Disaster Planning and Troubleshooting Circuits
10/14/2009
Anyone who has ever participated in any form of Disaster Planning can relate to this blog entry.  How many of you have sat down with a group to discuss disaster planning, and found yourself saying “Hey, wait a minute!  This is getting ridiculous!”  The next thing you know the sky is falling, the sky is violet, the rain has created flooding that is 10 foot deep while the snow is 24 foot deep, and the temperature is over 150 degrees.”  Yep, that’s what disaster planning is all about - thinking about the unthinkable.  We’re going to focus on repairing CB radios in this blog, but you might enjoy reading about this type of planning in some of the stories told in “Apollo - The Race to the Moon” by Charles Murray and Catherine Bly Cox.  It’s a great book - written about the engineers and technical staff of Apollo.

Sometimes you have to resort to Disaster Planning (DP) in order to repair a radio.  When you have run out of ideas, it’s time to think about using DP. There are a few basic principles to using DP - a couple which are diametrically opposed to each other.  Huh? 

1.To use DP on a non-working radio, you need to understand how the circuit works.
2.Understanding how the circuit works makes it difficult to apply DP to the radio.

Hang in there with me for a minute or two. 

If you understand how the circuit works, you have the ability to look at each component with an eye towards “what would happen if component ‘x’ were to change value?”  That’s one of the basic principals of DP and troubleshooting.  The problem is that you start eliminating certain components or problems because you think “that can’t happen.”  You see, the more you understand the circuit, the more you tend to focus on “ideal components” that make up the circuit, rather than letting your mind run free with the “ridiculous” possibilities.  You weed out ideas because your understanding of theory tends to make you force logical, predictable actions from circuits and the components composing the circuit.  It worked at one time right?  So, the design cannot be so flawed that the circuit cannot work.  We also tend to think of components from a textbook application.  Caps are not supposed to have partial shorts of 100 ohms or so, etc. 

But to use DP on a broken circuit, you have to consider possibilities that seem absurd.  Would you think of the possibility that you might have a current leakage path due to contamination on your printed circuit board?  I’ll never forget a Cobra 29LTD “Philippines” radio that had terrible shot noise in both the receive and transmit audio.  The problem seemed to be all over the board (literally), and I could see the noise in my scope.  When I placed my scope probe on a totally isolated set of pads and read around 3 volts DC with a tremendous amount of noise showing on the trace, I finally took my trusty old RCA Senior Voltohmyst, placed it on the highest resistance scale and started measuring between isolated pads on the circuit board.  Imagine my surprise when I could measure as low as 300K ohms between a completely isolated group of pads (no connections to it whatsoever), and the adjacent pads on the board. Rosin Flux?  Some sort of chemical?  Let’s just say that I never found any chemical that could completely clean the board.  I noticed under a magnifying glass there was a faint outline of “silkscreen” showing up on the board.  I used an X-Acto knife, and “cut” a gap in the silkscreen between one of the isolated pads and the adjacent pads.  Low resistance readings gone!

The “art” of Disaster Planning requires plenty of practice.  The hardest part will be to stop dismissing some of your ideas as “impossible”, or “no way, that just can’t happen.”  And when you’re working at 27Mhz, seemingly normal components take on properties that are not always obvious.  So how do you get started?  Easy.  Even when the problem you’re working on seems obvious, think about what could be causing the problem by looking at the schematic and thinking about all of the possibilities it could be.

You’ll improve your understanding of circuit theory, but don’t let that get in the way of thinking some of the more “foolish” thoughts. 

You can always eliminate the “foolish” ideas by following through with some tests or measurements.  But if you don’t have some ideas as a starting point, you’ll never get off first base.

Before I jump out of here, let me leave you with a thought on another topic.

I see a lot of technicians struggle with no, or low power output problems on CB radios.  Let me give you something to think over.  Most of the time, the final and drivers are not bad.  I would say 95% of the time, the root of the problem is LOW DRIVE LEVEL.  I cannot count the number of times I’ve seen new finals, new drivers, even new pre-drivers installed, and the problem still remained.  The best way to troubleshoot low drive problems is with a scope.  You don’t need a fancy one - but it does need a Bandwidth of at least 40 or 50 Mhz to be usable for these kinds of problems.  You can pick up a good Tek 2215 for around $100.00 (less probes), or you can buy my all time favorite troubleshooting scope - the Sencore SC-61 for about the same amount of money.  Learn the various levels of RF drive found throughout the transmit stage, make notes on your schematics, and you’ll stop wasting time changing good parts out and start nailing the problems at their root the first time.  Until next time, send me your comments!  Rick

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Chess and Troubleshooting
10/07/2009
I will spend a lot of time blogging about troubleshooting over time.  But, chess and troubleshooting???  Well, chess is a game played between two people, so what's the connection?  If you look at a broken radio as your "opponent", you now have a game for two.  The best part about this game however, is that your opponent already has you in "check."  You don't start the game off with a clean board.  I've found that troubleshooting a broken radio is a wonderful mental excercise.  The great part about this game is you also get to move the "pieces" around looking for a solution.  Troubleshooting is a blur of science, skepticism, ingenuity, cunning, and sometimes a little luck  thrown in for good measure. 

There are many approaches to the troubleshooting process.  Entire books have been written about the subject.  One of my all time favorites is "Troubleshooting Analog Circuits" by Robert Pease.  Let me warn you though, you probably will never look at an electronic component the same ever again. You most certainly will find yourself saying "I didn't know it could do that!"

In this post, I'm going to briefly reflect (ponder, pontificate maybe ??, etc) on one of the world's great questions.

"I've never seen that before, what do I do now?"

Someone once ask me to share with them a tip or two about troubleshooting.  My first response was "Start by stopping."  Huh?  I cannot count (nor do I want to) the number of times I've been fooled into thinking I know what's wrong with a radio that's not working correctly
Most of the time it's my prior experience that's getting in the way.  "Now hold on a minute, are you saying prior experience has no place in the troubleshooting process?"  No, but I will say that relying on your prior experience as the first line of attack can cause you to waste a lot of time.  What we tend to do is try to make a problem "fit" a previous situation.  We'll spend more time attempting to put a square peg in a round hole than just starting fresh.

I keep a "sketch" or "outline" of most problems I've seen,  but I add something that really makes the difference for me.  I also add WHY the problem occured, and WHY the solution I applied worked.   I'll save my comments on the old saying "I understand how it works, but cannot really put it in writing" for another post. 
That WHY has taught me more about troubleshooting than just writing down "changed TR45" ever did.

There's another reason for being cautious about relying too heavily on previous problems and solutions.  You may have the beginning of a trend starting, and you're not really fixing the problem, you're just fixing the symptom.  I cannot count the number of times that I have been saved a return repair  by asking myself WHY the repair was successful.  I usually find myself digging a little deeper and finding the REAL problem in the first place.
Another "gottcha" comes from assuming that because you've found the problem and performed the solution that worked last time everything is now "swell."  You tend to not stand back and take another look at the radio and how's it's performing.  I just remembered another topic I want to talk about soon.  I'll call it "Alignments - for both the radio and your mind"

Next round maybe we can cover the art of "disaster planning and the art of troubleshooting."  Until next time, send me your comments.
Rick
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CB Radio Today
10/05/2009
From time to time I find myself wondering about the "state of CB radio."  Looking back just 5 short years ago CB radio has changed drastically.  Since I'm actually old enough to look back 10 years (and a whole lot more), I can say the CB of 10 years ago is all but gone.  You see, something strange has happend to CB radio.  If you say, "here's where he's going to trot out the word Internet", you'll be right.  5 or 10 years ago, CB radio users actually TALKED on their radios.  Yes, for those of you reading this post under the age of 25, that probably comes as a great surprise.  You would actually  hear conversations, gossip, cursing, kissing, dead carriers - you name it, but you actually HEARD something on some of the channels.  Today, you hear very little, yet CB doesn't appear to be "DEAD."  CB radio has become what ham radio and hi-fi was back in the 60's.  You see, people are buying radios with the express purpose of modifying and tinkering with them - THEMSELVES!!!!  Yes, you read right, they are actually buying their own soldering irons, meters, tools, etc and daring to take the covers off a brand new radio.  Years ago, the local CB shop not only would sell you the radio, they would perform all of the work on it.  Want an echo board?  No problem.  $80.00 got you a board installed in your radio.  Uh, excuse me, did he just use the word "install?"  Very few Cb'ers 5 years ago would dream of installing their own echo board.  Today a Cb'er willl shop for an echo board on-line, read the reviews, ask a bunch of questions, order the board, jump over to YouTube and watch a video of how to install it, pausing where necessary, and then jump onto one of the many CB forums for help when the thing doesn't work correctly.  WORKING ON and MODIFYING CB radios is what CB users of today do with their radios .  One Cb'er put it best..... He was trying to find mods for an early 80's CB radio.  He listed a few of the things he wanted to do.  Another user posted "you could buy a brand new radio with all of that installed cheaper than it would cost you to have all of that work done."  His reply?  "I know, I'm going to do the work myself, and the real fun is mod'ing my radio and then trying my mods out."  Let's look at it from another perspective.  For years performance enthusiasts have spent hours working on cars, motocycles, boats, ATV's, etc.  Put into perspective, messing around with some $5.00 garage sale CB radio for the fun of it is a pretty cheap hobby.  I know, I know, you'll point out those folks with 3CX10,000A AC boxes in the back of their vehicles, etc., but you have the local track for the hobby/weekend racers, and you have NASCAR for the pros.  Same thing in CB, you have the local bowls, and then you have the "super Bowl." 

Chances are very good if you're on this website, you're a DIY as well.  Some of you may be looking for Browning history, etc., but I'd dare say most of you at least do a regular "PM" on your own.  More and more of you are doing the repair and restoration work as well.  (please - just watch out for high voltage - something these new "puny" radio's don't have!)

The state of CB radio certainly is changing.  You know, I think I like it.  Working on CB radios was always a fun hobby for me.... I'm glad others are discovering it's fun to work on radios as well.  And like me, many of these people get more enjoyment out of working on a radio than actually talking on it.  There is one small problem however.  If all Cb'ers ever do is work on their radios, who's going to give us a radio check after we've spent hours working on the radio???? Send me your comments, I'd love to hear from you!
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