Troubleshooting Electronic & Electrical Circuits by Frederick Hoehn, copyright 2015, all rights reserved. Chapter 1 Please notice in the title, the word "circuits." The word circuit comes from the same root word as the word circle. When electrical current flows, it flows in a circle. If you have a flashlight, and you turn it on, the electrons flow out of the negative terminal of the batteries, through the light bulb, and back into the positive terminal of the batteries. But what if we change nothing except we disconnect the positive terminal of the batteries? Will you get light from the flashlight? No. Or, what if, instead, we just disconnect the negative terminal of the batteries? Do we get light? No. Why? Because when you disconnected the batteries, you interrupted the circuit. No current flows when we don't have a complete circuit. You must have a circle for the current to flow in, or else you don't have current flow. But not only must we have a complete circuit, but also, there must be a difference in potential (voltage). But in the flashlight, we have a difference in potential from the batteries. But if the batteries are dead, and putting out zero volts, then there's no difference in potential applied to the light bulb, and we get no light. A typical flashlight has two D cell batteries, each providing 1.5 volts of voltage. Two batteries connected in series multiplied by 1.5 volts per battery gives us 3 volts of voltage. So then, the light bulb in that flashlight is a three-volt light bulb. Ohm's law says that E = I x R. Ohm's law is named after George Simon Ohm, who apparently discovered this law of physics. The capital E represents the voltage in volts. The I represents the current in amperes. The R represents the resistance in Ohms. The lower case x means "multiplied by." If you have a 1.5 volt battery, and you connect across its terminals a hundred ohm resistor, then Ohm's law says that .015 amps of current will flow (or, 15 milliamps). A milliamp is one thousandth of an amp. But there's another Ohm's law for Power that says that P = I x E. The power in watts is equal to the current in amperes multiplied by the voltage in volts. If a light bulb is powered by 100 volts, and draws 1 amp of current, then you are using 100 watts of power. At one place where I worked, a supervisor tried to correct me when I spoke of a hundred watt light bulb. He said, "Light is not measured in watts, but in lumens." I didn't argue with my supervisor, but actually light is somewhat measured in watts, because every housewife knows that a hundred watt light bulb puts out more light than a 25 watt bulb in the refrigerator. Troubleshooting electronics and electrical circuits is a matter of applying logical troubleshooting techniques, together with knowledge of how the machine or device is supposed to work, together with the knowledge of electrical principles. Seems like it was a honing machine that I was sent to repair at one factory where I worked. Unfortunately, they didn't have circuit diagrams or wiring diagrams for that machine. So how are you going to repair the machine without drawings? You ask the operator what the machine is doing wrong, and you look for something obvious. On machines such as milling machines that mill away metal, making chips, one thing to look for is whether the chips have accumulated and are interfering with correct operation of limit switches on the machine. I've solved problems by just taking the air hose, squeezing the nozzle, and blowing away chips from the limit switches. But on the honing machine, I really needed the electrical drawings for the machine. "Every prudent man deals with knowledge." So, I proceeded to follow the wiring and drew my own schematic diagram for the machine. On typical machine tools, the wiring is not terribly complicated, unless there's a lot of electronics. If there is an electronic unit, drawings are probably available from the manufacturer. If the machine is controlled by a programmable controller, please see my book, "Ladder Logic & Programmable Controllers." After making my drawing of the wiring of the honing machine, I was able to pinpoint and correct the problem. At a factory in Northern California, a fellow maintenance man, a Mechanic, came to me and said that he had been working on this lathe for about an hour, and didn't seem to be getting anywhere, so he thought the problem might be electrical. I went with him to the lathe and saw that the controls had a plug-in relay, probably it was an octal relay with eight pins, that plugged into a socket. Any time you have something that plugs in, or two connectors that plug together, there is the possibility of a bad connection. The pins of the connector will oxidize over a period of time, and oxidized metal doesn't make for good connections. In the oxidizing process, the metal combines chemically with oxygen from the air, making a metal oxide. So, clean off the dull metal with a little scraping, and then your shiny metal will make a better connection. I went to that plug-in relay at the lathe, and moved it a little out of its socket, then pushed it back in, repeating the process several times, and the lathe started working right. Just a bad connection. Chapter 2 At another factory where I was working, a machine was down. I was sent to work on it. The Maintenance department had called the field representative of the machine manufacturer. I was sent out to work with him on the machine. He was a rather young man, and I was probably a couple of decades older, so I took the lead. An oscilloscope will display waveforms of what's happening in the machine. You connect the alligator clip of the 'scope probe to ground on the machine (the chassis or metal frame.) Then put your probe where you want to get information in the circuit. If the ground connection on the probe isn't long enough, use additional clip leads with alligator clips. Looking at the schematic diagrams, I saw places in the circuit where I expected that I should see some square waves. But the square waves that should have been there were absent. So, I moved the probe farther upstream. Square waves should have been coming out of the two quartz crystal oscillators of the machine. But still no square waves. I noticed that the machine had two quartz crystals plugged into their sockets. I reached over and did with those two crystals as I had done with that plug-in relay, and the machine started working right. Bad connection. I remember reading of some scientists, from years ago, that were working with electrical apparatus. There was an older scientist who had set up his apparatus on a table. He had invited a younger man who seemed to be very bright. But the darn thing wasn't working. The younger man had seen a situation like that before. He reached out and gave the table a good bang, and the thing started working. Bad connection. The older scientist was pleased and impressed. I applied to a company for a plant maintenance job, and got an interview. At the interview, the fellow showed me a schematic diagram, a ladder diagram. Ladder diagrams have the two vertical lines for control voltage, and then horizontal rungs for the various switches, sensors, and anything else being used for control. The guy asked me to troubleshoot the problem as if I had a voltmeter to use. I was to tell him where I would put my voltmeter probes, and he would tell me what voltage I would measure there. The trouble seemed to be in the area of a certain limit switch that was operated by a door. I said I'd put the negative probe on the negative terminal of the control voltage source. I put the other probe on one side of the limit switch, and he said, yes I have the control voltage there. I put the probe on the other side of the limit switch, and he said, no, you have zero volts. I said, "The limit switch is open, probably because the door that operates it is open." He told me, "You're right." In the U.S. Navy, my ship had AN/GRC-27 transceivers. One of them had been down for a couple of months. The transceiver was a tall rack of equipment. I looked at the top, perhaps standing on a box to get me higher, and I saw a loose wire connected at one end but not at the other end. It looked like it had probably broken off a grounding clip. I grounded the loose end of the wire, and the transceiver started working. I also served one enlistment in the Army. When I got to Direct Support Detachment located at the city of Oui Jong Bu, Republic of Korea, there was a building like a large warehouse. There was a radar sitting over in one corner of the building, and I was told that no one had been able to repair that radar for three months. I was not assigned to repair that radar, but after my normal day's work, I went to the radar to make the repair. It took maybe three days in my off-duty hours. The radar antenna would rotate even with the rotation switch off. When you turn the rotation switch off, the antenna rotation should stop. You make voltage measurements by applying your voltmeter probes to the circuit. If your voltmeter has a high input impedance, such as with Field Effect Transistors in the input, then the voltmeter should not interfere with the circuit you're measuring. But to make current measurements, you open the circuit (with the power off) and insert the ammeter in series with the circuit. (However, there are "clamp on ammeters" that can be used to measure current in alternating current circuits just by sensing the magnetic field.) I found that there was about one ampere of current flowing where there should have been zero. That's why the antenna was rotating. But where was it coming from? I followed the schematic circuit diagram to the various places connected to that circuit that had excessive current flow. One of those places was a multipin connector on the exterior of the radar. You open a panel, and you can see the rear of the connector, where the wires are connected to it. But your view of the rear of the connector is obscured by a rubbery boot that is over the rear of the connector. I pulled back the rubbery boot, and there was the problem. Evidently, that connector had been replaced in the field, and someone had done just a terrible job of soldering the wires on to the connector. Someone that for practical purposes, didn't know how to solder. People at the Raytheon factory don't do soldering that bad, or they'd lose their jobs. There were blobs of solder, causing one or more "short circuits." I walked thirty yards over to the parts department where my friend, Sgt First Class Catlett was working, and told him I had found the problem. My Dad taught me how to solder when I was about twelve, and I corrected the bad soldering, and the radar was fixed. I am a graduate of U.S. Navy Electronic Technician "A" School, and got a lot of good training there. But in addition, I've read books pertaining to electronics, computers, programming, electrical motors, three-phase electrical circuits. You can learn a lot by reading books, and gain favor with your supervisor when he sees that you can fix about anything he sends you to fix. A very good author of electronics books is Mr. Malvino. Seems like he's an Instructor at one of the community colleges. I've seen one or more of his books at the public library. Chapter 3 At a company in Houston, TX, I worked in the Engineering Department as a Computer Programmer. I worked with three hardware Engineers. I was the software guy. We had an excellent tool at our disposal, the Hewlett Packard 64000 Development System. I took the time to read the manuals for the development system. Though I was non-degreed, degreed Engineers would come and ask me how to do things with the development system because I had read the manuals. You should read the manuals that come with your equipment. A job opened up for me with a TV station to be a TV station Engineer. But they told me I would have to get my FCC license. So I bought the book for the Third Class license, studied the book, then went to the FCC office in Los Angeles, took the test, and passed. Bought the book for Second Class license, studied the book, then took the test, and passed. Bought the book for First Class license, studied the book, then took the test and passed. I became the main operator of that TV station. I helped them build the transmitter, and drew a schematic diagram of it. As I did so, I found and corrected some wiring mistakes. We first went on the air in about Fall or Winter. But when Spring arrived, and warmer weather, the transmitter's high voltage power supply started blowing out expensive "doorbell diodes," so-named because of their doorbell shape. At one staff meeting, the Manager said, "We may have to go dark because of this problem." It was a Christian TV station, built by a church in Southern California. I answered, "That can't be the will of God." On a day when it was my duty to broadcast the daily programming, I went up early to the transmitter on the mountain. The high voltage wiring was easy to identify. It had a white Teflon insulation. I followed that wiring wherever it went, looking for black burn marks that would indicate a short circuit and arcing. But found none. I removed the cabinet blower from the door of the high voltage cabinet, and mounted it on a ladder blowing directly at the doorbell diodes. They didn't blow out anymore. Later, the Chief Engineer got us another blower for that, and the cabinet blower went back into the door. I was working at a factory in Illinois, and was sent to work on a machine. The problem seemed to be in the area of a relay or solenoid, I'm not sure which, this many years later. One side of the control voltage was grounded to the metal cabinet. When you wind enameled wire on a spool to make a coil, perhaps with an iron core, now you have the two ends of the wire. To have a complete circuit, both ends of the wire must be connected to something. With the voltmeter, I measured the full control voltage at one terminal of the coil. Then, at the other terminal of the coil, I measured the same control voltage. How can you measure the same control voltage at both terminals of the coil when one side of the coil is supposed to be grounded? Well, you can't. The ground connection for the coil had been lost, and that's why it wouldn't activate. The manufacturer had used a rather flimsy method of grounding the ground wires, and one wire had come loose. I used a better method, employing wire nuts. The problem was solved. For troubleshooting, you need knowledge of electrical and electronics principles. And then you need knowledge of how the machine or device is supposed to work. You'll need a digital multimeter, and sometimes, and oscilloscope is very useful. But the employer may provide the test equipment. When troubleshooting, the "half split rule" is often helpful. On your schematic diagram or block diagram, you have inputs, generally at the left or top, and you have outputs, generally at the right or bottom. If something's wrong, and you have good inputs, but bad outputs. Now divide the diagram about in half, and make your measurements. If they seem good, then continue to the right or toward the bottom to make your next measurements, again applying the half split rule. But if those measurements were wrong, then continue upstream to the left or toward the top for your next measurements. The half split rule can be a time saver in solving problems.