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CB transceivers

Discussion in 'Electronic Repair' started by William Sommerwerck, Dec 17, 2009.

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  1. Don't you have a working receiver you could first use to find which are
    transmitting?
     
  2. D Yuniskis

    D Yuniskis Guest

    I chuckled to myself as I pondered this problem -- it
    reminded me of similar math/logic problems as a kid
    that also seemed "unsolvable" (on the surface). So, I'm
    looking for a similar twist to solve this one...

    I have several rescued CB transceivers of indeterminate
    quality. Since I have no idea what portions (Tx vs Rx)
    of any of them work and which don't, how should I go about
    sorting those that are keepers from those that belong in
    the recycle bin?

    Obviously, the first pass is to try Tx on each and see if
    *any* of them receive. This tells me I have one good XMTR
    and one good RCVR. From that, I can deduce the status
    of all the other Tx and Rx.

    But, what if none of these combinations work? I would
    assume this would be bad Tx in all (as I would think it
    easier to fry the output stage than *all* of the receivers)

    Any other tricks I could try?
     
  3. D Yuniskis

    D Yuniskis Guest

    No, that's what makes it so similar to those math puzzles...
    how to get information without having any!

    (I think turn them all on and individually key them one
    at a time is the best place to start. If *none* of
    them appear to work then either they all have bad Tx or
    they all have bad Rx. In either case, they are all *bad*
    :-/ )
     
  4. GregS

    GregS Guest

    Make TWO.
     
  5. Clint Sharp

    Clint Sharp Guest

    Not that difficult in practice, if you have a failed TX PA stage (most
    likely) it will still produce enough signal to open up a working RX.
    Likely you can also watch the meter on the TX, with a bad PA it will
    still move up a little. If it drops to zero then it's likely that the
    VCO is out of lock. There is enough repair info on the web that you can
    solve most problems given enough patience and a little skill.
     
  6. D Yuniskis

    D Yuniskis Guest

    They are all handhelds so each has a telescopic whip antenna.
    However, we are quite far from any large highways so picking
    up any trucking traffic, for example, wouldn't be possible
    (it's a 30 minute drive to the nearest interstate highway)
    The problem is you need *two* working receivers. I.e., if the
    receiver on unit A works, the only way to test the transmitter
    on unit A is with a working "unit B" (?)
    All of the sets appear to be highly integrated. Digital PLLs,
    etc. I wanted a quick way to cull the "dead" from the "undead"
    and then decide if any were worth repairing. This isn't
    a hobby, etc. Rather, just deciding if any are worth tossing in
    my bugout bag or if they should all just go in the "trash".
    I won't start looking until I know which units are worth
    my attention. I think I have six different units here
    each of indeterminate quality... (I would like to get those
    that don't work and aren't worth my attention out of here
    to cut down on clutter, etc.)
     
  7. I won't start looking until I know which units are worth
    In the time you spent on this e-mail, you could have brute-force tested all
    the units.
     
  8. D Yuniskis

    D Yuniskis Guest

    .... and LEARNED absolutely *nothing*! Like, "Gee, do I have to
    screw this antenna on *before* keying the transmitter? After
    all, the receiving unit is just a foot away... why bother
    putting the antenna on?"

    How would that have helped me sort through the various HAM kit
    waiting to be tested after these??

    Perhaps I should just have discarded the whole assortment?

    I am touched by your apparent concern for how I spend my time! ;-)
     

  9. I can be rather blunt, Mr. Yuniskis.

    I've learned -- from my own experience, as well as others' -- that people
    often waste a huge amount of time planning to do something, instead of just
    jumping in and doing it. *

    In this case, planning would have had little effect. You should have hooked
    a suitable transmitting antenna to one unit, and a short wire to another,
    and seen what happened.

    The Amateur equipment is another matter. You have the SW bands to see
    whether the receiver works. Once you find a working receiver, you can
    proceed from there.

    * I've been servicing electornic equipment on and off for 50+ years. (In the
    past 20 years, more off than on.) There are two approaches to service --
    figuring out exactly what's wrong, or simply getting the item working again
    by any means. As an intellectual, my natural inclination is to the former --
    but you can waste huge amounts of time. More often, the "try anything"
    approach is more efficient.
     
  10. D Yuniskis

    D Yuniskis Guest

    Herein lies the difference! I've been designing equipment
    (medical devices, computer peripherals, gaming machines, etc.)
    for the past 30+ years. There, you learn that NOT planning
    (i.e., "jumping in and doing it") ends up wasting a LOT of
    time and usually leaves you chasing after a bad design strategy
    that you would have figured out had you only thought it through
    *before* starting. While a repair might require a few TENS
    of hours, a design may require a few THOUSAND hours. Hence
    the folly of not planning.

    I took your advice -- since there were no other hints that
    might have saved me appreciable time (though I now recall that
    one of my older PC's could have been used as a crude signal
    source to at least get a rough idea which receivers showed
    signs of life).

    Had I had 50 or 60 "batteries", this would have been much
    easier -- I could have installed batteries in each unit,
    set squelch to minimum and keyed one unit at a time
    while listening to see which, if any, of the other units
    received signal. As it was, I had to change the batteries
    after each test (I had enough batteries for one unit and
    an AC adapter that worked on only some of the units -- so
    I often had to switch the adapter to "the other unit"
    when testing certain pairs).

    I made a chart showing each (Tx, Rx) pair and the results of
    the first pass. From that, I was able to rule out two sets
    that didn't look like they would ever be worth pursuing.
    The others I ran through the same routine again -- this time
    borrowing some C-Zn cells so I could eliminate the battery
    eliminator (it seemed to cause 60 Hz noise on some of the
    units of an amplitude great enough to swamp the transmission).

    I *think* I now have four likely candidates to do extended tests
    with. I'll put them in the car for the next time I am close
    enough to the interstate to pick up some traffic there.

    It took me the better part of 2 hours to test each combination
    of tranceivers (6 units means 30 combinations -- actually,
    they are permutations as order is significant). Considerably
    longer than the time spent on these USENET posts... :-/

    In hindsight, "planning" would have had me purchase a bulk
    package of batteries at Costco and testing them en masse.
     
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