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uniden pc 66 XL no power

Discussion in 'General CB Services Discussion' started by kaos513, May 12, 2018.

  1. kaos513

    kaos513 Well-Known Member

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    Recieved a uniden pc 66 XL for a new project i will start off by saying no power at all this is a new project thanks .


     

  2. OldTech03

    OldTech03 Active Member

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    Just trace the flow from the cord to the board! And bamm you will find the problem. Ok also check for it being hooked up wrong and along with that burned traces on the board and maybe a bad switch, those kinds of things.
     
    Robb likes this.
  3. kaos513

    kaos513 Well-Known Member

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    there is power but not to channel selector and front tx/rx light now
     
  4. kaos513

    kaos513 Well-Known Member

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    replaced power switch no power still
     
  5. kaos513

    kaos513 Well-Known Member

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    im thinking the pll is a goner
     
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  6. loosecannon

    loosecannon Sr. Member

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    check Q18
    LC
     
  7. kaos513

    kaos513 Well-Known Member

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    q18 reads good
     
  8. kaos513

    kaos513 Well-Known Member

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    i read the block diagram from the cobra 25 looks like the pll powers the front of the radio it might had gone bad
     
  9. Low_Boy

    Low_Boy Well-Known Member

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    bad voltage regulator. That radio has 2 or 3 of them.
     
  10. kaos513

    kaos513 Well-Known Member

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    do u know which ones are they? i dont seem to find them on cobra 25 diagram
     
  11. loosecannon

    loosecannon Sr. Member

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  12. Handy Andy

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

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    Try testing Pin 1 of PLL, get 5V?

    TP2 - should show close to 4 V on Channel 40

    But if you don't have Channels display, then there's A LOT MORE work ahead...

    CB/PA issues, Channel 9 - stuff like that

    Physical damages?

    There are several PC66's - does this one look like yours?
    PC66ComponentSideTopsm.jpg

    PC66FoilSidesm.jpg


    :+> Andy <+:
     
    #12 Handy Andy, May 13, 2018
    Last edited: May 13, 2018
  13. Handy Andy

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

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    When you get this message, here's some help for you to work your way around and see why you don't get power.

    Refer to below to help guide you...

    PC66PLLLables.jpg

    The LED display, if it's blank, it's a "Self contained" Common Anode one, with the BCD GROUNDING the right digit segments on the twin display. So may have a separate problem with the display - Check Q18 BRT/DIM, Q17 as the MAIN POWER REGULATOR and Q16 is the TX - also powers Mic Amp.

    ON BCD rotary, There's a wafer in there that Grounds pins logic low for Frequency select. Internally floated/pulled high...

    PLL gets it's power thru R84 a 47 ohm resistor - this whole section is powered thru this resistor and it's 5V Zener regulator - Locate VR2 R84 - should have 10~8 V on one side with 5V on the other.

    If you get 0 V on the PLL side - this resistor usually is the one that fails due to the size and wattage - it's the fusible link in all of this and HOPE like h*ll - when you replace this part - you get 5V back.

    There is a large Electrolytic here and D13 is your Zener. C104 is that big one circled in pic. C101, C102 and C103 are similar issues - C101 and C102 2.2uF 50V are smoothing filters for the Phase loop detect section - C103 "slows" down the timing error loop to allow the Varactor time to catch up - it just smooth's the gating output so the VCO loop follows changes.

    If R84 doesn't restore power - look for more caps, this radio is built back in the late 90's so re-cap may be needed.

    L15, WAX CAPPED coil - is the peaking for VARACTOR - use TP2 for this. Channel 40 should be between 3.5V to 4.2 V DC. L16 - it's the 17~16MHz output for 1st IF image 10.7 - with L16 to peak this out.

    X1 is the 10.240MHz out for the 2nd Half of IF and TX image - peak it using RX mode and L5.

    Pin 8 of the PLL provides the 455kHz Shift using Q16 as the TX switch High / Low RX 455kHz Offset.

    Pin 2 of the PLL is the 10.240 reference.

    L18 dual core can - is similar to Cobra 29 and PC76/78 series radios - used for Mixer blending to make 27MHz out. IC2 27MHz is out into L17 by IC2

    Let me know if any of this helps!
    Regards!
    :+> Andy <+:
     
  14. kaos513

    kaos513 Well-Known Member

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    No 5volts going into pin 1 of ic3
     
  15. kaos513

    kaos513 Well-Known Member

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    Here is what i found so far i use my multimeter i get negative reading on my voltmeter, could be short anywhere maybe?
     

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