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Uniden 68 and Cobra 25 not the same thing. What is this little pcb.?

Discussion in 'General CB Services Discussion' started by LeapFrog, Apr 28, 2016.

  1. LeapFrog

    LeapFrog Sr. Member

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    Hello Everyone, I have a question for somebody who knows these radios inside & out:
    cobra 25 ltd classic and uniden pc68xl.
    Everyone says the mods are the same, that's great ( although not my concern ).

    My problem is:
    I have a pc68xl and I ripped all the switches and potentiometers out to use in a Cobra 25, i had lost all the photos I took before removing the parts, now that im going to replace the parts i have no clue where all the wires go..

    Everywhere I look everyone seems to say and think that they are the same radio, clearly similar but they have some differences, just look at how the traces are a totally different style...
    The uniden pc68xl has a little board near the microphone input jack, this board does not exist on the cobra 25, what is it's purpose?..



    If I order Sam's Photofact # cb-207 am I going to find any information to help put this radio back together..
    If they were truly the same radio I could use a cobra 25 schematic, but they are not..

    http://www.cbtricks.com/members/toban/layout/25all.gif
    I found this schematic,
    if I pay for the samsphotofact (I've never seen one before ).
    Will i get anymore information than whats on this image?
    On the board there are no indication what the wires go to (no labels only color codes).
    The schematic has no color codes listed and it confuses me why are 5 wires used for ch9 switch and five wires for bright/dim switch is that really how many wires are used or am i reading it wrong, also no wires for the volume potentiometer, I can't find them on that schematic anyway.. Any help would be greatly appreciated, 73's
     

  2. LeapFrog

    LeapFrog Sr. Member

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    I am really not trying to buy another 68xl just to see how this one ($35 Radio) is wired up.

    I am gonna buy the SamsPhotoFact & I might just look for a Parts-Rig to Study and See how it's Wired Up, I Am Having Crap For Luck Understanding How The Wires Go From The Board To The Switches & Pots Using This Damn Schematic I Found..

    So if anybody has any advice they would like to chime in, then cool, otherwise I am gonna delete this thread.
     
  3. loosecannon

    loosecannon Sr. Member

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    first, don't use that schematic. not sure what that is, but its not the same as a PC68XL, or a cobra 25ltd.

    next, which version of the cobra 25LTD do you have? look at the audio chip and post back here which audio chip you have. that way we will know which schematic to use.

    the next step is to start with one switch or pot at a time.
    I can probably help you get them soldered in the right place, but i don't want to sit here looking at schematics that long in one sitting.

    so, tell me which 25LTD you are building, and which pot/ switch you want to start with, and we can go from there.
    SAMS CB 207 can't hurt to have.
    LC
     
    LeapFrog likes this.
  4. LeapFrog

    LeapFrog Sr. Member

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    Thanks Loosecannon I haven't been online in a while, the cohra 25 currently has a kia7217 from a 19wx. the original is a toshiha 7222 its a 1990 ltd classic philly, the original toshiba is good so im putting it back in the radio. I appreciate the help on this one. I have a uniden pc68xl philly newer than the cobra, unfortunately ive ripped the pots and switches from both units on a bad night. The uniden chip needs to be removed to see the numbers as its all black from what i see.

    I'll report back with a number once I pull it.
     
  5. loosecannon

    loosecannon Sr. Member

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    yeah they put those audio chips in backwards.

    when you post back, let me know which switch or pot you want to start with, and i will trace the wires on it.
    I will be working with the schematic so i won't be able to give you wire colors.
    you will have to find the part on the PC board that i reference, and then find the wire that connects to that part.

    i would like to know if there are any wires or wire pieces still attached to the switches and pots, or if you unsoldered all the wiring from them. that way i will know if i have to give you a diagram for the switches.

    also, you will need to do a test for me on the switches, as some of them connect the center contacts to the upper contacts when the switch is up, and some connect the center contacts to the bottom contacts when the switch is up.

    ill need you to tell me which type you have.
    LC
     
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  6. LeapFrog

    LeapFrog Sr. Member

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    {Response}: No problem I can/will. Unfortunately I have removed all the wire pieces, I have a multi-meter so testing the switches will be no problem though.
    For starters I would just like to do the volume pot / power switch combo

    The mic gain & squelch would be next.
    I previously soldered the RF gain wires together so it's already at the max position.

    And As far as the switches, I really just need the radio to not be stuck on channel 9 or in P.A. mode.
    Of course eventually I would like to put everything back to it's original state with all the switches functional, I know beggars cannot be choosers so I must say, Thank You Once Again!

    -Leapfrog
     
  7. loosecannon

    loosecannon Sr. Member

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    so i found a few diagrams that i think will help you out.
    I will still answer any questions that come up, but i think this will get you started at least.

    try this: http://www.cbtricks.com/radios/cobra/25ltd/graphics/cobra_25ltd_wiring.pdf

    here is a schematic just to use as a reference:
    http://www.cbtricks.com/radios/cobra/25ltd/graphics/cobra_25ltd_sch.pdf

    let me know what roadblocks you hit along the way and i will try to sort them out.

    remember that just because the diagram has wire colors on it doesnt mean that cobra used that color in all radios, so you will have to trace the wires back to the board to make sure that you have the right one.

    also, wanted to answer a couple questions you had earlier. first, yes the SAMS book will have lots of info in it that you will want to have. best source on cb radios around.

    as for the mic jack PC board, if one radio doesn't have one and the other does, you can be pretty sure that the components that are on that small PC board are on the main pc board in the other radio.
    LC
     
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  8. LeapFrog

    LeapFrog Sr. Member

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    Thanks LC, I'm making some coffee and will get at it today.
    The Cobra 25 is in worse condition than the Uniden, I may buy the SAMs book that covers them, info is pretty darn scarce online for the Unidens, I found a Polish Radio forum with a partial schematic for the pc68xl posted. I will post a link to that thread (if it's not against forum rules here) as it may help someone in the future. Also there is a nice photo of the underside with some wire to the switches partially visible.

    Thanks again, I'll be at it soon, hopefuly getting the solder iron warmed up. :)
    That wiring schematic is amazing, I don't know how I missed that combing over cbtricks.. Dang-Nab-It
     
    #8 LeapFrog, May 8, 2016
    Last edited: May 8, 2016
  9. loosecannon

    loosecannon Sr. Member

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    i just want to make sure i know what you are wanting to do.

    you want to use the controls from a PC68XL and put them in a 25LTD right?

    or is it the other way around?

    sorry for the confusion here.
    LC
     
  10. LeapFrog

    LeapFrog Sr. Member

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    I wanted to put the controls back into the uniden, I got the cobra for free and it needed pots, so one nit i ripped everything out of the uniden switched included and transplanted them into the cobra. When another problem was noticed with the cobra I decided I wanted go back to the uniden, and ALL the photos I took are lost (computer hardrive failed).

    I had given up on the cobra, and wanted the uniden back functional, because the uniden has no issues what so ever.

    When I saw your schematic posted I when nose first and decided on trying again on the cobra, so far I have the volume and power wires and mike gain figured out.
    Many wires were not on the schematic for instance w24 w25 were not filled with wire like on the schematic so i added them into the board..
    The channel display does not light up..
    The radio wil not go into transmit mode, I put the toshiba 7222 audio ic back in.
    It works in PA mode.
    What weird is the bright/dim switch is puttung it into PA mode or CB mode.

    The radio is recieving but the led will not turn red and it wont tx yet.

    Im tired of feeling like a pure failure working in this almost thirty year old cobra.
    My original intent was to get the uniden back together, at this point in the game if I cannot get the cobra to tx I will go back to the uniden...
    One day when I have enough pots and switches for both radios I will put them both back together for now im banging my just tryng to get something together for mobile..

    Thanks LC, -Leap
     
    #10 LeapFrog, May 8, 2016
    Last edited: May 8, 2016
  11. loosecannon

    loosecannon Sr. Member

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    ok, so we are working on the 25LTD with the TA7222 audio chip in it.

    we will start with the volume/squelch/power switch.

    picture this pot as two pots together that each have three legs on them, that also has two legs on it that go to a switch.
    so, two three leg sections, and one two leg section.
    if you hold the pot in your hand with the terminals facing you, and the turning shaft to your left, we can label the three sections as "front pot" (furthest to the left and closest to the shaft), "middle pot" (in the middle), and "power switch" (furthest to the right)

    we will start with the two legs that make up the "power switch".

    on the main PC board, find C124 on the main PC board. it is near T2. here you should find a wire attached to one side of C124 that also connects to T2.
    solder this wire to one of the two "power switch" terminals on the pot.

    now find C65, which is the main filter capacitor. you should find a wire connected to the positive side of C65. solder this wire to the other "power switch" terminal.


    now, we are going to do the squelch control which will be the "front pot" terminals referenced earlier. let's use the wiring diagram to make this easier.
    find the wire labeled W12 and follow it to it's terminal on the "front pot". we will call this 'terminal W12'.
    now find C145. it's near the front middle of the PC board. there will be a wire connected to one side of C145, and this wire should connect to terminal W12.

    next will be terminal W11 which is the middle leg of the "front pot".
    find C38. it's near VR4. find the wire attached to C38 and connect it to terminal W11 on the front pot.

    now for the volume portion of this pot, we are calling the "middle pot".
    in the wiring diagram, find the wire labeled W701. trace it back to the terminal on the "middle pot" and we will call this "terminal W701".

    Find C54 near TR10 and the audio chip. find the wire that connects to one side of C54 and connect it to terminal W701.

    have to stop here for the night. will continue tomorrow.
    feel free to work ahead if you see where i am going.
    LC
     
  12. LeapFrog

    LeapFrog Sr. Member

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    1990 Cobra LTD Classic with TA7222, does this check out so far?
    Still need the squelch and I am having issues with the switches as well.


    Thank You
     
    #12 LeapFrog, May 9, 2016
    Last edited: May 9, 2016
  13. LeapFrog

    LeapFrog Sr. Member

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    Here is a little shot of the 04/90 Cobra 25 LTD Classic board. I am a little surprised that the uniden is the same, it goes to figure that the little pcb in the uniden is just a relocation of some portion that is put directly on the pc board in the Cobras.

    A little update, I bought another pc68xl, I contacted Uniden and they will not/do not supply schematics or factory service manuels for their radios. (lol they want me to send it in)
    In the previous post (image)
    you can see what I have done so far on the potentiometers

    When I get the pc68xl in about a week, I will post a detailed wiring schema under the schematics forum. This will include the value of the pots, and wire locations. And switch wiring details.
    That way if down the road someone has a similar situation and needs a resource one will be available.

    I'm still sorting out the cobra, may pick up one of those as well because the switches are giving me hell, Loosecannon thank very much sir. I havent given up this radio yet. The schematic you posted is great, it just seems like it's newer because my pc board is more of a square shape towards the front and I have found no markings like wj701 so It's close, maybe close enough for my needs with just a little more guidance.
     
    #13 LeapFrog, May 9, 2016
    Last edited: May 10, 2016
  14. loosecannon

    loosecannon Sr. Member

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    well i know you can understand your notes, but they didn't make a lot of sense to me, so i will just continue here so that no matter what, you will have a place to go to get them wired right.

    I FORGOT SOMETHING LAST NIGHT!!!

    i forgot to tell you that the last terminal on the "front pot" goes to PC board ground.
    you will find a wire (probably black) going to PC board ground near the front of the main pc board on the side where the volume/squelch pot mounts. solder this wire to the last terminal on the "front pot".

    an easy way to determine if you have a wire that is actually going to PC board ground, just use your multimeter on the ohms setting, and put one lead on any of the tuning can metal shields, and the other lead to the wire. you should read a dead short.

    now we will continue where we left off.
    we have one terminal of the "middle pot" done, now we need to do the middle terminal of the middle pot. we will call this terminal W9.
    on the main PC board find R15. it will be somewhere near the L7 tuning can.
    find the wire attached to one side of R15 and solder it to the middle terminal of the middle pot.

    the remaining terminal on the middle pot goes to PC board ground, so use the same method i mentioned above to find another ground wire that will reach to the pot.


    sorry for not getting further with this. i haven't had a lot of time this week.
    I won't be on here for the next couple of days, but will get back to you with more info by thursday.
    LC
     
  15. LeapFrog

    LeapFrog Sr. Member

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    Thank You, so I can use any ground, the "BUS" on the schematic is not a straight ground plane attachment though.? I could test for continuity from the negative terminal at the back and it should be the same throughout the cans and ground wires.

    I understand life must go on, i'm glad your helping me I can wait if I need to.
    Thanks LC -Leap
     
    #15 LeapFrog, May 10, 2016
    Last edited: May 10, 2016

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