If you understand the components and their limitations well, this is an important part of finding electronic circuit damage. For example: knowing that it is generally very unlikely that a resistor of any type will have a short circuit, so if there is a suspicion of a short circuit there is no need to check the resistors in the circuit. Another aspect that needs to be considered is that many component damages are caused by user errors (by the person), an estimated 40% of damage due to misuse is usually caused when operating components beyond the capabilities of the component or poor handling of the component.
1. Fixed Resistor
Different types of fixed resistors include:
The picture can be seen in Figure 3.1. The types of metal-film, metal oxide, or cermet (metal glaze) are widely chosen in use, because these types have good stability, both in storage and in operating conditions. Note that resistors with tolerances of 5, 10, or 20% are color-coded with two significant bands, followed by a number of bands (or decimal places) and a tolerance band (see Table 3.1).
There are also resistor values and tolerances printed on the resistor body sometimes stated directly, for example 1.82k 1% (1820 ohms ± 1%) or in code form such as 1821 F.
Figure 3.1: Types of Fixed Resistors
Values above 100 ohms are indicated by three digits followed by a fourth digit indicating the number of zeros that follow. For values below 100 ohms the letter R indicates the decimal point with all significant digits. After the value code, a letter is added to indicate the tolerance:
F = ±1%, G = ±2%, J = ±5%, K = ±10%, M = ±20%
For example:
- R 33 M = 0.33 ohm ± 20%
- 4701 F = 4700 ohms ± 1%
- 6804 M = 6.8 M ohm ± 20%
- 2202 K = 22000 ohms ± 10%
Table 3.1: Significance of Common Resistor Color Numbers
| Warna | Pengali | Toleransi | | Singkatan | | |
|--------|----------|-------------------|-------------------|-----------|-------------|----------------|
| | | Resistor | | | | |
| | | MIL resistor (±)% | EIA resistor (±)% | | | |
| | | | | MIL- STD | EIA 3 huruf | EIA alternatif |
| | Resistor | | | | | |
| HITAM | 1 | 20 | | BLK | Blk | BK |
| COKLAT | 10 | 1 | 1 | BRN | Brn | BR |
| MERAH | 102 | 2 | 2 | RED | Red | R,RD |
| ORANGE | 103 | | | ORN | Orn | O,OR |
| KUNING | 104 | | | YEL | Yel | Y |
| HIJAU | 105 | | 0,5 | GRN | Grn | GN,G |
| BIRU | 106 | | 0,25 | BLU | Blu | BL |
| UNGU | 107 | | 0,1 | VIO | Vio | V |
| ABUABU | | | 0,05 | GY | Gra | GY |
| PUTIH | | | | WHT | Wht | WH,W |
| EMAS | 10-1 | 5 | 5 | (a) | Gld | |
| PERAK | 10-2 | 10 | 10 | SIL | Sil | |The resistor installation and calculations are:
2. Failures in Fixed Resistors
Every resistor when operating will dissipate its power. The temperature increase caused by the dissipated power will be maximum in the middle of the resistor body, this is called "Hot spot temperature". It must be emphasized here, that resistors generally show a low failure rate or the resistor is very reliable. Failures and their causes are listed in table 3.2.
Table 3.2: Failures of Fixed Resistors
| Tipe Resistor | Kegagalan | Kemungkinan Penyebab |
|------------------------------------------------------------------------------|---------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| Komposisi karbon | Berubah membesar Sirkit terputus | ● Perubahan karbon atau zat pengikat di bawah pengaruh panas, tegangan atau kelembaban. ● Penyerapan udara lembab menyebabkan pembengkak- an, dan menjadikan pertikelpartikel karbon untuk memisahkan diri . ● Panas berlebih membakar tengah-tengah resistor. ● Tekanan-tekanan mekanik menyebabkan retak-retak pada resistor. ● Kap-kap ujungnya terlepas karena montase yang buruk pada papan. ● Kawat putus karena pembengkokan yang berulang- ulang.` |
| Resistor-resistor film.(karbon, oksida logam,film logam, metal glase) | Sirkit terputus | ● Film terkelupas karena temperatur tinggi atau tegangan tinggi. ● Lapisan film tergores atau terkikis ketika di fabrikasi. ● Pada nilai-nilai resistansi yang tinggi (lebih besar 1 mega ohm) spiral resistan sinyal harus tipis dan karenanya kegagalan sirkit terbuka lebih besar kemungkinannya. ● Kontak-kontak ujungnya buruk. Biasanya disebabkan oleh tekanan mekanik karena montase yang jelek pada sirkit. |
| Wire wound (resistor kawat) | Sirkit terputus | ● Keretakan kawat, terutama bila digunakan kawat kecil , karena ketidakmurnian menyebabkan keretakan. ● Perkaratan kawat yang dise babkan oleh elektrolitis yang ditimbulkan oleh udara lembab yang terserap. ● Kegagalan sambungan-sambungan yang dilas. |3. Variable Resistor (Potentiometer)
Potentiometers can be grouped into three main groups depending on the resistive material used, namely:
- Compound carbon, carbon poured in the form of a solid path or layer of carbon plus filler. poured on a substrate or base.
- A roll of Nichrome wire or other resistance wire rolled into an insulating form usually in the form of a small pipe.
- Cermet is a thick film layer on a ceramic substrate or base. There are two types of potentiometers commonly sold, namely: type A whose resistance changes are logarithmic when rotated and type B whose resistance changes are linear when rotated.
Figure 3.2 Basic Potentiometer Construction
In general, potentiometer requirements fall into three categories:
- Preset or trimmer (figure 3.3.a)
- General usability controls (figure 3.3.b)
- Precision control
Examples with their requirements are given in Table 3.3.
Figure 3.3. Potentiometer Shape
Table 3.3: Variable Resistor Applications
| Tipe | Contoh Aplikasi | Tole ran si | Kelini eran | Stabi litas | Putaran yang diharap kan | Gulung an |
|-------------------------------------------|-----------------------------------------------------------------------|-------------|-------------|---------------|--------------------------|---------------------|
| Preset atau Trimmer | pengaturan lebar pulsa yang tetap dari mono stabil | ± 20% | Tak penting | Tinggi ±2% | Kurang dari 50 | Tunggal atau banyak |
| Kontrol kegunaan umum (pasang pada panel) | Kontrol kecemerlangan pada osiloskop | ± 20% | ±10% | Medium ±10% | 10.000 | Tunggal |
| Kontrol kepresisian (pasang pada panel) | Tegangan Output yang terkalibrasi dari sebuah catu daya laboratorium | ±3% | ±0.5% | Tinggi ± 0.5% | 50.000 | Tunggal atau banyak |4. Failures in Variable Resistors
The failure rate is higher than that of fixed resistors, for potentiometers a failure rate of approximately 3 x 10-6 per hour is common, but these figures vary depending on the method used by the manufacturer. The damage to a potentiometer can be partial or total.
Partial damage:
- Increasing contact resistance causes an increase in electrical noise.
- Intermittent contact, this can be caused by dust particles, grease (lubricant) or abrasive materials that accumulate between the sliding contact and the track. This disturbance can be removed with a cleaning agent such as contact cleaner.
Total damage:
- It is an open circuit between the path and its end connections or between the sliding contact and the path.
- This can be caused by rusting of metal parts due to moisture, or swelling of metals/plastics that occurs during high temperature casting of the line.
5. Capacitor
A capacitor consists of two conducting plates separated by a dielectric insulator. The well-known formula for capacitance C is:
With:
- ε0 is the absolute permittivity
- εr is the dielectric constant
- A is the area of the plate (m2)
- d is the distance between the plates, i.e. the dielectric thickness (m).
The plate area, dielectric constant must be high, and the dielectric thickness small to obtain a large enough C. The efficiency of a capacitor is determined by the total electric charge (Q=CV) that can be stored.
The types of capacitors can be seen in Figure 3.4. On the top row are electrolytic capacitors including polar types (having + and - poles), while the second row is plastic film capacitors and the third row is ceramic capacitors. Both are non-polar capacitors (their installation is free because they have no poles). The price of a capacitor is read on the capacitor body.
Figure 3.4: Types of Fixed and Variable Capacitors
Remember the calculation formula for C series and C parallel is the opposite of the formula for resistors (see page 3-2).
6. Failure of Capacitor
Capacitors are reliable components, showing low failure rates especially when derated (see Chapter 2.3.7). Capacitor life can be extended by:
- Operated below the permissible voltage limit.
- Operated at low ambient temperatures, reducing the temperature by 10ºC can double its lifespan.
Possible damage:
Catastrophic (sudden & total):
- Short circuit: dielectric breakdown
- Open circuit: damage to the end connector.
Degradation (gradual and partial):
- The decrease in resistance of the insulation or the increase in leakage current in the electrolyte type is gradual.
- The increase in series resistance, which is an increase in the dissipation factor.
Some causes of damage are:
- Damage during fabrication; chloride contamination of the electrolyte, will cause rusting of internal connections, mechanical damage to the ends of metal-clad capacitors, causing overheating and open circuits.
- Wrong use; The capacitor is used beyond the rated voltage, or poor assembly techniques cause mechanical stress on the end connectors and casing (Seal).
- Environment; Mechanical shocks, mechanical vibrations, high/low temperatures, and humidity.
A list of faults and possible causes for several types of capacitors is shown in table 3.3.
Table 3.3: Capacitor Damage and Its Causes
| JENIS C | KERUSAKAN | KEMUNGKIN PENYEBABNYA |
|----------------------|-----------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------|
| Kertas | Kering bahan renda man, menimbulkan sambung singkat Sirkuit terbuka. | Kebocoran seal. Kejutan mekanik, termal atau perubahan-perubahan tekanan. Kejutan mekanik / thermal. |
| Keramik | Sambung singkat Sirkuit terbuka Perubahan-perubah an kapasitansi | Pecahnya dielektrika karena kejutan atau getaran Pecahnya sambungan Elektroda perak tidak melekat benar pada perak |
| Film plastik | Sirkuit terbuka | Kerusakan pada semprotan diujung, ketika fabrikasi atau asembeling. |
| Alumunium Elektrolit | Sambung singkat, karena bocor. Kapasitansi mengecil. Sirkuit terbuka | Hilangnya dielektrika. Temperatur tinggi. Hilangnya elektrolit karena tekanan, kejutan mekanik atau temperatur. Pecahnya sambungan internal. |
| Mika | Sambung singkat Sirkuit terbuka. | Perpindahan perak disebabkan oleh kelembaban yang tinggi. Perak tidak menempel ke mika. |7. Semiconductor Devices
Semiconductor classification:
Mechanical Damage
- Diffusion processes
- Metallization Process
- Mechanical Process.
Incorrect Usage:
- Exceeding its maximum supply voltage, current and power
- Inserting/removing the IC while the voltage is on.
Environmental Hazards
- Electrical interference
- Voltage shock by machine or relay
- Magnetic field.
8. Damage to Semiconductors
These two semiconductors are easily damaged if subjected to excessive load.
Possible damage that occurs is:
- Short circuit: at junction BE, BC or CE.
- Open: at junction BE or BC.
Some causes of semiconductor damage are:
9. Precautions When Handling and Testing Components
Bending connecting wire:
- Don't do it repeatedly
- Do not get too close to the component body (3-5 mm).
Mechanical Shock
- The fall of semiconductor components
- Cutting the connecting wire
- Scraping the surface of the component.
Thermal shock
- Soldering Iron 20-50 Watt
- Maximum soldering temperature 300°- 400°C
- Soldering time 5 seconds
- Use a "Solder Wick" or "Attractor" to remove components using solder.
Electrostatic shock (also on MOS)
- Use a small probe test
- Final MOS component installation
- The soldering iron tip must be free of voltage.
- Do not insert/remove semiconductor components while the power supply is on.
- Avoid shock voltage from the relay or when the switch is on.
- No signal is attached to the input when the power supply is off.
- Use anti-static wristband/clothing (at the factory) when installing MOS IC (figure 3.5).
10. Test Circuit for Components
Verification (re-verification):
- Measuring resistors using an Ohmmeter.
- Checking whether a saturated transistor becomes non-conductive if the base-emitter junction is shorted.
Test Go or No-go:
Determining whether some parameters or characteristics of a component are within specification limits.
Relatively accurate measurements of component parameters:
Usually done in laboratories to test the durability of a component that will be used in a new product to be launched. In order to really produce a circuit / equipment that is in accordance with what is expected. Almost all parameters / characteristics of the components are tested here.
Note: Typically in test and service equipment, the goal is to find faults quickly, and therefore the first and second methods are used more often than the third.
11. Simple Component Testing
Tests to determine a short circuit or open circuit, use the ohm function on a multimeter, but to check for an open circuit it is necessary to unsolder one end of the component connecting wire and lift it from the hole and then measure it, otherwise, components connected in parallel with the suspected component will give incorrect resistance measurement results.
Another alternative used to check for an open circuit resistor is to bridge the suspected resistor with a known resistor and then check the circuit resistance again. Leaking capacitors can also be tested using an ohmmeter, again by disconnecting one end of the capacitor from the circuit. An electrolytic capacitor should exhibit low resistance initially, as it charges, but its resistance should quickly return to infinity.
A broken capacitor or open circuit can be determined by installing another capacitor in parallel and checking the circuit in operating condition, or removing the capacitor and testing it on a simple pentest setup as shown in Figure 3.6 using a 1 kHz audio generator and two meters.
In this case Cx = ½ πfVo with an accuracy of ±10% for capacitive values 1000pF to 1 uF.
Figure 3.6. Simple circuit
A better way is to use an ac bridge as in Figure 3.7 to compare the unknown capacitor with a standard capacitor.
Figure 3.7. Capacitance bridge (zero indicator can be an oscoscope or sensitive ac meter)
At equilibrium the following applies: C1 = (R2/R1) C2
Testing diodes, transistors and other semiconductors can also be done using the ohm function of a multimeter. The important thing is to know the polarity of the battery in the meter, in a particular meter the common terminal (marked in black) has a positive voltage on the ohm function.
If you do not know the battery connection in the meter you are using, you can determine the polarity by connecting another multimeter to the voltage function, or by measuring the forward or reverse resistance of a semiconductor, diode or transistor of known polarity see figure 3.8. Once you have determined the polarity of the ohmmeter, you can measure / determine many things about the transistor.
Figure 3.8: Using a semiconductor diode to determine the polarity of a multimeter on the ohm function. The meter shows low resistance, meaning that its black terminal is connected to the positive terminal of the battery inside.
The steps to test a transistor using a multimeter (Ohmmeter) are:
Figure 3.9: Measuring the junction resistance of an npn transistor using a multimeter. Forward bias on the base-miter, should show low resistance. Usually less than 1 k ohm.
Figure 3.10: Forward bias at the collector base should show low resistance (less than 1 k ohm)
Figure 3.11: Reverse bias on the base emitter should show high resistance (greater than 100 k ohms)
Figure 3.12: The reverse bias on the base collector should show high resistance (greater than 100 k ohms)
When testing components, and it is carried out on transistors, FETs and ICs, then it should:
REMEMBER!
- Check the power supply close to the actual components, and for ICs directly at the respective pins.
- Do not use a large test probe, because a test probe that is too large can easily cause a short circuit. Avoid excessive heat when unsoldering components and do not remove it when the unit is on.
- Never remove or insert the device without first turning off the power supply.
- Components can be easily damaged due to excessive current shock.
How to Test Active Components
The tests that will be carried out here are mostly tests when there is working voltage (on a circuit), so that if there is damage to a circuit, there is no rush to unsolder a component but measurements can be taken first to be sure.
Diode
- The forward voltage of silicon, germanium, Schottky, Tunel, and Zener diodes should not exceed 1.1V (in series). However, if it exceeds this value, it indicates an open diode, which must be removed, tested, and replaced.
- If a diode is conducting current but the diode voltage drop is zero or only a few millivolts, the diode is shorted. Remove, test, and replace.
- A short-circuited rectifier diode can damage other diodes, filter capacitors, and power transformers, so they must be checked before providing power supply.
Transistor
- Transistors that exhibit a forward base-emitter voltage of more than 1.1V (base positive for NPN,
- negative base for PNP) has an open base-emitter junction and must be replaced.
- Transistors that have passed the testing stage can be decided that the transistor is in good condition. The testing method is as follows:
Figure 2.56(a): A short circuit between base and emitter causes the collector voltage to rise and equal VCC and VRC to drop to zero, unless the transistor is normally biased at cut off.
Figure 2.56(b): If the collector load has a resistance close to zero, current drops across the emitter resistor. A short circuit between BE causes VRE to drop, unless the transistor is normally biased at cutoff.
Figure 2.56(c): If two transistors are in parallel, both must be turned off to observe the decrease in VRC.
Figure 2.56(d): If the transistor is unbiased and VC = VCC, a resistor is added from VCC to the base to turn the transistor on. Calculate R to ensure that IB < 1 mA for small signals and IB < 100 mA for power transistors. Adding R causes VC to drop.
Figure 2.56(e): If the base is controlled directly by the transistor, it is necessary to turn off Q1 before Q2 can be tested by method (a) or (d).
Figure 2.56(f): In an active transistor circuit, the collector signal is inverse of the base signal even though it is distorted. If the collector voltage decreases when the base voltage increases, and vice versa, the transistor is essentially functioning.
Meanwhile, testing transistors without bias can be seen in CHAPTER 4.
FET
FET damage is often indicated by an abnormal gate voltage. Gate triggering is determined from a simple resistive network and the expected voltage can be calculated, because for a good FET it has IG = 0 (gate current = 0), as shown in Figure 2.57. Do not forget the effect of the load on the meter. A large deviation from the desired VG indicates that the gate current is flowing. If the FET is an insulated-gate FET, it means that the FET is damaged. This happens if the connection on the FET is damaged, or is given a forward trigger on the gatesource. Check the VGS voltage of 0.6V.
- Phase difference test can be used Figure 2.56 (f).
- Junction FETs can be tested out of circuit with an ohmmeter between gate and source (small R in one polarity and large R in the opposite). By shorting gate-source, a resistance of several hundred ohms is found between drain-source, either polarity.
- Insulated-gate FETs can be checked for substrate-source and for gate-source resistance. The drain-source (gate-to-source) resistance should be in the range of a few hundred ohms for depletion types and infinity for enhancement types.
SCR
An ON SCR should show a voltage of 0.1V to 1.5V between its anode and cathode or when the anode-cathode conduction is positive. The SCR is short-circuited when the voltage approaches zero.
VGK should never be above +1.2V when there is working voltage. If it does, it means the gate is broken open.
The occurrence of a short circuit between the gate-cathode causes the SCR to remain triggered, passing a positive voltage from the anode-cathode as in Figure 2.58. If a positive voltage does not appear when given a sine signal between the anode and cathode, it means the load is open or the SCR is short-circuited.
With an Ohmmeter the SCR should show a connection like a diode between the cathode-gate (one polarity has small resistance and vice versa), and a very large resistance (open) for both anode-cathode polarities. See figure 2.59.
With an Ohmmeter, the following can also be done: the Ohmmeter polarity + to the SCR anode and the other to the cathode shows a very large value, then in this condition, briefly connect the plug on the anode (without removing it from the anode) to the gate, then the Ohmmeter reading will be small (several tens of Ohms).
UJT
It usually fails because the emitter voltage cannot reach the firing level or because the charging circuit is delivering too much current for the UJT to withstand.
It is better to unsolder the emitter leg and measure VC as shown in figure 2.60. If the voltage is not more than 0.85VB2 check the charging circuit and C. Next, connect the millimeter from C to B1. If the current exceeds the UJT valley current specification, then the charging circuit provides a lot of current, so the UJT is on.
Figure 2.60: Oscillator circuit as a UJT tester.
Diagnosis with Computer Programs
Computer diagnostic programs are used to test all parts of a computer and help determine which hardware or software is faulty. This self-test program can be used only if some essential parts of the computer such as the power supply, CPU, bus and memory device (disc) that holds the test program are operating properly.
All computers are equipped with a number of programs. Some of them are required in the system and are called operating systems. Some of the operating systems serve for maintenance, such as resetting registers, clearing temporary memory, and doing general tracking of computer operations.
Nowadays, there are many computer programs to diagnose damage, both software program damage and physical damage to computers and components, for example programs to check TTL ICs, transistors, printers and so on.
It should be noted that this diagnostic can be used if most of the computer elements are functioning properly.
The CPU must receive proper power supply, its clock and timing systems must be working and the buses must be functioning properly. If any of these basic components are not working, then this diagnostic program cannot be used.
And if this happens, then you need to use a simple way as explained in the previous section (the first 6 ways). Besides that, you still always need a damage tracking manual from the factory.