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Galaxy No am tx but ssb works fine

Discussion in 'CB and Export Equipment and Accessories' started by Northwoods, Feb 2, 2021.

  1. Northwoods

    Northwoods New Member

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    Hi all,
    New guy here, but have been around cb radio all my life. Hoping someone can help with this issue I'm having.
    I have a galaxy dx95t with the ept6900 board. It lost tx on am but ssb is still working. No voltage getting to collector of q54, meaning no voltage getting to driver or final. Tx light is switching. Just no carrier. My first thought was to replace q54 but no luck.
    Thanks in advance and I did try using the search function.


     
    #1 Northwoods, Feb 2, 2021
    Last edited: Feb 2, 2021
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  2. Handy Andy

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

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    upload_2021-2-2_10-11-58.png
     
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  3. Northwoods

    Northwoods New Member

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    No voltage on collector for q55. Voltage missing on q53 base and emitter. Q53 has correct collector voltage.
    Thanks
     
    #3 Northwoods, Feb 2, 2021
    Last edited: Feb 2, 2021
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  4. Handy Andy

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

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    IF VR14 is showing you can adjust power to Q53, but Q53 isn't sending power to the Darlington, (Q55 Q54) and you can Rule out NPC mods, Does SSB Power adjust with Front panel RF Power control?

    If control - locate C235, Q58 - the Q58 "mutes" the audio for FM - but if it's shorted or something is done to C235 to short it out - Q58 won't let Q53 send any current to Q55/Q54 pair.

    But then Don't rule out Q53 being the culprit. D108 and D107 act as a steering pair to the RF power control to allow the greater of two power levels - Envelope or AM/FM Power Trim (High) to route thru RF power knob.

    Verify FM works and you have power control on that mode too.

    Q56 is Envelope Control - check to make sure it's not adding to this problem. A quick adjust of VR17 can prove this parts ok.
     
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  5. Northwoods

    Northwoods New Member

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    I did already replace q53. Also voltage can not be adjusted with vr14 in am only in ssb at q53. Same with q56 and vr17, only able to adjust in ssb. Same with rf power knob.

    Just checked fm, it is dead as well. I'm going to find q58 and check it now.

    Thanks
     
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  6. Handy Andy

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

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    I'm on the hunt for it too...
    upload_2021-2-2_17-20-54.png
    There ya go...
    Long way to Tipperary by that route...
    Capacitor that can fail is right next to it.
    You can thank Bennie at CB Tricks for this...
     
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  7. Northwoods

    Northwoods New Member

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    Yep I got it swapped out..still nothing.
     
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  8. Handy Andy

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

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    AM PWR at least in light of the 8 volts, is run thru the Front Panel and a Rotary knob.

    At Q58 - was C235 shorted or somehow sucking out power from Vr14?
    upload_2021-2-2_17-54-50.png

    Header at J14 ok?

    upload_2021-2-2_18-0-43.png
    Just curious as if 8 volts even appears at VR14 in FM and AM modes? IT's direct from J14 - so if dead, check continuity. If Q58 is getting power at AM and FM mode, then suspect a wiring mishap.

    Q31 and Q30 handle the Red light TX on, so if it can pull current - you should get 8 Volts at VR14 to adjust.

    May also indicate a Dead/shorted Diode in the USB/LSB modes - that when in AM/FM mode, will not knock down (Turn off) Q58, or Q56 properly with the correct voltage - that is done thru the Diode matrix D84 thru D87 - any shorts there can cause this condition - thinking it's in SSB mode when it's not.
     
    #8 Handy Andy, Feb 2, 2021
    Last edited: Feb 2, 2021
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  9. Northwoods

    Northwoods New Member

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    I have 8 volts present at vr14 in am and fm with adjustability. Then after that it just seems to get lost.
    I can check out those d84 to d87 diodes.
    Thanks a lot.
     
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  10. Northwoods

    Northwoods New Member

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    Q58 is replaced but not getting power in either am or fm.
     
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  11. Handy Andy

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

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    Well, if you get a voltage at VR14, but not at Q53, it uses a resistor divider to apply that adjustable to the Base - and since you don't have a voltage at the Collector in AM, but you have VOTLAGE in SSB. Then Q55 or Q54 seem ok, then the toggle portion of this seems ok, but what turns on Q55 to full rail voltage when in SSB mode?

    Or, what is still left on when you switch from SSB back to AM or FM modes?

    PNP transistors are funky devices, they work opposite of NPN's...

    When Base goes high on NPN - they can turn on.

    The the Base goes high on a PNP - they turn off...

    So again, re-measure voltage at the Base of those PNP's if they are flat/High - switch to SSB then check again, if not flat - what voltage do they show?

    I just hope all this work, and you have a transistor in backwards throwing this all off....
     
    #11 Handy Andy, Feb 3, 2021
    Last edited: Feb 3, 2021
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  12. Northwoods

    Northwoods New Member

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    Q55
    Am b 13.6 ssb b 13.1
    C .3 c 9.5
    E 13.7. E 13.5
    Q54
    Am b 13.7 ssb b 13.5
    C .3. C 9.5
    E 14.1. C 14.1
    Hope that helps.
     
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  13. Handy Andy

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

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    Helps A lot...

    Go back to Q56, you may have a blown Cap (C242) or D108 is bad...at least it(they) could be shorted.

    check Q56 voltages when switching modes and see what is going on.
     
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  14. Northwoods

    Northwoods New Member

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    I also thought about c242, so it's already replaced along with c238 and c239.
    D108
    Am - Anode 0v / cathode 4.27v
    Ssb - anode 4.4v / cathode 3.9v

    Q56
    Ssb - E 3.8v c13.1 b 4.4
    Am - E 0v c13.7 b 0

    Thanks for your patience
     
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  15. Eldorado828

    Eldorado828 8-2-8 in the Lonestar State

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    You've got me reading attentively..... I'm hoping for a good outcome here!
     
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