I tried posting this over at a CB radio forum but it didnt work so ill post here:

I have a Realistic TRC-416 and while I was trying to hook it up to see if it worked(just got it out of storage) I think I corssed the wires. I put + to - and - to +(the power wires from the back of the cb were extended with the same color wire, that why i got them mixed up). Something inside started smoking. So Iopened up the cb and there was a piece floating around in their that looked like it had been burnt up. It wasnt attached to anything. I reall have no idea what it was. I called up my friend who is an electrician and he said I could try and solder it back into where it was and it migt work, the only problem is I dont know where it came from. I spend five minutes trying to find out where it fit but no luck. So, (1) can anyone tell me what I need to do to fix the cb and (2) does anyone know where I can get a wiring diagram for it for free?

Thanks
Joe

 

If you have no electronics background, throw it out and buy a new one. I just graduated college with an AAS in Electronics and computer engineering tech. and spent over two years learning just the theory of electronics in general and another 6 weeks working just on bugged CB's and it is hard telling what you burnt up. I would guess it be a couple of diodes used in the reverse polarity protection circuit, but who knows, could be a transistor or any other component that burnt open. By the time you buy a manual from Realistic, the parts or part if you are lucky, and pay a tech an hour or so to repair the damage...your looking at the price of a new $100 CB.

When you buy a new one, add a second fuse in line with the ground (-) wire and it will prevent this from happening again.

 

I'd either take it to a CB shop and they might be able to repair it, but it's probably a better idea to just get a new one.

 

well i went to a CB shop and the guy said it may be repairable. He said he would charge $35 to fix it and about $2 for parts if it could be fixed, if not, $10 just too look at it. I would have let him do it but i only had $10 bucks so i asked him what parts i needed and he wrote down a few part numbers and I went to radio shack. bought the two packages of diodes(he gave me two pns that said would work so i bought both). I opened up the CB and poked around and found where the diode most likely burned off from. I picked one of the two types of diodes and tries to solder it in. well at the time I could only find my big soldering gun so the solders were messy. I finished and hooked it up to see if it would work. no luck. i could have tried the other diode or flipped it around(i think they are directional) but I ran out of time. I think i may give it a try tomorrow but I think im just goin to get a new one. all i really want is the pa system. just fun to get on it and scare people.

 

PA systems are cool I want to hook one up to mine soon.

 

Yes...diodes are directional and only work one way. They have two ends, a cathode and an anode. The cathode is marked with a band (usually silver) around the diode. On a schematic, or the board if it is labeled, the anode is the flat end of the triangle and the cathode is the line across the point of the triangle. Hope this helps.

I think if i was in your situation, I would buy a new one. I just finished installing a Cobra that fit nice and neat into the overhead console of a 2002 Chevy 1500 p/u.

 

You took an electronics course and offered that solution?
You never fuse your ground line and if he did the same fault would have occured. If there was enough current to blow the fuse it would have blown the one on the pos line. Current in equals current out.

J15big, diodes are heat sensitive, you probably destroyed them soldering them in if you used a soldering gun. You need to use a soldering iron. 25 watts should be plenty. Also use heat sink clips (Radio shack) on the leads to protect them from thermal shock if you are not an experienced solderer. Heat the joint not the solder. Apply solder to the joint not the iron.
Diodes are directional and sometimes on the silk screen of the circuit board you will see a marking indicating where the cathode goes. The only way to be sure is to check the schematics. $35 bucks is not a bad deal. That is the average rate for one hour of labor in most shops. It is not an hours worth of work but in most shops that is the minimum charge.

 

thanks for the replys guys(hey that rhymes)
anyway, i think im goin to buy a new one later one. ill keep the one i have now and work on it if I have nothing better to do.

norm,
when i get the new one should i put the fuse on the ground wire or on the power wire?

 

Fuse on power wire ONLY!

 

ok, thats what i thought. thanks

 

Yes I have taken electronics courses and current in does not always equal current out...current gain??. The reason why I offered this tip was because I have seen it before on CB's, and no, fusing the ground lead is not a solution. The solution would be to carefully inspect/trace wires before applying voltage and to never assume. If a light fuse (1A or less) was installed, the second current started to flow in the wrong direction (wrong wire) the fuse would blow (on the ground side) before the one on the positive side. If the positive side was fused at say 15A, there is no way 15A of current would be able to travel through the circuitry , blow the 15A fuse, all before blowing a 1A or less fuse.

Please Norm, correct me if I am wrong.

Now, that I have thought about this, the best thing to do would be use a shunt diode with the anode to the - line and cathode to the + side (between the fuse and cb). This would work perfectly when wired properly. If the voltage was reversed, the diode would conduct and act as a short...blowing the positive lead fuse.

 

Yes there are gains and losses all through the circuitry but current into a circuit always equals current out.

Ohms law shows the relationship between Current, Voltage and resistance.
E=I*R.

E is fixed at ~ 12 volts in this case. In order to increase the current you must lower the resistance. Changing polarity will not do this.
If you take an ammeter and insert it in line you will get the same measurement on the pos lead as you would in the neg line.

Kirchhoff's Laws
Kirchoff's Current Law
The algebraic sum of currents entering and leaving any point in a circuit must equal zero.


Stated another way

No matter how many paths into and out of a single point all the current leaving that point must equal the current arriving at that point.


Kirchhoff's Voltage Law

The algebraic sum of the voltages around any closed path is zero.


Stated another way

The voltage drops around any closed loop must equal the applied voltages.



When voltages are opposing as seen at the right, the difference is the voltage applied to the circuit. In this case 4 volts must be dropped by the resistors to equal the applied voltage.

Therefore current in equals current out.

You are correct in saying that the solution would have been to be careful and inspect the wires before connecting them but hindsight is always 20/20 and J15Big has learned his lesson the hard way. I have been there myself, hands on is sometimes the best way to learn.
Fuses are not directional, there is no right or wrong way for current to flow in them. A 1 amp fuse would blow if the circuit drew more than 1 amp regardless of polarity.

 

Ah, Ohms and Kirchhoff's law, I am now remembering studying Thevanin's Circuits!

You are correct sir...current in equals current out. That is a given as you proved. I was just being wise, thinking about current amps and current gain. I see you have knowledge of electronics and I guess I was just kind of testing you. When you quoted me, I took it personally as an attack and felt insulted. I was at work when I responded very quickly to this post and I worked very hard for two years to graduate from school with honors. Thanks for correcting me on the brain cramp, I overlooked that the 1A fuse would indeed blow once the unit was turned on ( I knew fuses are not directional).

I guess the best thing to say to prevent this again would have been to install a shunt diode between the fuse and piece of equipment by connecting the anode to the - lead and cathode to the + lead. Everything would work fine until the voltage was reversed, the diode would conduct and act as a short, blowing the + lead fuse.

Come to thing of it, I have never fused the ground terminal of any equipment. I have been there also, but luckily was quick enough and lucky enough, the radio was not damaged (clip lead came loose and shorted the + to -).

_Matt

 

And for another $0.25, the factory could have designed-in a diode bridge (4 diodes) so that regardless of polarity, it wouldn't have let the smoke out.

 

you guys seem to know what your talking about but I dont. What is an anode and a cathode. What fuses shoild I get. 15A? Where should I put them? + and - ?
Please forgive the pic but I just whipped this up real quick on photoshop....is this right?