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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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    Update: radio is back on and I can RX no issue, all working normally.. I can also TX but this radio is pulling 5-6amps on keying so my 2.5amp power supply trips.. I have a 15amp DC unit but afraid to use it without and fusing as its a 13.4v 15amp supply..



    5.6 amps on key seems high but I guess a peaked 959 can do that?.. my bearcat 980ssb is 1.8amps on key..
     
    #16 Cobra999, May 8, 2021
    Last edited: May 8, 2021

  2. Cobra999

    Cobra999 New Member

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    I am going say 5-6+ amps is extreme.. saw a DC amp test on YouTube and I guess this radio should pull closer to 2.8-3amps.. so going to say something is just not right.. too much power killing the driver.
     
  3. nomadradio

    nomadradio Analog Retentive

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    Somebody has set the final and/or driver gate-bias voltage by watching the wattmeter.

    Not the current meter.

    Hint: Turning those adjustments "higher" will show a little more power on the wattmeter. And cause a 100% to 200% overload current on the final and driver. Not a wise tradeoff.

    Have you read the procedure to set bias current for the driver and final?

    Needs to be turned back down to factory setting.

    Preferably before the radio blows the face off the final MOSFET.

    73
     
  4. Handy Andy

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

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    Diodes are possibly bad, blown shorted from some kind of failure.

    When MOSFET, they need to be ZENER types, 5.1 to 5.6V 1 watt rated.

    you also install them where the BAND is towards the Gate (to the left) - in Bipolar days, the Band was towards the Ground - Emitter side (to the right)

    Better check those Bias pots, They may have opened, forcing full 8V TX voltage - causing "Zener" effect - you should be able to adjust from a low as 0.7V to as high as 4,5V nothing more. That is adjust...not just check for them...if the diodes blew, they'd blow open usually from the Zener-ing they perform (crowbar latch on) until reset or they pop like a fuse...

    Check traces, see the post I sent earlier - make the work as clean as possible and check the Bias section. Else what did happen will keep happening until it's fixed.
     
  5. Cobra999

    Cobra999 New Member

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    I accidentally deleted my last post but I was coming back to say I did end up getting the voltages to set right. I don’t know what I was doing wrong originally.

    So driver and final voltages set 3.65 and 3.75 respectively. The amperage at power wires goes to 4 amps and climbs the longer I keep keyed on AM., If I go LSB, the amps FLY over 8 quickly and pops fuse and trashes driver. Good thing I have 7 more...


     
  6. Handy Andy

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

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    Back it down!
     
  7. Cobra999

    Cobra999 New Member

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    I did make sure traces and solder is clean, double checked between all legs and legs and chassis for shorts, all good.
     
  8. Handy Andy

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

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    When I had problems like that I used to set up a flashlight bulb for 12V or #194 - between the TP9 and TP 7 or 8 whichever was giving me problems - the light bulb saves the part from taking all the power - worked to keep the Bipolars from "latching and blowing up"
     
    #23 Handy Andy, May 8, 2021
    Last edited: May 8, 2021
    Shadetree Mechanic and NZ8N like this.
  9. Cobra999

    Cobra999 New Member

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    I am just at a loss where to go next. If my voltages for driver and final are to spec, then what might be causing amp draw on LSB to go nuts on TX?. What could cause the amperage to go up longer key is down on AM? On AM TX amp draw starts at around 2 but will climb .1 very slowly if keyed down for like 20 seconds or more. Maybe normal?

    On LSB it starts closer to 5amps and gos up faster and I start popping things
     
    #24 Cobra999, May 8, 2021
    Last edited: May 8, 2021
  10. Cobra999

    Cobra999 New Member

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    I noticed while measuring amp on another working SSB, and keyed I get maybe 1.7-2amps, and amperage fluxes 2-7 with mic modulation. In comparison on my 959, I can be completely silent, no mic gain, no RF power but amperage still shoots over 4-5 when on SSB RX. Just adding some more interesting things hoping this might help.
     
    #25 Cobra999, May 9, 2021
    Last edited: May 9, 2021
  11. Handy Andy

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

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    The LSB issue can be many things - sounds like some form of carrier is being sent thru - the Final and Driver may not be the biggest fault here, but you may be stumbling onto something that caused the original condition and to lose the Driver in the first place.

    Go back the start of this thread, and you came across what you thought was loose hardware - ok, now you fixed he Driver and it seems to work then abruptly you are still are losing the Driver (or Final) so it looks like you're fixing a symptom, but have yet to find the cure.
     
    Shadetree Mechanic likes this.
  12. Cobra999

    Cobra999 New Member

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    I was able to use AM fine, so I assume driver and final probably OK.
     

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