Electronics Troubleshooting Manual
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As an industrial electrician, you'll encounter many complex electrical circuits and drives that will break down as they age. Chances are, you won't be an expert in repairing these devices, but you can take some practical steps to solve problems and help get your systems operational again in a timely manner.
Let's start with the motor drive. Solid-state electronic AC motor drives are becoming more common within industrial plants. They control a wide variety of devices like pumps, conveyors, air handlers, chillers, machine tools, mixers, and a host of other devices once designed to run at constant speed or be powered by DC. Since failure in these devices can be often attributed to the rectifier section, you'll need a fundamental understanding of transistors, diodes, silicone controlled rectifiers (SCRs), and insulated gate bipolar transistors (IGBTs). Pulse width modulated (PWM) inverter drives are the most prevalent type of AC drives ( Fig. The AC line voltage is converted to DC (in the converter section) and then reconstructed back into a variable frequency and a variable voltage output.
Changing the frequency varies motor speed, and motor torque is maintained by keeping the ratio of volts-to-frequency at a constant. Troubleshooting motor drives. Because most failures occur within the power sections instead of the circuit boards, they aren't very difficult to troubleshoot. The typical plant maintenance technician will rarely see enough failures to build up any proficiency in repairing circuit boards. Effective troubleshooting on a variable frequency drive (VFD) requires a methodical approach. The classic divide-and-conquer method, taught by most technical schools, is effective when knowledge of the equipment is limited. A good troubleshooter will first isolate the box or section that isn't passing the signal and then work on it.
So how can you quickly and efficiently troubleshoot a dead VFD? Remember to always put safety first. The capacitors within the power section can maintain a dangerous charge even after the power is removed. First make sure that the capacitors are discharged before putting your hands into the power section.
With the power off, begin checking the power sections of the drive. Then, place your digital multimeter (DMM) in the diode check mode. Find the positive DC bus (sometimes this may be brought out to a terminal), place the negative (black) lead from your DMM on it, and then check each incoming phase in turn with the positive (red) lead. You should read a diode drop of about 0.6V on each phase. If it reads open, then the charge resistor is open and needs to be replaced. This is a common source of many problems. Next, place the DMM's positive lead on the negative bus and the negative lead on each incoming phase in turn as you did before.
You should read a diode drop, not a short or an open. Place one DMM input lead on the positive bus and the other on the negative bus. On this measurement you should read the capacitor charging rather than a short. To check the inverter section, place the positive DMM lead on the negative bus and the negative lead on each output phase. You should read a diode drop because diodes are connected across each output transistor.
Again, you shouldn't read a short. Check the remainder of the inverter section by placing the negative lead of the DMM on the positive bus, checking each output phase again with the positive lead of the DMM. You should read a diode drop again and not a short. If you read OPEN from either of these checks then the bus fuse is most likely open. If no problems are present within the power section and the unit still won't function, it's either improperly connected or programmed or has a bad circuit board.
Newer PWM drives use IGBTs in the driver sections of the output, and are much less likely to fail. These devices perform like a metal-oxide semiconductor field effect transistor (MOSFET). When the voltage at the gate exceeds the threshold voltage, the device turns on. If the voltage applied to the gate contact is less than the threshold voltage V th, then the device is turned off ( Fig. Visual PLC troubleshooting techniques.
Most PLCs incorporate light emitting diodes (LEDs) in their design, which offer a good source of diagnostics. They can provide valuable information about the wiring, and input/output (I/O) modules within the unit. Typically, I/O modules have at least one LED indicator; input modules normally have a power indicator, while output modules usually have a logic indicator. A lit power LED on an input module indicates that the input device is operating and its signal is present at the module. However, this indicator by itself can't isolate malfunctions to the module.
Consequently, some manufacturers provide an additional diagnostic indicator known as a logic indicator. If a logic LED is lit, the logic section of the input circuit has recognized the presence of the input signal.
If the logic and power indicators don't match, then the module is unable to correctly transfer the incoming signals to the processor. This indicates a module malfunction and most likely points to the problem area. The output module's indicator functions in a similar fashion to the input module's indicators. When on, the logic LED indicates that the module's circuitry has acknowledged a command from the processor to turn on. In addition to the logic indicator, some output modules incorporate either a fuse indicator or a power indicator, or sometimes both.
A blown fuse indicator displays the status of the protective fuse in the output circuit. The power indicator displays that power is being applied to the load. Similar to the power and logic indicators in the input module, if both LEDs aren't on simultaneously, the output module is malfunctioning — again pointing to the probable problem area. As you can see, LED indicators greatly assist the troubleshooting process. With power and logic indicators, you can immediately pinpoint a malfunctioning module or circuit.
Although they can't diagnose all problems, they serve as a good first round indicator of a system malfunction. Troubleshooting the PLC inputs. If the field device connected to an input module doesn't seem to turn on, a problem may exist somewhere between the line connection and the terminal connection to the module. First place the PLC in standby mode so the output isn't activated. This will permit you to manually activate the field device. A limit switch can usually be manually closed to achieve this result. When the field device is manually activated, the module's power status indicator should turn on, indicating the power link is working properly.
If this occurs, then the wiring most likely isn't the root of the problem. Next, analyze the reading of the PLC's input module. Place the PLC in its test mode.
The device should read its inputs and execute its program, but not turn on its outputs. If the PLC reads the device correctly, then you know the problem isn't located in the input module.
If it doesn't read the device correctly, then the module could be defective. However, several causes are possible. First, the logic side of the module may not be operating correctly. Second, its optical isolator may be blown. Third, one of the module's interfacing channels could be damaged. Vw golf 7 tdi full option photo.
Television Troubleshooting
In any case, you'll need to replace the module. If the module doesn't read the field device's signal, then further tests are required. Bad wiring, a faulty field device, a faulty module, or an improper voltage between the field device and the module could be causing the problem. First, measure the voltage to the AC input module. Your DMM should be in voltage measuring mode and should display the voltage that powers the module. If the voltage is present and at the correct level, you know you have a bad input module because it's not recognizing the applied voltage.
If the measured voltage is 10% to 15% below the specified signal voltage, then the problem most likely is in the source voltage to the field device. If no voltage is present, then the wiring is broken or shorted or the field device is dragging it down. Check the wiring connection to the module to ensure that the wire is properly secured at the terminal or terminal blocks. You can also perform an insulation check on the wiring to look for shorts and/or damaged insulation. Be sure that the system is de-energized first before conducting this test. To further locate the problem, confirm that voltage is present at the field unit.
With the device turned on, measure the voltage across it using your DMM. If no voltage is present on the load side of the unit (the side that connects to the module), then the input device is probably defective. If there is power, then the problem is in the wiring from the input device to the module. In this case, the wiring must be inspected and tested to find the problem. Troubleshooting PLC outputs. The first step in troubleshooting the outputs is to isolate the problem to either the module, the field device, or the wiring. First check that the source of power to the output module is at the specified level.
This value should be within 10% of the rated value. In a 120VAC system, for example, it should be between 108VAC and 132VAC. Examine the output module. If the fuse is blown, check its rated value to be sure the correct fuse was installed in the first place. Also, check the output device's current specifications to determine if the device is pulling too much current. If the module's output status indicator fails to turn on despite receiving the instruction to turn on from the central processing unit, it's faulty. If the indicator does turn on and the field device doesn't activate, then check for voltage at the output terminal to be sure that the switching device is, in fact, operational.
If no voltage is present, then you should replace the module. If voltage is present, then the problem lies in the wiring or the field device. At this point, make sure the field wiring to the module's terminal or to the terminal block has a good connection and that no wires are broken. This can be accomplished in the same fashion as described earlier. When you finish checking the output module, check to see that the field device is functioning correctly. Check the voltage coming to the field device while the output module is on. If voltage is present, but the device doesn't respond, then the field device is probably defective or damaged.
One trick for checking the field device is to test it without using the output module. Remove the output wiring and connect the field device directly to the power source. If the field device doesn't respond, then it's faulty. If the field device responds, then the problem lies in the wiring between the device and the output module.
Check the wiring, as noted earlier, looking for broken wires, shorts, worn insulation, and oil or grease on the connection points and along the wiring route. Troubleshooting the CPU. PLCs also provide diagnostic indicators that show the status of the central processing unit (CPU). These indicators include such display messages as POWER OK, MEMORY OK, and COMMUNICATIONS OK.
You should first check that the PLC is receiving enough power from the transformer to supply all the loads. If the power received is in accordance with specifications and the PLC still isn't working, check for a voltage drop in the control circuit or for blown fuses. If these conditions are all proper, then the problem lies in the CPU. Most likely, the diagnostic indicators on the front of the CPU will display a fault in either memory or communications mode. Should one of these indicators be lit, it's highly likely that the CPU needs to be replaced.
Troubleshooting the input and output sections of a motor drive can be easy when approached logically and addressed section by section. All you need to do is measure volts and ohms with a DMM. As with motor drives, the most practical method you can use to diagnose PLC input/output malfunctions is to isolate the problem to either the wiring, the module, or the field device.
Basic Electronics Troubleshooting
When these systems have both power and logic indicators for you to view and interpret, then module failures become very easy to recognize and isolate. Olobri is a product development manager for AEMC Instruments, Foxborough, Mass.
Skill Level: Beginner by November 29, 2010 Good troubleshooting skills are vital to the electronics hobbyist. More often than not, a circuit is not going to work perfectly on the first try, especially as a beginner.
It can be very intimidating when a component on a board gets hot, exhibits unexpected behavior, does nothing at all, or even explodes. Where does one start troubleshooting? The answer is different for every situation and even with practice one will come across errors that can't be immediately explained. Jedi-like troubleshooting skills come only with experience, but there are some common problems that can be diagnosed quickly, and understanding these common problems and how to check for them is a starting place common to beginners and masters. Let's say you plug in your circuit, and something is wrong. It could be not working at all, or behaving in a way that you don't expect.
There are issues you should ALWAYS check for before you even get out the multimeter. These may seem obvious, but it's better to start simply than troubleshoot more complex issues for hours just to find a silly mistake. Is power connected correctly?
Connecting ground to a power connection and power to a ground connection (rather, positive to negative and negative to positive) can damage a device and will obviously not allow for proper behavior. Check for it. Even the most experienced professionals will do this from time to time. Are the components soldered correctly? If an LED isn't lighting up, maybe the orientation of the LED is incorrect. Is your square-shaped device soldered so that Pin 1 is where it's supposed to be?
Check for this early. Performing hours of troubleshooting to finally discover that a chip is on backwards is about as frustrating as it gets. Are there solder jumpers/shorts on the board? Check your chips for solder jumpers between pins.
A quick visual inspection can be worth hours of debugging good code. Are there bad solder joints? One bad solder joint can hork an entire circuit. Make sure they are all nice and shiny, and that the pins of a surface mount device are actually touching the pad on the board and not just floating above with solder on them. So - you've preformed all of the tests above and something is still not working. This indicates a potentially more complex problem, but still there are some general tests one should perform before hooking up the logic analyzer. Is the board bad?
This happens every now and then. Perform a continuity test between the VCC and Ground traces on the board. Rather than risk damaging your devices, make sure that the ground signals on the board are not shorting to VCC because of a board defect. Are your components the correct values?
A perfectly soldered resistor is no good if it's not the correct value. Maybe you accidentally used the 12MHz clock instead of the 16MHz you meant to use. The above tests can all be performed in about two minutes, and even though they're simple (and it hurts a designer's ego to find out she/he made such a simple mistake) they rule out the biggest common issues with improperly functioning circuits. If a circuit passes all these tests, then one can start digging into manuals, debugging code, and checking voltages with a multimeter with the knowledge that the error is not due to a simple common problem. Example question: You have a circuit board with the circuit shown below.
You power the device, and the LED lights up, but when you attempt to program the ATTiny, the programming fails. The ATTiny chip is soldered in the correct orientation.
Which of the following should you do next? A) Check the VCC and GND traces on the board for a short B) Check that the 330 Ohm resistor is the correct value C) Inspect the soldering of the chip for cold joints and jumpers Answer: C The LED is functioning properly, so you know that there is no short from VCC to GND on the board. The LED is lighting up, so the resistor is probably the correct value. The ATTiny is in the correct orientation, so if it's not programming, it's likely not soldered properly to the board. A single cold solder joint will cause bad connectivity and not allow programming. Check the board for 'gray' (as in not shiny) solder joints, as this is usually indicative of an incorrectly soldered pin. Two that have served me well: check to make certain that a single ground is being referenced by the whole system (particularly if two devices appear to function, but won’t “talk”), and feel around too see what is too hot and what is too cold.
When I had a “you can have this if you can make it work” opportunity many years ago, I used the latter one to find which chip of the hundred or so in an Apple II was reversed (it turns out that there is exactly one which has text facing the back instead of the keyboard when inserted correctly, and it had been “fixed”). The computer still works, btw, Hardy chips back then. Oh yeah, and are any batteries present still near their nominal voltage, or are they worn out. Near the end of a long debug, there’s always this new failure that crops up. Failing to connect power is my number one point of failure. Even after I’ve double-checked it, it turns out I needed to triple check it.
So, for every chip I’ve installed, I’ve been pulling out a multimeter and probing the power pins as close as possible to chip, to make sure they’re getting the proper voltage. The other day, I lost about four hours trying to debug a problem with a XBee. First I probed the power connections where I soldered the pins to the PCB, and they seemed fine. Four frustrating hours later, I probed the solder connections on the XBee itself (probing as close to the chip as possible) and I discovered that my connector was faulty. Also, for more debugging, I highly recommend this book: http://www.amazon.com/Debugging-Indispensable-Software-Hardware-Problems/dp//ref=sr11?ie=UTF8.