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uniden washington 8719 channle mod question

Discussion in 'CB Radio Modifications' started by dss56, Jul 6, 2018.

  1. dss56

    dss56 Member

    Joined:
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    I have a washington where I think I add pin 9 to 14 8volts without isolating the pin 14. Now the channel 37 38 39 40 is 41 42 43 44 and will not go back to regular 37 thru 40. all other channels work. Did i pop the 8719 chip? I did change xtal to 11.3258. I totally forgot to isolate pin 14 with the 4.7k resistor.


     
  2. nomadradio

    nomadradio Analog Retentive

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    Hmmm.

    When you hooked the 8-Volt supply to pin 14, the channel selector would pull the 8 Volts to ground on the channels where that pin is "0". The selector simply switches the chip's pin to ground for a logic zero, and opens the circuit on that pin for a "1", with 8 Volts on that pin.

    Makes it sound as if maybe the contact point for pin 14 could have been damaged inside the channel selector?

    It's not that tough to check. Remove power from the radio. Put your meter's ground clip onto the radio's power-supply ground. Now set the meter to ohms, and touch the red probe tip to the channel-selector side of where you cut the trace to pin 14. Select channel 1. You should show close to zero ohms. Now select channel 2. The reading should rise to a few thousand ohms or more.

    If it does, the channel selector is okay. And if you can't get a continuity reading to ground on channels 2,3,4,8,9,10,11, 15,16,17,21,22,24,25,29 through 32, and 37 through 40, the switch is partly bad inside.

    73
     

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