the Lonestar State

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    Go back with what's there is what I would suggest. You could go the 13n10 route but there's no need to as the end result would be very close.

    Ranger uses the Vishay irf520 from the factory.
     
    Shadetree Mechanic likes this.
  10. Handy Andy

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

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    @Eldorado828 - and - @Cobra999 - that makes two of us!

    Yes, keep with Similar designs - locate the "symbol" or the Trademark of the part - Vishay, Infineon or even Rochester, locate the maker of that part and buy it thru a distributor like Digikey or Mouser even RF parts.

    The idea here is to keep the strip (TX strip) consistent - not all makers make this part EXACTLY due to infringements - so their performance should be within the ballpark - but not exact - just be consistent.

    Same brand doesn't a matched pair make, but the tuning and your expectations will give you better results - that being, having your radio back in operation.

    Buy more than just one - you may need it.

    And yes, tune for Current draw at the Test point - not set voltage - why? Minor variances within each part of the lot it will in the turn, affect the turn-on rate. Which will make setting by voltages a mistake, Please save your radio and you, those hassles, set by current draw to find the "exact" threshold moment of turn on.
     
    Shadetree Mechanic and Woody-202 like this.
  11. Cobra999

    Cobra999 New Member

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    Thanks and great advice Andy. I did get a 10 pack of IRF520s, purposely avoided anything that said IRF520N just to be consistent but I don’t know the manufacture of them - guess ill see when they get here. Do you suggest I just replace both at same time or do you think that’s not worth the time?
     
  12. Handy Andy

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

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    Do one, check the performance - try to keep the costs and your down time - down - for now,

    You have spares and thanks for noticing something I forgot to mention earlier...

    There are MAJOR performance differences between the standard IRF520, IRF520N and IRF520L

    The N and L suffix are Pb (Lead) free (PBF) and also have much different ON-Off states and voltage needs.
     
    Shadetree Mechanic likes this.
  13. Cobra999

    Cobra999 New Member

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    Unfortunately I replaced it and it did turn on and work a bit but no real power on meter and then appears that the 520 in q49 shorted out again.

    Where should I look next? Should I replace both the driver and final at same time? I don’t know enough about schematics to tell what could be happening
     
    #13 Cobra999, May 6, 2021
    Last edited: May 7, 2021
  14. Handy Andy

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

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    Hmmm, when you remove Q49 -

    Go to this link -

    http://www.cbtricks.com/radios/galaxy/dx959/index.htm

    Fid this section
    upload_2021-5-6_20-57-29.png
    Go, click on Main PCB ...

    You'll see this...
    upload_2021-5-6_20-58-51.png

    See Diagrams?

    It's the radios parts layout - look over the Graphic, and see both the TOP side and FOIL (Copper) side of views, VERIFY you're putting the parts where they belong - not shorting to rear panel - TAB of the TO-220 part can't short out to rear panel...

    From the component side,
    it should look like similar to this
    DUAL FINAL version
    Q49 is on the LEFT (Driver)
    upload_2021-5-6_21-3-58.png

    Note the assembly, the TO-220 tab is sandwiched - screws thru a washer spacer - and a spacer on the back of the part - use the white Heat sink goo, not silver or grey color - has to be made for RF - and insulated the part from the rear panel.

    From the Copper FOIL side, it should look something like this...

    upload_2021-5-6_21-7-33.png
    Notice the flowed soldering - no shorts and keep clean.
     
    NZ8N and Eldorado828 like this.
  15. Cobra999

    Cobra999 New Member

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    It def was not shorting out, but I didn’t add any white goo (which I do have) so I will put another in and make sure both sides of the white insulator are goo’d. Fingers crossed
     

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