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Connex 3300hp almost dead

Discussion in 'General CB Services Discussion' started by Mk121, Apr 18, 2019.

  1. OldTech03

    OldTech03 Sr. Member

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    You must be able to think in more than one dimension there are open circuits and there are shorted circuits. If there is a voltage one place it doesn't follow that there will be voltage at the next place just because the schematic says so. There is a lot of real estate between TR41 and TR36 and a good bit of infrastructure in the sense of circuit trace.


     

  2. Mk121

    Mk121 Active Member

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    Ok everyone it's fixed. Oldtech you were right on the money! D77 was the culprit. It's replaced and it's working beautifully. A big thank you for helping me figure this out, I owe ya. Thanks to everyone else that helped as well.
     
    loosecannon and TM86 like this.
  3. loosecannon

    loosecannon Sr. Member

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    im not sure i understand what you mean OT03.

    if i measure 8 volts on the collector of TR41 with it connected to the PC board, then i am going to read 8 volts along that whole trace, no matter where i measure it.
    what am i missing here?
    LC
     
  4. Handy Andy

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

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    I came late to this party - been having a busy time with house and home stuff...

    But...
    3300VotlageRegulator.jpg

    IT would be easier to have said, check for 8 volts, then look at Pin 8, 7 and 7 of IC4 to see why it wouldn't toggle...

    But the big clue would be; to have checked for 8V and that would have brought up the display.
     
  5. Eldorado828

    Eldorado828 From the high plains of Texas

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    Better late than never Andy. Glad to see you back, haven't seen you chiming in for a little while now. Hope everything is A-ok
     
  6. Handy Andy

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

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    Thanks! Been busy here...
    Now why did I put seven and seven in there?

    SevenandSeven.jpg

    Well, maybe it was to wish you all a happy Easter!​


    But the issue around the D77 would have kept the Audio line high, forced muting of the chip - but also to pass along that many of these 4558 chips have ESD protection on their pins.

    I've seen several "confessed volted-up" boards that have had IC4 as well as other chips in various conditions of "Altered States" where the chip tries to toggle the 7 pin when you key up and pull low pin 5 when you key the mic. This can throw you for a loop if you're not researching it right.

    This reminds me of why GEICO is what it is...
    Altered States.jpg

    You also need to look at Pin 8 - it is the "source" pin for all the chips power - it uses the 100 ohm and the Diode - but if the chip falls it will try to sink or power thru current thru the output Pin 7 and if the ESD did it's job, and because of the volted-up condition that caused this - Pin 8 can drop like a rock or run at 1/2 supply rail simply because the output of Pin 7 is sinking into the Zener on TR36 / TR37 toggle combo...as in...ALL the supply rail. Meaning that the TX/RX/Power-Good check bank of pins on the chip is shot.

    So just a hint in case all else seems to fail - check for "Volted up" caps being blown - then you may need to replace several chips on the board - and make a call to the customer for the approval of the extra $$$ you have to now do to it...
     

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