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Uniden PC122XL odd one

Discussion in 'General CB Services Discussion' started by sunfireman, May 10, 2018.

  1. sunfireman

    sunfireman Member

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    I just got a uniden pc122xl.
    It will need work but right now AM and Lower Side band works but Upper Side has nothing I key the mic and no tx light or power output in to the dummy load. Will have to dig a little more into it. Always liked the pc122xl great radios.
    Any idea on were to look first?


     

  2. 9C1Driver

    9C1Driver Sr. Member

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    You might clean the mode selector switch and see if it's just dusty and not switching completely into USB mode.
     
  3. Robb

    Robb Yup

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    Power on mode switch.
     
    psycho likes this.
  4. Onelasttime

    Onelasttime Well-Known Member

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    They are great little radio's for what they where meant to do. People always want to compare them to Grant or Cobra 148 and they where never meant to compete with those. They are very compact and very stable and if you do not attempt to get more than about 3-4 watts carrier swinging to 12-15 watts they will last forever.

    The weak point on them is their control face. The control pots are part of the control board they are not easy to replace and service like the bigger radio's. You can not just replace them with off the shelf pots and they always wear out and leave you with a nice radio with crappy controls.

    I have often thought about building a big box radio like a Dak V with off the shelf pots and meters and a PC122 main board or TRC465 453 etc.....If one of mine get's bad enough. I figure I could even do an internal sweep tube amp or a solid state amp and internal power supply etc....

    The Pro 810 has the same board for the most part and on those, since a house is cleaner than a car the controls do ok but the displays go bad.

    I am not too sure anyone has evermade a better compact SSB CB radio. The Galaxys do not even come close in terms of SSB stability but they do have more punchy audio since they are not using transformer modulation but IC audio/modulation. That allows you to exceed the previous 3:1 and 4:1 carrier/modullated audio ratio.
     
  5. kaos513

    kaos513 Well-Known Member

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    i aquired one for 10 bucks cant wait to see how howmuch work it needs.
     
  6. Handy Andy

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

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    Greetings!

    I guess I came in late to this but here goes...

    First, glad to know that you have at least AM and LSB, more than likely they had used it considerably for that...however if USB is "dead" - the best advice is to make sure the mode switch does work.

    When other modes are ok, and one side failed. My experience has taught me to fix th simple stuff then onto more complex...

    There are comparable radios - try this link...
    http://www.cbtricks.com/radios/realistic/trc_465/index.htm

    First things first, if the mode selector is not at fault - are you checking Solder joints for cracks?

    What caused the failure - dropped or mishandled - extracted from a car wreck?

    Possible broken wiring?

    Broken wiring yes, the things got a ribbon cable from the front panel to the board.

    So see if the mode switch is at fault you can probe the ribbon cable on the main PCB for voltages..and find which set of wires in the ribbon are bad. IF not voltages a simple continuity check from the mode switch back or the ribbon itself can prove good or bad. The voltage thingy is easier for quick needle swing, good, then onto the next one...

    IF that test shows good, then more the likely the next culprit is the diode steering for power routing in the modes.

    This is where you need to re-check the modes that do work for they can show you some insight as to why one is working.

    Open the case, use board ground not case ground for your negative lead.

    Power up the radio go to AM mode, find the mirror (jumper board) assembly that cover -shorts - three clips, this is the jumper that from the AM regulator located by the power connector UNDERNEATH it. More than likely this is ok, but I need you to do a voltage check on the mirrors assembly AS IT IS -DONT REMOVE IT FOR NOW... place a dummy load on the rear antenna connector to prevent accidents...

    Take the + lead and check in AM mode the mirror assembly, what is your voltage - don't need to whistle or jump around just you DO NOT NEED TO key dead carrier into that dummy load.

    Reading?

    Do it again but this time in the other SSB modes...and YOU DO NOT NEED TO KEY...

    Reading?

    IF you get 4~5 Volts on AM you should - you say that mode works.

    In USB? get Power supply 12~13.8 or whatever you're using for power feed - will be present here...

    LSB - you should get the same thing...

    Ok, let's check our readings...

    AM - 5 Volts? Good ok move on...
    LSB - 12 Volts? Ok, ok move on...
    USB - 12 Volts? Ok, ok move on...

    The above test is for MODE and if one of the poles is healthy - and if readings are like the above is what YOU get, that test passes...

    IF YOU DONT - the MODE SWITCH may still be OK...!

    You may have a Diode blown instead - so it pays to understand which of the symptoms are actually there - the more tests we do, the better choices on where to go to fix the problem...

    Does the USB Mode make the TX light turn on? Yes, Ok, that test passes...

    DOES USB MODE even transmit anything? As a signal into another radio nearby but you just don't have a receive?

    Then we have isolated at least what can go wrong and what went wrong...

    Ok, scenario time...

    USB DOES NOT MAKE THE TX LIGHT WORK - means POWER FAILURE and PLL will not lock. Diode failed...or Cascaded failure of diode routing.

    USB DOES MAKE THE TX LIGHT UP - MEANS that one side of the mixing is gone so you just don't have conversion - so more than likely 1/2 the radio functions. Diode failed...

    But I'll stop here, report back what you find - when you can!

    Regards!
    :+> Andy <+:
     
  7. sunfireman

    sunfireman Member

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    Thanks Guys. I will check the switch out tonight and check back in. Andy big thank you.
     
  8. sonoma

    sonoma Sr. Member

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    Andy I had one do this to me a couple years back. when I would go to USB the speaker would pop when switched to the mode and the radio acted as if it was dead. it had a bad cap in line that was bad. it was the one before the tuning coil. forget which cap was bad. just some thing to get you to thinking. you about covered every thing else for him to check.
     
  9. Handy Andy

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

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    Thanks Sonoma,

    I've had these 122's that had their front panels burned up, but not where you'd think.

    They tried to get 8 volts to clarifier from the mode switch's 8v side only the did the wrong pole and POP, SIZZLE AND BANG it's toast....

    Even had one that popped SSB mode due to the current they put thru the mode switch because they (at least it looked that way) were trying to check BIAS and popped the traces, not the switch, the front panels copper foil traces - when they shorted Collector and Emitter on the back panel with something on the driver...you could see the "weld" and when pressed they admitted to trying to adjust bias without removing the jumper...

    A lot of times I'd settle with someone for being "right" with me on how it failed - I'd fix it for free if they'd only confess and allow someone to work with them. In some cases, they came back with more, for more stuff to buy - proves that you can get more "bees" to work with you using Honey than Vinegar!

    Thanks !
    Regards!
    :+> Andy <+:
     
    Shadetree Mechanic likes this.

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