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Ss3900 no tx on am and fm

Discussion in 'General CB Services Discussion' started by NODENS, Jan 12, 2019.

  1. NODENS

    NODENS New Member

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    Hi mates I buyed (as hobby) another cheap ss3900 with a funny behaviour (I love those one).
    It has tx on lsb and USB but no in am or fm. So all the path from mixer (ic9) until final transistor seems is OK. I checked the carrier oscillator (tr30) around and the coil l26 was open). Nice I thought that's an easy fix. I changed it and. Now I have around 5.6 volts in d57 cathod (the path for am/fm transmission for carrier oscillator (previously I had 0 volts).
    But yet not tx in am or fm (no swing at all or RF signal in transistors from ic9 ahead) .



    I have to say too that radio receives OK in all bands.

    Any idea what else could I check? I think something wrong yet around carrier oscillator (tr30).

    Thx very much
     

  2. jon666

    jon666 Sr. Member

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    did you check voltage regulator
     
  3. NODENS

    NODENS New Member

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    Do you mean tr41? It's OK providing the required volts. I believe something wrong yet on carrier oscillator area in am/fm tx related path
     
  4. jon666

    jon666 Sr. Member

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    i think its tr51 am regulator
     
  5. NODENS

    NODENS New Member

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    Ahh OK it's fine too, was tested and voltages OK and checked all final stage too. I think that problem is carrier related as l26 was open, one of the 2 frecuency path for tx needed. Voltages in all final stage is OK but no RF signal at all in fm or am only. USB, lsb OK and receive OK in all bands
     
  6. W2EKG

    W2EKG 201 Mike Action

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    Don't do this.
     
  7. NODENS

    NODENS New Member

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    Lol OK I will try
     
  8. jon666

    jon666 Sr. Member

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    oh no not again
     
  9. Handy Andy

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

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    OK SS3900 ...

    Start at #41 towards the top of the board. Check it for 8 volts.

    You obviously have USB and LSB meaning those sections are working but when carrier stops, you'll need to check the routing and ability of the MODE switch to send current (power) to the AM and FM section.

    That line is on J103 Header pin number 34, 35 and 38 - those are your AM and FM modes.

    IN FM #35 is the one that gets power, in AM #34 - so if that switch cant send power or the ROUTE from the switch thru those steering diodes D31 and D32 (part of where the Mic Amp audio goes to varactor to "wiggle it" with audio for deviation - check to make sure power is going thru.

    You already fixed L26, but did you check for power routing of that IF section? IF there was enough power to blow open a coil- then more that likely enough power went thru a diode to blow it open..

    Some diodes to check are 34, 35 and 36 along with entire set up to 40 all in that 2 X 3 row of coil area.
     
  10. NODENS

    NODENS New Member

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    OK Andy I. Will look for those sections you. Comment. The l26 indeed was open for corrosion below it, one leg was.....
    I had no counter or oscilloscope in that moment to see if 10.695 mhz was being delivered after coil replacement. Only Could to check that the Diode after the coil was being biased again.
    I will check your comments and try next weekend, I have to travel this week ). Thx for the input, I will continue next weekend.
    I know ss3900 is. Not the. Best. But at my area most of people or fishing ships have several of them and are easy to obtain and cheap. And a good hobby trying to repair them, is funny.
     
  11. Handy Andy

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

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    Hey good to know that you're able to keep it.

    As for corrosion, - you mentioned fishing - like open waters, and that too, may indicate there may be salt-water or even fresh water, corrosion issues in other areas of that board. They're not built for boating - but if protected from salt spray and or foggy mornings - they would last just as long and any other radio - aside from sinking with the ship...

    This opens up possibilities that even tuning caps may have failed due to moisture - you may have some work on your hands.
     
  12. NODENS

    NODENS New Member

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    The disc capacitor below l26 was dead as well, equipment working in all bands. It was funny to repair, I will give to someone hehehe and look another for next weekend. I have galaxy saturn 2, superstar 360fm, jopix alpha and a stalker vii in my radar for next funny weekend mornings)). Thx all specially Andy as always. I will finish understanding well this stuff hehe.
     

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