CB transceivers

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?

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* :-/ )

Have you tried to see if any of the receivers *actually* work ? You can do this easily enough by simply plugging an antenna in, and switching to a local channel of activity - CH19 would be a good place to start. Any old piece of random wire will do as a receive antenna, but do not attempt to use an untuned antenna as a transmit load. Most CB tranceivers are protected against damage from having a poor VSWR on the end of the transmit strip, but it may cause a PA shutdown, which then compounds your problem.

If you can find a working receiver, then there's a good chance that much of the low-level circuitry in that one, is working. Much of this circuitry is shared with the transmitter, so the VCO, PLL etc are likely - but by no means certainly - working correctly. If this is the case, then it's also likely that if it were placed close to another one with a working receiver, you would be able to hear it. Bear in mind that CBers are 'twiddle merchants', and the problems with these rigs may be little more than them requiring realignment.

You really need to get in there with a scope, and if available, a frequency counter. As a first move check that the VCO is running and locked on receive. Correct operation of the PLL / VCO is critical to both transmit and receive, and if its alignment has been twiddled, the radio will do neither ... Just as a matter of interest, do you have schematics ? Pretty much essential unless you are very familiar with a particular model.

Arfa

If in the USA and close to major roadways make a longwire antenna and listen for activity on ch 19. If you hear some activity try to transmit. Look at the tx indicator and any other that may indicate RF power. Some units could have broken mic cord connections. Some could have loose connections. Might be wise to make a 5 watt 50 ohm dummy load so you could try to transmit on one and listen on another and so forth.

Make TWO.

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.

--
Clint Sharp

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.)

In the time you spent on this e-mail, you could have brute-force tested all the units.

... 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! ;-)

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.

If I had to plan out a service strategy for everything I have worked on I'd still be back in 1990. Your advice should be heeded.

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.