When repairing equipment and assembling circuits, you always need to be sure that all the elements are in good working order, otherwise you will waste your time. Microcontrollers can also burn out, but how to check it if there are no external signs: cracks on the case, charred areas, a burning smell, and so on? For this you need:
Voltage stabilized power supply;
Multimeter;
Oscilloscope.
Attention:
A complete check of all the microcontroller nodes is difficult - the best way is to replace it with a known good one, or to flash another program code with the existing one and check its execution. In this case, the program should include both a check of all pins (for example, turning the LEDs on and off after a specified period of time), as well as interrupt circuits and others.
Theory
This is a complex device with multifunctional units:
power circuits;
registers;
inputs-outputs;
interfaces and so on.
Therefore, when diagnosing a microcontroller, problems arise:
The operation of the obvious nodes does not guarantee the operation of the rest of the components.
Before proceeding with the diagnosis of any integrated microcircuit, you need to familiarize yourself with the technical documentation to find it, write in the search engine a phrase like: "datasheet element name", as an option - "atmega328 datasheet".
On the very first sheets you will see basic information about the element, for example, consider some points from the datasheet for the popular 328th atmega, for example, we have it in a dip28 package.It is necessary to find the pinouts of microcontrollers in different packages, consider the dip28 we are interested in.
The first thing we will pay attention to is that pins 7 and 8 are responsible for the plus of the power supply and the common wire. Now we need to find out the characteristics of the power supply circuits and the consumption of the microcontroller. Supply voltage from 1.8 to 5.5 V, current consumed in active mode - 0.2 mA, in low power mode - 0.75 μA, while 32 kHz real time clock is on. Temperature range from -40 to 105 degrees Celsius.
This information is enough for us to carry out basic diagnostics.
Main reasons
Microcontrollers fail, both due to uncontrollable circumstances and due to mishandling:
1. Overheating during operation.
2. Overheating during soldering.
3. Overload of conclusions.
4. Power supply polarity reversal.
5. Static electricity.
6. Bursts in power circuits.
7. Mechanical damage.
8. Exposure to moisture.
Let's consider each of them in detail:
1. Overheating may occur if you operate the device in a hot place, or if you have placed your design in a too small case. The temperature of the microcontroller can also be increased by too tight installation, incorrect wiring of the printed circuit board, when there are heating elements next to it - resistors, power circuit transistors, linear power stabilizers. The maximum allowable temperatures of common microcontrollers are in the range of 80-150 degrees Celsius.
2. If you solder with a too powerful soldering iron or keep the tip on the legs for a long time, you can overheat the micron. Heat through the pins will reach the crystal and destroy it or connect it to the pins.
3. Overloading of terminals occurs due to incorrect circuitry solutions and short circuits to ground.
4. Polarity reversal, i.e. supplying Vcc with a power supply minus, and a plus at GND, may be the result of improper installation of the IC on the printed circuit board, or incorrect connection to the programmer.
5. Static electricity can damage the chip, both during installation, if you do not use anti-static paraphernalia and grounding, and during operation.
6. If a failure occurs, the stabilizer has broken through, or for some other reason a voltage higher than the permissible voltage was applied to the microcontroller - it is unlikely to remain intact. It depends on the duration of the exposure to the emergency.
7. Also, do not be too zealous when installing a part or disassembling the device, so as not to damage the legs and the body of the element.
8. Moisture causes oxides, leads to loss of contacts, short circuit. Moreover, we are talking not only about the direct hit of liquid on the board, but also about long-term work in conditions with high humidity (near water bodies and in basements).
Checking the microcontroller without tools
Start with an external inspection: the case must be intact, the soldering of the leads must be flawless, without microcracks and oxides. This can even be done with a regular magnifying glass.
If the device does not work at all, check the temperature of the microcontroller; if it is heavily loaded, it can heat up, but not burn, i.e. the temperature of the case should be such that the finger endures with a long hold. You can't do anything else without a tool.
Check to see if voltage is being applied to the Vcc and Gnd pins. If the voltage is normal, you need to measure the current, for this it is convenient to cut the track leading to the Vcc power pin, then you can localize the measurements to a specific microcircuit, without the influence of parallel connected elements.
Do not forget to strip the board cover down to the copper layer where you will touch the probe. If you cut it carefully, you can restore the track with a drop of solder, or with a piece of copper, for example, from a transformer winding.
Alternatively, you can power the microcontroller from an external 5V power source (or other suitable voltage), and measure the consumption, but you still need to cut the track in order to exclude the influence of other elements.
To carry out all measurements, we have enough information from the datasheet. It will not be superfluous to see what voltage the power regulator for the microcontroller is designed for. The fact is that different microcontroller circuits are powered by different voltages, it can be 3.3V, 5V and others. Voltage may be present but not correct.
If there is no voltage, check if there is a short circuit in the power supply circuit and on the other legs. To quickly do this, turn off the power to the board, turn on the multimeter in continuous mode, put one probe on the common wire of the board (ground).
Usually it runs along the perimeter of the board, and there are tinned pads or on the connector bodies at the attachment points with the case. And the second one, pass through all the pins of the microcircuit. If it beeps somewhere - check what kind of pin it is, the dialing should work on the GND pin (8th pin on atmega328).
If it does not work, the circuit between the microcontroller and the common wire may be broken. If it worked on other legs - see the diagram for any low-resistance resistance between pin and minus. If not, you need to unsolder the microcontroller and call again. We check the same thing, but now between the plus of the power supply (with the 7th pin) and the pins of the microcontroller. If desired, all the legs are called among themselves and the connection diagram is checked.
The eyes of the electronics engineer. With it, you can check the presence of oscillation on the resonator. It is connected between the XTAL1,2 pins (pins 9 and 10).
But the oscilloscope probe has a capacitance, usually 100 pF, if you set the divider to 10, the probe capacity will drop to 20 pF. This changes the signal. But for the performance check it is not so important, we need to see if there are any fluctuations at all. The signal should have a shape like this, and a frequency appropriate for a particular instance.
If the circuit uses external memory, then it can be checked very easily. On the data exchange line there should be packets of rectangular pulses.
This means that the microcontroller correctly executes the code and communicates with the memory.
If you unsolder the microcontroller and connect it to the programmer, you can check its response. To do this, in the program on the PC, click the Read button, after which you will see the ID of the programmer, on the AVR you can try to read the fuses. If there is no read protection, you can read a firmware dump, load another program, test the operation on a code you know.This is an effective and easy way to diagnose microcontroller malfunctions.
The programmer can be either specialized, such as USBASP for the ATS family:
And universal, such as Miniprog.
Conclusion
As such, checking the microcontroller is no different from checking any other microcircuit, except that you have the opportunity to use the programmer and read the information from the microcontroller. So you will be convinced of its connectivity with a PC. However, malfunctions do occur that cannot be detected in this way.
In general, the control device rarely fails, more often the problem lies in the strapping, so you should not immediately go to the microcontroller with all the tools, check the entire circuit so as not to get problems with the subsequent firmware.
?- In-circuit diagnostics of electronic components, PCB assemblies and electronic devices
- Out-of-circuit diagnostics of electronic components
- In-circuit functional and logical testing of electronic components and devices
- Out-of-circuit functional testing of electronic components
- Measurement of electrical characteristics of electronic components and devices
- Programming and verification of the contents of EEPROM chips
- Determining the functions of unknown digital circuits
- Detection of counterfeit electronic components
- Programming, testing and debugging of microcircuits and devices operating on the JTAG interface
- Reconstruction of the schematic diagram and connection diagram of devices based on printed circuit boards in the absence of design documentation
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In amateur and professional practice, it is often necessary to check the serviceability of simple digital microcircuits. It is hardly advisable to use complex logic testers and analyzers for this. It is quite possible to get by with a tester to check the logic elements of various microcircuits.
The logic tester of simple digital combinational logic microcircuits allows you to check the serviceability of each individual logic element (LE) of the microcircuit with the logical functions of two input variables 2I, 2OR, 2EXCL. OR and their inversions for the popular TTL and CMOS series. These include microcircuits of functional types LAZ, LA8, LA9, LA11-LA13, LA18, LA21, LA23; LE1, LE5, LE6, LE10, LE11; LI1, LI 2, LI8; L L 1, L L 2, LL4; L P 5, L P 8, LP12; TLZ series TTL (TTL Sh) K155, K158, K131, K531, K555, KR1531, KR1533 and others, as well as series CMOS KR1554, 74 NS (1564) and types KTZ, LA7, LE5, LI2, L P 2, LP14, TL1 series CMOS K176, K561, 564, KR1561. The device allows you to determine the logical function (within six specified) and pinout of microcircuits with two-input LE. In addition, the tester can check the serviceability of bipolar transistors, diodes and various pn junctions.
Simplicity of design and ease of use, along with rather wide functionality and compact design with autonomous power supply from the Korund battery, allow using this device not only in an amateur radio laboratory or, for example, when buying devices on radio markets, but also for incoming control when small-scale production of electronic equipment.
The tester circuit is shown in the figure. A pulse generator on DD1.1, DD1.2 with a frequency of about 20 Hz forms a periodic test sequence of logical signals using two binary frequency dividers on the triggers DD2.1, DD2.2 to form a truth table of a logical function of two input variables - 00, 01, 10, 11. From this test sequence, reference signals of logical functions 2I (DD3.1 element), 2EXC.OR (DD1.3 element) and 2OR (DD3.2, DD3.3 elements) are formed. The function is selected with the SB3 switch, the DD3.4 element inverts the function signal, and the function inversion is selected with the SB4 switch (for example, 2I-NOT, as shown in the figure).
If the tested and reference logical signals are equal, the output signal of the comparison LE is equal to zero and the LED is off. If the tested and reference signals are different, then the high output level corresponding to the erroneous tested signal of the LE of comparison turns on the LED, indicating the failure of this LE (more precisely, the difference between the logical function of the element and the reference).
To facilitate the identification of a faulty LE, it is convenient to place the LEDs near the corresponding terminals of the tested microcircuit (conventionally shown in the right field of the figure) of the contact panel with DD5. With a fully functional DD5 microcircuit, all LEDs are off, and in case of an error in at least one LE, one or more LEDs will blink or constantly light up, signaling a malfunction. Thus, this logic tester will allow you to identify one faulty LE while the rest are valid, which may be useful in amateur radio practice.
Switches SB1 and SB2 select the pinout of the tested microcircuit in accordance with the given table (the figure shows the position of the switches SB1, SB2 for testing the LA7, LE5, LP2 and other CMOS series - K176, K561, 564, KR1561). If the pinout or logical function of the tested microcircuit is unknown, then they can be determined (within the functionality of this tester) by going over the positions of the switches SB 1, SB2, SA3. SB4.
This logic tester can also check the health of bipolar transistors, diodes and various pn junctions. For this, elements SB5, R17, R18, HL6 t HL7 and clamps for connecting transistors "E", "B", "K" and diodes "VD" are introduced into the circuit.
Switch SB5 switches the tester from the microcircuit test mode (shown in the diagram) to the transistor test mode. When the SB5 switch is in the upper position, the reference logic level is fed only to the element DD4.4, and the terminals of the emitter "E" and base "B" through the resistors R17, R18 are "interrogated" by the signals of the test sequence from the non-inverting outputs of the triggers. The other input of the comparison element DD4.4, connected to the terminal "K" (collector), through the resistor R16 receives a level antiphase to the "emitter" (from the inverse output of the trigger DD2.1).
|
Position title |
SB1 position |
Position SB2 |
Chip series |
CMOS: K561, K170, 564, KR1561 |
TTL / TTLSh: K155, K555, 133, 533, K531, KR1533, KR1531, etc. CMOS: KR1554, 74NS (1564) |
Panel pinout: input, input-output |
1,2 = 3 5, 6 = 4 8, 9= 10 12, 13* 11 |
2, 3 = 1 5, 6 = 4 8, 9= 10 11, 12= 13 |
1,2 = 3 4, 5 = 6 9, 10 = 8 12, 13= 11 |
Tml (microcircuit logic function) |
LE5 (OR NOT) LP2 (EXC. OR) LP14 (EXC. OR) TL2 (AND-NOT) |
LAV (AND-NOT) LE1 (OR-NOT) LE5 (OR-NOT) LEB (OR-NOT) LEU (OR-NOT) LE11 (YLI-NOT) |
LAZ, LA9 (I-NOT) LA11, LA13 (I-NE) LA21, LA23 (I-NE) LA18, TLZ (I-NE) LI1, LI2, LI8 (I) LL1, LL2 (OR) LP5, LP12 (EXC. OR) LP8 (check by OR function) |
When connected to these terminals of the same terminals of a working transistor, a periodic signal is formed on its collector, corresponding to the logical function 2OR-NOT for transistors of the structure p-p-p and 2I-NOT for transistors of the structure p-p-p, i.e. the choice of the type of conductivity of the tested transistor carried out by switches SB3, SB4. In one of the four phases of the polling signals, the transistor is switched on according to the common emitter circuit (if we neglect the protective resistor R17), while the resistor R18 sets the base current of the transistor, and the resistor R16 is its collector load.
Simultaneously, the test sequence from the non-inverting outputs of the triggers DD2.1, DD2.2 is fed to the inputs of all LEs of the tested microcircuit DD5 located in the contact panel XS1. Transistors VT1, VT2 amplify the low logic level current to a value sufficient to connect four LE inputs of the TTL K155, K531 and others series. Resistors R4-R11 protect the device and the tested microcircuit if it is turned on incorrectly, exclude the influence of faulty (short-circuited to the power leads) microcircuit inputs on other input circuits and additionally limit the value of its input currents. If the tester is used to test microcircuits of only CMOS series, then the resistance of the resistors R4-R11 is better to increase to 1 MΩ to control input currents of the order of 1 μA, and the elements VT1, VT2, R2, R3 can be excluded.
The output signals from the tested LE of the DD5 microcircuit are fed to the inputs of the LE comparison of the DD4 microcircuit. Resistors R13-R16 check the load capacity of the DD5 outputs (for CMOS microcircuits) and are necessary for checking LEs with open collector outputs (TTL). The reference signal of the selected logic function from the SB4 switch is supplied to the other inputs of the comparison LE, and the HL1-HL4 LEDs are connected to the comparison LE outputs, and current-limiting resistors for the LEDs are not needed, since the output current of the DD4 microcircuit is limited to a few milliamperes.
If the current amplification factor of the base of the tested transistor is less than 0.6R18 / R16 (for the indicated ratings - less than 10), then the tester will consider it faulty. By changing the resistance of the resistor R18, you can set the criterion for selecting transistors by the current amplification factor. Thus, with a suitable transistor, all LEDs will be off, and in other cases, the HL4 LED will blink.
A diode tester with automatic polarity detection is similar to that described in. When a diode (or any rectifying junction) is connected to the "VD" terminals, the one of the LEDs HL6, HL7, which is turned on in the same direction as the diode, will blink in arbitrary polarity, indicating the polarity of its turning on. In the event of a short circuit in the diode, both LEDs flash, and in the event of an open circuit, none of them flash.
The tester's power supply must be rated for a maximum output current of at least 150 mA with an output voltage of at least 7.5 V. To test CMOS microcircuits, it is possible to supply power from a Korund battery, since in this case the tester's current consumption from the battery does not exceed 5 mA. The supply voltage of the +5 V tester microcircuits is stabilized by the DA1 microcircuit. On the elements VT3, R12, a unit for limiting the current consumption of the tested microcircuit is assembled at the power output (pin 14 DD5) at a level of 100 mA to protect the tester if the tested microcircuit is turned on incorrectly or if it is "broken" through the power circuit. The current limitation occurs due to the transition of the transistor VT3 from saturation mode (with a working DD5 microcircuit) to the normal mode of amplification of the drive at a base current fixed with the resistor R12. The limiting current is determined by the current gain of the transistor VT3 and the resistor R12 and can be changed. Elements DD1.4, HL5 are designed to indicate the current limiting mode. The tester power switch (not shown in the diagram) can be combined with the SB1, SB2, SA3 switches or linked to the panel lever to automatically turn off the tester when changing chips.
Microcircuits DD1-DD4 are replaceable with analogs from the KR1661 or 564 series; DA1 - KR1157EN5 with any letter index or KR142EN5A; transistors VT1, VT2 - types KT315, KT3102 and VT3 - types KT209, KT345, KT501, KT626, KT814 with any letter index. And ^ other transistors with a low saturation voltage collector-emitter are used, it is only necessary to select the resistance of the resistor R12. Permissible deviations in the ratings for resistors are 20%, for capacitors - up to 100%. Switches SB1, SB2, SB4, SB5 - any, for example, P2K, and SA3 - PD21 -3.
It is desirable to use the panel with zero force (lever clamp). To check microcircuits in planar packages of the 564, 1564, 133, 533 series and others), you must use a special panel for such packages. The author's version of the device is assembled on a breadboard with installation with an M GTP wire, if desired, it will not be difficult for a radio amateur to develop a printed circuit board, taking into account the radio components and housing available to him.
The tester, assembled without errors, is easy to set up. It is only necessary to select the resistor R12 of the power protection unit. To do this, turn on the ammeter between terminals 14 and 7 of the panel and select the value of resistance R12 to achieve ammeter readings of 100 mA with an error of no more than 10 mA.
The procedure for working with the tester is clear from the description of its circuit and the given table. Chip type LP8 TTL / TTLSh series (four gated repeaters) should be checked using OR logic. To check the K155LA18, K155LL2 microcircuits in cases with eight pins (DIP-8), close the pins 11 and 14 of the panel with a jumper, set the SB1, SB2 switches to the "LAZ" position, and insert the tested microcircuits into the lower part of the panel according to the scheme (key DD5 is shown dotted line in the figure). In this case, the indication of serviceability is carried out by LEDs HL3, HL4, and LEDs HL1, HL2 blink.
It is not difficult to adapt this logic tester to test the K561KTZ microcircuit (and its analogues). To do this, the lower terminals of the resistors R13-R16 must be connected to a common wire, sections SB1.1, SB2.1 of switches SB 1, SB2 should be set to the "LE1" position, and sections SB1.2, SB2.2 - to the "LAZ »And select the reference logic function 2I.
LITERATURE
1. Shilo V. L. Popular digital microcircuits. Directory. - M .: Radio and communication, 1987.
2. Shilo V. L. Popular CMOS microcircuits. Handbook. - M .: Jaguar, 1993.
3. Pukhalskiy GI, Novoseltseva T. Ya. Designing discrete devices on integrated circuits. Handbook. - M .: Radio and communication, 1990.
4. Petrovsky I. I. and others. Logical IS KR1533, KR1554. Directory. In 2 parts. - M .: Binom, 1993.
5. Karabutov A. Tester of semiconductor devices. - Radio, 1995, No. 6, p. 28.
Journal "Radio", 1996, No. 8, p.33
This article will talk about how to check the operability of a microcircuit using a conventional multimeter. Sometimes it is quite easy to determine the cause of the malfunction, and sometimes it takes a long time, and as a result, the malfunction remains unexplained. In this case, it is necessary to replace the part.
Three options for action
Checking microcircuits is a rather complicated process, which often turns out to be impossible. The reason lies in the fact that the microcircuit contains a large number of different radioelements. However, even in such a situation, there are several ways to check:
- visual inspection. Having carefully studied each element of the microcircuit, you can find a defect (cracks on the case, burnout of contacts, etc.);
- ... Sometimes the problem lies in a short circuit on the side of the supply element, replacing it can help correct the situation;
- performance check. Most microcircuits have not one, but several outputs, therefore a malfunction of at least one of the elements leads to the failure of the entire microcircuit.
The easiest to check are the KR142 series microcircuits. They have only three pins, so when any voltage level is applied to the input, its level is checked at the output with a multimeter and a conclusion is made about the state of the microcircuit.
The next on the complexity of the check are microcircuits of the K155, K176 series, etc. To check, you need to use a block and a power source with a specific voltage level, selected for the microcircuit. As in the case of the KR142 series microcircuits, we apply a signal to the input and control its output level using a multimeter.
Application of a special tester
For more complex checks, you need to use a special microcircuit tester, which you can purchase or do yourself. When the individual units of the microcircuit are called, data will be displayed on the display screen, analyzing which you can come to a conclusion about the serviceability or malfunction of the element. It should not be forgotten that in order to fully check the microcircuit, it is necessary to completely simulate its normal operation, that is, to ensure the supply of voltage at the required level. For this, the check should be carried out on a special test board.
Often, it is impossible to check the microcircuit without unsoldering the elements, and each of them must be called separately. How to ring out the individual elements of the microcircuit after soldering will be described later.
Transistors (field and bipolar)
We transfer the multimeter to the “dialing” mode, connect the red probe to the base of the transistor, and touch the collector output with the black one. The display should show the value of the breakdown voltage. A similar level will be shown when checking the circuit between the base and emitter. To do this, connect the red probe to the base, and apply the black one to the emitter.
The next step is to check the same terminals of the transistor in reverse connection. Connect the black probe to the base, and touch the emitter and collector with the red probe in turn. If the display shows one (infinite resistance), then the transistor is good. This is how field-effect transistors are checked. Bipolar transistors are tested in a similar way, only the red and black test leads are swapped. Accordingly, the values \u200b\u200bon the multimeter will also show the opposite.
Capacitors, resistors and diodes
The serviceability of the capacitor is checked by connecting the probes of the multimeter to its terminals. Within a second, the resistance will grow from units of Ohm to infinity. If you swap the probes, the effect will be repeated.
To make sure that the resistor is working properly, it is enough to measure its resistance. If it is different from zero and less than infinity, then the resistor is good.
Checking diodes from a microcircuit is quite simple. Having measured the resistance between the anode and the cathode in direct and reverse sequence (swapping the multimeter probes), we make sure that in one case one is at the level of several tens or hundreds of Ohms, and in the other it tends to infinity (the unit in the “dialing” mode on the display ).
Inductance and thyristors
Checking the coil for an open circuit is carried out by measuring its resistance with a multimeter. The element is considered serviceable if the resistance is less than infinity. It should be noted that not all multimeters are capable of checking inductance.
The thyristor is checked as follows. We apply the red probe to the anode, and the black one to the cathode. The multimeter should display infinite resistance. After that, we connect the control electrode to the anode, observing the drop in resistance on the multimeter display to hundreds of ohms. Detach the control electrode from the anode - the thyristor resistance should not change. This is how a fully functional thyristor behaves.
Zener Diodes, Loops / Connectors
To test a zener diode, you will need a power supply, a resistor and a multimeter. We connect the resistor to the anode of the zener diode, through the power supply we apply voltage to the resistor and the cathode of the zener diode, gradually raising it. On the display of a multimeter connected to the zener diode terminals, we can observe a smooth increase in the voltage level. At a certain point, the voltage stops growing, regardless of whether we increase it with a power supply. Such a zener diode is considered serviceable.
To check the loops it is necessary. Each contact on one side should call with a contact on the other side in the "ringing" mode. If one and the same contact rings with several at once, there is a short circuit in the loop / connector. If it does not ring with any - a break.
Sometimes the malfunction of the elements can be determined visually. To do this, you will have to carefully examine the microcircuit under a magnifying glass. The presence of cracks, darkening, contact violations may indicate a breakdown.
This device is used to check microcircuits and is a better version of the device for checking ICs described in The device is designed to test almost all domestic digital integrated circuits (ICs) TTL and CMOS structures, as well as some analog keys, if they are made in a case 238.16-1 with unipolar power supply. They can check the IC series K155, K158, K131, K133, K531, K533, K555, KR1531, K176, K511, K561, K1109
The device consists of a power supply, an LED indicator, a generator, an output switch, a voltage switch, a connector for connecting external devices and two panels for ICs. The microcircuits are connected depending on the number of pins to XS1 or XS2. The pin switch allows you to apply a logical “0” or a logical “1” to any of the 16 pins of the IC, as well as when the SA20 toggle switch is on - pulses from the generator with a frequency determined by SA19.
The generator is also designed to test ICs with dynamic inputs. The XS3 connector is used to connect external devices (generator, oscilloscope), as well as to connect an additional power supply when testing the K511 series IC, +15 V must be supplied to terminals 24 and 25. The indicators display information about the state of the IC. If the indicator is on, this pin has a logical "1", and if not - a logical "0". The HL17 LED signals generator operation. The built-in power supply allows using SA18 to switch the supply voltage for different types of ICs. 
The switch SA21 ... SA25 selects the IC pin to which power is supplied. When checking analog keys K1109, the power supply is set by toggle switches SA1 ... SA16. The generator output is supplied via switch SA20.
The body of the device is soldered from foil-coated fiberglass with dimensions of 320x100x50 mm. The device uses constant resistors MLT-0.125, capacitors - KM5, KM6. Microswitches - MT-1, MT-3, TV2-1.
