Troubleshoot With Basic Theory

By

David R. Anderson, KA2FEA

Every electronic circuit is an entity that can be broken down into the components it contains, such as tubes, resistors, capacitors, and coils. The theory behind the operation of these components and their characteristics, as well as the theory behind operation of the circuits, is the basis of every course in electronics. It is no secret that a service technician, whether he is a beginner or a professional with many years of experience, can save a good deal of time and effort by applying this theory in his work.

Taken as a whole, a unit of electronic equipment is quite a complex affair. One of the first things an application of basic theory does is to allow the technician to simplify analysis and troubleshooting procedure by dividing the unit into individual sections or circuits. With theory, he can narrow things down even more, but this is less often done than the common technique of section division. However, before getting into theoretical analysis of specific component defects, a review of the initial sectioning off is worthwhile.

Each circuit may be considered an individual unit with an input and an output. In some cases, there may be more than one input or output. In other cases, such as the i.f. amplifier of a TV receiver, it is more convenient at first to consider the group of circuits (stages) contained therein as a single section.

Keeping to the TV receiver as an example, it may be divided into several portions, or blocks in a hypothetical block diagram, each of which has a particular function in either delivering a satisfactory picture to the screen or sound to the speaker. The tuner, i.f. amplifier, detector-video amplifier, sync amplifier-separator, horizontal-sweep high-voltage system, vertical-sweep system, audio section, and power supply would be included in a typical breakdown of sections.

There may be some interaction between sections with certain faults, but systematic checking will show this up. This procedure, of course, is not confined to TV sets. A division into functional sections is possible with test equipment, ham gear, hi-fi units, or any electronic equipment.

Even after this approach is followed until the fault is localized to a specific section, the possibilities of the technique have not been fully exhausted. Similar logical elimination can be applied to location of the specific fault.

Let us assume, to start, that we have a TV receiver in which there is no picture, although a full raster and sound are present. The technician reasons along these lines: since the sound must pass through the tuner, i.f. amplifiers (in an intercarrier receiver), and audio sections to reach the speaker, and sound is present, these sections are at least operating. Also since the circuits mentioned depend on the power supply, the latter must also be functioning. Since the intercarrier audio i.f. signal originates in the video detector, the latter is also operating.

Already a large portion of the receiver circuitry has been eliminated from primary suspicion. Other sections can also be set aside. Because a raster is present, the electron beam of the CRT is moving, and is being deflected across the screen both vertically and horizontally. Therefore, the sweep circuits are operating, as well as the picture tube's associated circuits. For example, the presence of the raster indicates that high voltage is being developed.

At this point, without using a single test instrument or making a single measurement, only the sync and video-amplifier sections remain open to suspicion. Since the complaint is that of no picture, it does not matter at this time whether the sync section is working or not. The technician is ready to concentrate his efforts on the video amplifier, and he is ready to bring his equipment into play.

Assume that the video amplifier in question is the single-tube, two-stage circuit of Fig. 1. The next step may vary depending on the technician's preference or the nature of the circuit. With a good oscilloscope or other equipment for observing the presence or absence of signal, the technician may resort to signal tracing for further localization before he undertakes voltage and resistance measurements. In a circuit that is reasonably uncluttered he may go directly to these measurements. In either case, he can reduce the number of tests required by logical use of theory.

This theory tells us that each component has its own normal effect on circuit action depending on how it is used; and also that it will have certain effects when it becomes defective. Thus in any circuit there will be a number of components that may be eliminated from suspicion because they could not cause the symptom for which the equipment is being serviced.

With reference to Fig. 1, components such as R5. and C3, would not be responsible for the symptom of no picture even if they were defective, because of the way they are used. They help determine frequency response of the video amplifier, but do not essentially couple signal or block d.c. If R5 shorts, the path from the V1a plate to the V1b, grid for d.c. and signal voltage already existed through L1, L2 and C3. If R5 becomes open, the alternate path just mentioned still exists. Similarly, a shorted or open C3 will not affect d.c. voltage or the signal path appreciably. Picture quality might be seriously affected, but the picture would not be lost altogether. Thus still without measurements - reason has removed two components from serious consideration. Similar reasoning eliminates L1 and L2, making the total four.

Assume that the first reading, al the plate of V1a, indicates noticeably low "B+" voltage here although a check shows that the power supply is operating normally. The schematic reveals eight components that still might be involved with this condition: V1a, R1, R2, R3, R4, R6, C1, and C2. But we can eliminate two of these from suspicion.

Low plate voltage may be present because R1, has increased in value or because the tube is drawing too much current. If the latter is true, then the grid is too positive or the cathode resistor is shorted. However the grid components, R2 and C1 do not seem to be involved. If R2 were open, the charge on C1, caused by grid-current flow, could not leak off. Thus, the negative voltage on the grid would increase, tube current would decrease, and plate voltage might rise somewhat, but would not drop. But what if R2 were shorted? We would still have the cathode bias resistor, R3, which would keep plate current down and plate voltage up. So much for R2.

As for C1, it would have little effect on the operating bias if it were open, so it would have little effect on plate voltage. Suppose that C1, is shorted or leaking. If this component was intended to block d.c., some positive voltage would now pass through it to affect operating bias of V1a and plate voltage would go down. However, there is no positive voltage available at the output of the detector to do this C1, may now join R2, as being exonerated.

With a single measurement and the application of theory, the defect has not only been narrowed down to a single stage, but six of the twelve possibly defective components in Fig. 1 have been set aside. The few minutes spent in studying the schematic to make these conclusions involve less time than it would lake to make checks on the several parts that are not likely to be involved.

Even with components that may be involved, it is not necessary to perform all checks on each. The various ways in which a component may become deflective, and the effect of these various abnormalities on the circuit, may also be taken into account. For example, resistors may become open, change in value, or possibly (though not usually) short. Capacitors may short, open, leak, or change capacitance. Coils may have shorted turns, which will change inductance, or they may develop an open winding. Tubes are subject to open filaments, shorted elements, open elements, and changes in characteristics.

Each type of defect for any given component will affect the circuit in which it is used in a specific way. Therefore, a suspected component need only be checked for the type of defect that could cause the complaint being serviced. For example, it would be un-necessary to disconnect one end of a capacitor for a leakage test if the symptom observed could not be caused by leakage. Conversely, with low plate voltage on V1a, of Fig. 1, C2 would be checked for leakage or shorting, but it would not be necessary to place this capacitor on a bridge to find out whether it had lost capacitance or was effectively open.

The samples chosen here illustrate the method but certainly do not exhaust all possibilities. In any event, they indicate that the systematic application of theoretical analysis does more than provide mental exercise. It can save much valuable time."

KN

This article first appeared in the October 1960 issue of Electronics World Magazine.

Special Event Communications

Public service through providing special event communications has become an important part of amateur radio. But providing communications is more than just grabbing an HT and heading out to the event. To do it well, there are a number of rules and procedures that should be followed. The following is part 1 of a 2 part series taken from a handbook prepared by the Santa Barbara Amateur Radio Club (SBARC).

"A Handbook for Amateur Radio Operators'' by Lou Dartanner, N6ZKJ.

What is "Event Communications”? SBARC works cooperatively with local non-profit organizations in their events by providing communications to insure the safety of all participants. Each event in which we participate has been reviewed for appropriateness by our Vice President of Operations. The event sponsor is required to provide insurance for the SBARC members participating. This insurance provision is the main reason why event communicators must be SBARC members. The FCC's interpretation of public service assistance that Amateur radio operators can render is keyed around safety issues, such as providing communications to notify event officials of medical emergencies or logistical requirements. But we are specifically prohibited from engaging in communications regarding the event itself, such as the number or name of the lead runner to release to the public. We can take no compensation for our participation in an event, but can accept T- shirts or meals provided to other helpers and/or participants.

Radio Equipment: Of course, you need a radio! A 2-meter HT will suffice, but there are some accessories for your HT you will really need if you will be doing event communications. The "rubber duck" that comes with your radio is OK under most conditions. You should have with you a 5/8 wave telescoping or a 1/2 wave "loaded" whip for areas with a marginal path to the repeater. Earphones are a must. An inexpensive set used for portable AM/FM radios is OK. It's best to have a set that covers

both ears and you can buy a mono to stereo adapter to put audio in both sides. A speaker mike or headset (combination of earphones and mike) is handy. Headphones can be plugged into your speaker mike. This enables you to take your radio off your belt and hold it in the air to get the antenna up for a better shot at the repeater in marginal areas.

A word of caution about speaker mikes. It’s tempting to clip your radio to your belt and hang your speaker mike over your shoulder, but remember your antenna is around your waist and you’re transmitting more signal to your kidneys than to the repeater!

Buy an alkaline battery pack and put in fresh batteries before the event and carry a spare set. Nicads are really unreliable; you never quite know their charging status and they fail at the most inopportune times. It's not easy to recharge Nicads in the middle of the triathlon! It's also handy to have a magnetic-mount antenna. If you are assigned to a SAG wagon or other vehicle you'll have an outside antenna for your HT. Also, if you're way out in the "boonies" you can put the mag-mount on your own vehicle and stand near your station and have much a much better signal to the repeater.

Personal Equipment: The next consideration is what you will take with you to make your job safe and comfortable. You can usually put your radio and personal supplies in a "fanny pack" or small backpack. Of course, wear comfortable clothing and shoes and bring a hat. It's best if you wear an SBARC Event Communicator or Club T-shirt to help identify your position. You should try, to be self-sufficient and not rely on anyone else. Some things to bring: water or juice, a snack, sunscreen, a few Band-Aids, hand wipes, and tissue. Also, bring a copy of your FCC license, a notepad and pen, a map, and your instruction sheet from the SBARC event organizer.

Working The Event: Before leaving home, be sure you have everything. Program primary and alternate frequencies in your radio. Select high power. Lock the keypad. (It's an awful feeling to hear "beep-hoop" and not know what your HT did so you can get it back to normal! Be sure to be on-station on time! This usually means allowing extra time to find a parking place and get things together. Check in to the net. Locate your assigned position or find your official and introduce yourself.

Your job is to "shadow" or stay beside that official and pass information to him or her as necessary. We do not provide communications for the public; you may be asked when the parade will start or where a particular runner is, but politely say you are not in a position to know and can't interrupt the net to find out. When your official wants to send traffic to another official, consider putting them on the radio as third-party traffic. Just identify after they are finished talking. Remember, your job is communications. We are not supposed to help the event personnel. You may miss an important message if you're out directing traffic or handing out water

Watch your background noise:

Parades are particularly difficult to work because the noise is very loud. This is why earphones are helpful; they allow you to be able to hear the net through all but the loudest band. Be aware of background noise when you transmit, too. If a train is going by or a band playing, you might have to say "stand by" and respond when the noise subsides. Don't try to talk over the noise; you'll only cause your signal to distort and you won't be understood anyway. If possible, use a noise cancelling microphone. Do NOT try to use a VOX (voice-actuated) attachment. A "stuck mike" can completely shut down event communications. Never put your radio's or headset's transmit switch where it can turn the transmitter on without your knowing it.

If you haven't heard anything from the net in a while, check your radio to make sure you're on receive and the right frequency. Check your instruction sheet for directions. You may also receive verbal instructions when you get in position, such as to notify Net Control when the first swimmer makes the transition to bicycle. Tactical call signs (Check Point Three, SAG Wagon, etc.) are perfectly legal. Just ID with your FCC call sign after a communication exchange is completed. You may also use the suffix of your call sign as a tactical call, signing off with your complete call. When working events, you should make the transition from your ham radio hobby to an Amateur radio avocation. It's fine to be chatty and laugh with the mike open in ham radio, but it is unprofessional when we're at work.

Good Operating Practices: Aim to project a professional image with proper operating practices, whether you're a net controller or a field unit. Keep traffic to a minimum. Say what you have to say then release the frequency. Silence is Golden -- it allows someone else to use the channel when he or she needs it.

Some things to remember to help you be an efficient, professional-sounding radio operator include: Pitch, tone, and volume of voice. A moderate tone and pitch are desirable. Too high a voice can be irritating, too Iow can be hard to decipher. While you can't go out and buy a new voice, you should deliberately lower your voice pitch slightly when using the radio unless you have an especially low voice. Try for an even modulation, but not a monotone. Don't trail your voice off at the end of your message--the last part is just as important as the first!

Speed. Too slow and your listener may try, to anticipate your next words or may not understand you because it's an unnatural speed. Too fast is worse! Make it a point to slow down slightly when talking on the radio. If you normally talk very. fast, slow way down! When transmitting call signs, addresses, names, and other items that must be remembered, noted, or written down, be a bit more deliberate. The speed at which you transmit should be such that the listener can easily understand and/or take notes. Sending logical phrases at nearly normal reading speed followed by ample pauses to allow the receiving operator to finish writing and the results will be fast, error-free transmissions. You tend to talk faster when emotions run high and things get exciting, but that's just when your message MUST get through! Take a deep breath, get yourself under control, plan what you're going to say, and say it slowly.

Continued - Part 2 next month

EDITORIAL

As I write this it is two weeks since the vicious, cowardly attack on the United States by terrorists forces that are at work around the world.

The attack changed many things for many people including the GARC. Because of the attack the GARC could not hold its General Meeting. The building the meeting is held in was closed because of the attacks.

As a result there are no meeting minutes to publish this month. Instead you will find on page 6 you will find an article written by a Canadian News Man who has nothing but praise for the U.S.

This article was forwarded to me over the internet and I think everyone should have the opportunity to read it.

GOD BLESS AMERICA!!!

The Editor, KA2FEA

TRIBUTE TO THE UNITED STATES

This, from a Canadian newspaper, it's worth sharing. Widespread but only partial news coverage was given recently to a remarkable editorial broadcast from Toronto by Gordon Sinclair, a Canadian television Commentator. What follows is the full text of his trenchant remarks as printed in the Congressional Record:

America: The Good Neighbor.

"This Canadian thinks it is time to speak up for the Americans as the most generous and possibly the least appreciated people on all the earth. Germany, Japan and, to a lesser extent, Britain and Italy were lifted out of the debris of war by the Americans who poured in billions of dollars and forgave other billions in debts.

None of these countries is today paying even the interest on its remaining debts to the United States. When France was in danger of collapsing in 1956, it was the Americans who propped it up, and their reward was to be insulted and swindled on the streets of Paris. I was there. I saw it.

When earthquakes hit distant cities, it is the United States that hurries in to help. This spring, 59 American communities were flattened by tornadoes. Nobody helped. The Marshall Plan and the Truman Policy pumped billions of dollars into discouraged countries. Now newspapers in those countries are writing about the decadent, war mongering Americans.

I'd like to see just one of those countries that is gloating over the erosion of the United States dollar build its own airplane. Does any other country in the world have a plane to equal the Boeing Jumbo Jet, the Lockheed Tri-Star, or the Douglas DC10?

If so, why don't they fly them? Why do all the International lines except Russia fly American Planes? Why does no other land on earth even consider putting a man or woman on the moon? You talk about Japanese technocracy, and you get radios. You talk about German technocracy, and you get automobiles. You talk about American technocracy, and you find men on the moon - not once, but several times - and safely home again.

You talk about scandals, and the Americans put theirs right in the store window for everybody to look at. Even their draft-dodgers are not pursued and hounded. They are here on our streets, and most of them, unless they are breaking Canadian laws, are getting American dollars from ma and pa at home to spend here.

When the railways of France, Germany and India were breaking down through age, it was the Americans who rebuilt them. When the Pennsylvania Railroad and the New York Central went broke, nobody loaned them an old caboose. Both are still broke.

I can name you 5000 times when the Americans raced to the help of other people in trouble. Can you name me even one time when someone else raced to the
Americans in trouble? I don't think there was outside help even during the San Francisco earthquake.

Our neighbors have faced it alone, and I'm one Canadian who is damned tired of hearing them get kicked around. They will come out of this thing with their flag high. And when they do, they are entitled to thumb their nose at the lands that are gloating over their present troubles. I hope Canada is not one of those."

Stand proud, America! Wear it proudly!!

This is one of the best editorials that I have ever read regarding the United States. It is nice that one man realizes it. I only wish that the rest of the world would realize it. We are always blamed for everything, and never even get a thank you for the things we do.

I would hope that each of you would send this to as many people as you can and emphasize that they should send it to as many of their friends until this letter is sent to every person on the web. I am just a single American that has read this.