Learning Activity Objectives
After studying learning activity 2, it is expected that training participants will be able to:
- Mention the symptoms of damage to each TV receiver block.
- Repairing damage to the TV set
- Answer the formative test questions correctly.
Material Description
Repairing a TV should be done carefully and thoroughly because it can have fatal consequences. Television is an electronic device that has high electrical voltage. In addition, not all damage is necessarily caused by damaged components. Sometimes it is damaged due to poor soldering so that the component legs are not perfectly connected to the PCB. Symptoms and causes of TV damage vary. Symptoms that arise can be total death, no sound or poor picture production. Meanwhile, TV damage can also be caused by components that have been eaten or imperfect connections between components.
TV is totally dead
There are several damages that can cause the TV to not work at all. In general, this kind of damage occurs in the power supply or horizontal deflection circuit.
A.1 Is the TV completely dead and the indicator light off?
Cause: most likely damage to the power supply circuit.
Solution: check the power grid, input to output regulator circuit. Pay attention to the following regulator circuit schematic. In general, TV power supplies have a voltage output of 115 V, 24 V and 5 V, depending on the TV brand. Replace damaged components and repair imperfect circuit paths. The arrows indicate components that are easily damaged.
A.2 Is there a creaking sound from the switching transformer?
Cause: usually the output voltage is blocked because there is a damaged component.
Solution: Remove the load from the regulator output by removing the base leg of the horizontal transistor or one of the legs of the horizontal transformer and measure the output voltage. If the regulator output shows a voltage that matches the instructions on the PCB, check the entire voltage distribution path from the regulator output and the entire horizontal circuit.
Figure 19. Measuring Regulator Output
Pay attention to the following horizontal circuit schematic diagram. In general, the components that are easily damaged are the flyback transformer, horizontal transistor and capacitor (see arrow).
A.3 Is the indicator light on but no picture or sound appears?
Figure 21. TV is off, indicator light is ON
Cause: possible damage to the horizontal circuit or regulator. The voltage produced by the regulator is usually blocked because the voltage limiting diode is damaged. Not all TV brands have this diode. The diodes used usually have the serial numbers R2M and R2KY.
Solution: on some TVs there are usually 2 colors of indicator light. When the TV is turned on the red indicator, after a few seconds it changes to green or turns off and the TV show can be enjoyed. If the indicator remains the same color or changes but only for a moment, it means there is protection. Check the output voltage from the regulator to the load. If this voltage is not normal, it means the regulator circuit is disturbed or there is a component that is damaged and needs to be replaced.
A.4 No Raster But Good Sound
Figure 22. No Raster But Good Sound
Figure 23. High Voltage Circuit Region
Cause: video amplifier circuit, high voltage limiter or CRT is damaged.
Solution: Is the high voltage connected to the CRT normal? If normal, check the high voltage of the CRT cathode. If the measured voltage is absent, check the high voltage circuit. Is the high voltage to the CRT cathode normal? If normal, check the video amplifier circuit. If all is normal, check the CRT circuit. The damage that often occurs is that the filament is broken so that the CRT does not emit light.
Figure 24. Picture Tube (CRT)
A.5 Dark Images
The raster does not light up brightly even though the screen flyback position is at maximum.
Figure 25. Dark Image Screen
Cause: The CRT anode voltage is too low due to damage to the high voltage circuit, horizontal deflection circuit or power supply circuit. The voltage of all CRT cathodes becomes large due to interference in the video amplifier.
Solution: Is the output regulator voltage normal? If normal, check the CRT cathode voltage. If abnormal, check the output regulator voltage. Is the CRT cathode voltage normal? If normal, check the CRT anode voltage. If abnormal, check the high voltage circuit.
A.1.6 Horizontal Single Line Raster
Figure 26. One Horizontal Line Raster
Cause: The source of the interference depends on the oscillator the TV uses.
Solution: Check the vertical deflection circuit Check all IC or transistor electrodes with a multitester.
Figure 27. ICs and Transistors That Are Easily Damaged
B.1 Poor Horizontal Synchronization
Black stripes cannot be removed from the raster even though synchronization has been set.
Figure 28. Poor Horizontal Sync
Cause: This type of damage is rare in new TVs. If damage does occur, it is usually caused by components that are already old.
Solution: Check the horizontal oscillator circuit. There is a possibility that the elko is dry. Usually indicated by the back of the elko that looks dull or cracked.
B.2 Part of the Image is Shifted Horizontally / Vertically
Figure 29. Part of the Image is Shifted Horizontally
Figure 30. Part of the Image is Shifted Vertically
Cause: The resulting video signal is mixed with the synchronization signal input on the AFC circuit.
Solution: Check for dry elko or leaking diodes in the synchronization circuit, video buffer circuit and AGC.
B.3 Bad Vertical Sync
Figure 31. Bad Vertical Sync
Cause: The damage is located in the integrator circuit or in the vertical oscillator circuit. This type of damage usually occurs on old TVs.
Solution: Check the vertical oscillator circuit. The vertical regulator of the old TV may be worn out, while on the new TV the damage occurs due to a leaking ceramic capacitor.
B.4 Poor Vertical and Horizontal Synchronization
Cause: Most damage occurs in the synchronization signal separator and in the synchronization signal amplifier circuit, or sometimes occurs in the AGC circuit and noise canceler circuit.
Solution: Are the vertical and horizontal synchronization weak? If yes, check the synchronization signal separation circuit. If the synchronization signal separation circuit is normal, check the synchronization signal amplifier section. If the synchronization signal amplifier section is normal, check the AGC circuit and noise elimination circuit.
C.1 Narrow Image
Figure 32. Narrowed Screen Image
Cause: This type of damage is rare in new TVs. The horizontal output voltage is lower, so the sawtooth current circuit in the horizontal deflection coil (yoke) becomes weaker.
Solution: Check the output voltage of the power supply. If the output voltage is lower, check the components. Check the horizontal deflection circuit especially the transistors in it. Check the condition of the yoke, if damaged or burned it must be replaced.
Figure 33. Horizontal Deflection Transistor
C.2 Horizontal Widening
Figure 34. Horizontal Widening
Cause: This kind of damage is caused by a damaged Vr.
Solution: Check the components. If the power supply voltage is normal, check the CRT anode voltage. If the CRT anode voltage is too low, check the circuit. Change the VR value, if there is no change, replace the VR. Check the power supply output voltage. If the output voltage is greater, high voltage amplifier.
C.3 Image Height Reduction
Figure 35. Insufficient Image Height
Cause: The amplitude of the sawtooth wave in the vertical deflection coil is too small so that the output of the vertical deflection circuit is insufficient.
Solution: Check V SIZE and V LIN. On digital TV, the setting can be done by setting the remote control on the adjustment menu. If there is no change, check R and Tr in the vertical deflection circuit. The red arrows are the R and Tr in the damaged vertical deflection circuit.
Figure 36. Vertical Deflection Circuit
C.4 Top or Bottom Shrinkage
Figure 37. Shrinkage of Top or Bottom
Cause: Caused by an inappropriate Vr value or a dry electrolytic condenser.
Solution: Set VR, if there is no change then VR is damaged. Check the elko whether it is still good or dry.
C.5 Longitudinal Vertical Image
Figure 38. Vertical Too Large
Cause: The sawtooth current in the vertical deflection coil is too low.
Solution: Adjust the VR, if there is no change, maybe the elko is dry.
D.1 Snow Noise In Images
Snow Noise On Image
Cause: Field intensity at the low frequency signal reception location. TV antenna system is damaged. High frequency amplifier circuit is damaged.
Solution: Rotate the antenna until a good picture is obtained. Fix the antenna cable path. Check the soldering on the tuner and AGC blocks.
D.2 Low Image Contrast
Figure 40. Low Image Contrast
Cause: The damage is located between the mixer circuit and the video amplifier.
Solution: Check for resistors whose values have increased or are shorted.
D.3 Slash Line Appears
Figure 41. A diagonal line appears in the image
Cause: Usually interference from the radio transmitter.
Solution: Move the antenna and TV away from sources of interference frequencies.
D.4 White Spot Noise
Figure 42. White Dot Noise
Cause: Interference from the spark plugs of the motorbike, car or high voltage electrical distribution wires.
Solution: Keep the antenna and TV away from high voltage power lines. Use a coaxial cable for the TV antenna.
D.5 Black Horizontal Line
Figure 43. Horizontal Lines in the Image
Cause: Usually caused by tools that use small motors.
Solution: Move the TV away from the noise source.
D.6 There are shadows from other channels
Figure 44. Image Interrupted by Other Channels
Cause: Cross modulation occurs by a channel that has a large transmit power.
Solution: Adjust the height of the TV antenna, adjust the Vr value on the AGC circuit.
D.7 Color Disorders
TV images appear blue, red, yellow, cyan or green.
Color Disorders
Cause: Usually damage occurs due to interference in the RGB or CRT circuit.
Solution: Check the RGB matrix circuit, usually there is an enlarged resistor value or bad soldering. If there are no damaged components, adjust the RGB VR. If still no results, check the CRT.
Step 1 Troubleshooting CRT
Remove the CRT legs of the red green blue section by desoldering. If there is no information on the CRT legs of red, green, blue, then look for three resistors on the RGB matrix that have the same shape, size, and color. Remove the legs of the three resistors and then turn on the TV power.
Step 2 Troubleshooting CRT
Attach the negative multimeter probe to ground and the positive to the CRT legs or to the solder marks of each resistor leg one by one. If when the multimeter probe is attached and the TV screen displays each bright base color, it means the CRT is still in good condition. However, if the base color that appears is dim or does not appear at all, the CRT is damaged and needs to be replaced.
E.1 No Sound/Weak Sound
Figure 51. Sound Circuit
Cause: There is damage to the audio and speaker circuit.
Solution: Touch the input of the audio amplifier circuit with your finger. If you hear hissing in the speaker, check the audio IF section. If not, check the audio amplifier circuit section or check the speaker.
F. Summary Table of Alleged Damage
| GEJALA KERUSAKAN | DUGAAN KERUSAKAN |
|--------------------------------------------|-------------------------------------------------------------------------------|
| Tidak ada suara dan tidak ada raster | Catu Daya, Defleksi Horisontal. |
| Tidak ada gambar maupun suara | Penguat Video, IF Video dan HF |
| Gambar baik tetapi tidak ada suara | IF Audio, Detektor Video dan Penguat Audio. |
| Sinkronisasi lemah (tipis) | Sinkronisasi, AGC, AFC dan Osilator |
| Tidak ada raster | Defleksi Horizontal, Tegangan Tinggi, Tabung Gambar, Fokus dan Penguat Video. |
| Gambar monokromatis | Pembangkit Sinyal Kroma dan Tabung Gambar. |
| Tidak ada warna | Penguat Band Pass, ACC, Pemati Warna, Osilator 4,43 MHz dan Gerbang Burst. |
| Sinkronisasi warna lemah | Osilator 4,43 MHz, Gerbang Burst dan Detektor Fasa. |
| Tidak ada warna merah, hijau ataupun biru. | Demodulasi Warna |
| Pergeseran warna | Rangkaian RGB dan Rangkaian Konvergen. |TV Repair Formative Test
SESSION 1
- The color signal is fed to the color splitter circuit through the chrominance amplifier circuit.
- The color splitter outputs signals each containing a red color difference signal and a blue color difference signal. These signals are fed to the demodulator V and demodulator U.
- Demodulator on a 4.43 MHz carrier signal in correct phase.
- Color suppressor suppresses Color enhancer When there is no incoming chrominance signal
- Signal V is a signal that has been weakened, namely the red color difference signal. What is meant by signal U is the blue color difference signal. Meanwhile, signal Y is the luminance (brightness) signal.
- Damage to the power supply stabilizer circuit will result in unstable images and faulty sound.
- The image is in the form of a single horizontal straight line, the damage is located in the vertical circuit, while the damage to 1 vertical line is located in the horizontal circuit.
- The extra high voltage produced by the flyback transformer for the purposes of the picture tube anode is 10 to 30 KV DC.
- A shaking image with a rattling sound is often caused by damage to the capacitor in the video IF filter transformer.
- The image is not linear (people become tall) caused by the vertical return coupling system (the elco is damaged).
SESSION 2
Question 1:
Write four effective steps of TV repair procedure!
Answer 1:
The four effective steps of TV repair procedure are;
- It is well known that the damage is caused
- Estimate the damaged blocks based on the fault state.
- Divide the damaged block and find the damaged area
- Find and replace damaged components.
Question 2:
Which components are easily damaged by heat during soldering?
Answer 2:
Components that are easily damaged by heat during soldering are transistors and ICs.
Question 3:
Explain the difference between voltage testing and resistance testing!
Answer 3:
The difference between voltage testing and resistance testing is
- Voltage testing is the measurement of the output voltage of the transistor/IC when the TV is ON.
- Resistance testing is measuring the resistance of a component to see if it is broken or short-circuited when the TV is OFF.
Question 4:
Name the equipment for TV repair!
Answer 4:
The equipment for TV repair is
- Multimeter
- Solder
- Desoldering
- Screwdriver
- Pliers
- Tweezers
- Paintbrush
Question 5:
To make it easier to find damage, in addition to measuring tools are:
Answer 5:
To make it easier to find damage, in addition to measuring tools, there is a TV circuit diagram.
SESSION 3
Question 1:
Explain the differences between the NTSC, PAL and SECAM systems in TV signal reception!
Answer 1:
The differences between the NTSC, PAL and SECAM systems in TV signal reception are;
- NTSC: Superior in terms of compatibility but requires color type settings due to high color distortion.
- PAL: Lower compatibility but does not require complex color type settings.
- SECAM: Lowest compatibility, but does not require synchronization or color type.
Question 2:
Mention the three main functions of a TV receiver!
Answer 2:
The three main functions of a TV receiver are;
- Amplifies the sound carrier signal, detects the signal and feeds it to the sound amplifier.
- Amplifies the image carrier signal, detects the signal and feeds it to the picture tube.
- Generating a sawtooth current to deflect the electron beam in the picture tube, while also producing extra high voltage for the needs of the picture tube anode.
Question 3:
Write six subsections on the color series block!
Answer 3:
Six subsections of the color series block;
- Chrominance Amplifier
- Color Synchronization
- Automatic Color Control
- Color Killer
- 180° phase sequence
- Demodulation.
Question 4:
Draw the primary color circle (R, G, B)!
Answer 4:
The primary color circle (R, G, B) is;
Question 5:
It is known: At the TV transmitter station there is a scene that is viewed from left to right consisting of green, red and blue lines. The camera outputs a voltage of 1 Volt, when it sees color.
Question: How does the luminance signal behave during the tracking process?
Answer 5:
The behavior of the luminance signal during the tracking process is The voltage output by the camera is as follows;
| -------- | Kamera H | Kamera M | Kamera B | Kamera Y |
|------------------------------------|----------|----------|----------|----------------------|
| Garis Hijau Garis Merah Garis Biru | 1V 0 0 | 0 1V 0 | 0 0 1V | 0,59 V 0,30 V 0,11 V |Question 6:
The TV receiver receives information consisting of Y = 0.8 V; M = 1V; B = 0.5 V. What is the voltage H?
Answer 6:
The TV receiver captures information consisting of Y = 0.8 V; M = 1V; B = 0.5 V. The voltage H is The graph is the image below:
- Y = 0.3 M + 0.59 H + 0.11 B
- 0.8 = (0.3 x 1) + (0.59 x H) + (0.11 x 0.5)
- 0.8 = 0.3 + 0.59 H + 0.055
- 0.59 H = 0.8 -- 0.355
- H = 0.455/ 0.59 = 0.75 V
TV Signal Information
Question 7:
Mention 4 types of damage to the Video Amplifier circuit!
Answer 7:
The four types of damage to the Video Amplifier circuit are:
- No raster
- The raster is there but the image is weak
- Image is too black
- The image is too contrasty.
Question 8:
What is the extra high voltage on a flyback transformer?
Answer 8:
The extra high voltage on the flyback transformer is 10 to 30 KV.
Question 9:
Explain the 4 efficiency steps required in a repair procedure!
Answer 9:
The four efficiency steps required in a repair procedure are:
- The state of the damage disturbance is well known
- Estimated corrupted blocks based on corruption disturbances
- Divide the damaged block and find the damaged area
- Find and replace damaged components.
Question 10:
Explain how to check whether the components below are good or damaged:
- a) Diode
- b) Elco
- c) Transistor
- d) Transformer
Answer 10:
How to check whether the components below are good or damaged is:
- Diode. Both multimeter probes are touched to each leg of the diode, then touch the opposite. If it produces 1 time the needle moves and 1 time it does not move, it means the diode is good and vice versa.
- Elco. If the needle moves then returns to its original position, it means the elco is good. If the needle does not return, it means it is leaking, the needle does not move at all, it means it is damaged.
- Transistor. Probe -- on the base, probe + on the emitter and collector. The needle does not move well and vice versa is damaged. Probe + on the base, probe -- on the emitter and collector. The needle moves well and if the needle does not move it is damaged.
- Transformer. Connect each multimeter probe to the primary part then the secondary part is good if the needle moves. Now check if there is a short circuit between the primary and secondary with the iron core. If the needle does not move, it means it is good.
TV Fault Finding Procedure
The efficiency steps required in the repair procedure are as follows.
- Known Fault Condition When receiving a TV to be serviced, listen/ask the customer about the damage to make it easier to check.
- Estimated Damaged Blocks The TV is turned on, adjust the volume, contrast, brightness and color control buttons. Look at the symptoms that appear on the TV screen to guess which part is damaged. Make an estimate of the damaged block according to the damage table.
- Splitting a Corrupted Block Although the suspicious sequence has been determined, the examined area is very large. Therefore, the damaged part is more efficient to be found if the examined area is more limited.
- Finding the Damaged Part After making the suspected area narrower, measure the voltage and resistance using a Multitester.
Create a REPAIR REPORT
After the repair or component replacement is complete, a report needs to be made in the form of a service checklist and repair history card (History Card).
TV Service Report
- TV Brand: .......................................
- Size : .......................................
| | | | | |
|----------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----|-------|-------------------|
| NO | GEJALA KERUSAKAN | YA | TIDAK | BAGIAN YANG RUSAK |
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 | TVMatiTotal Terdengar Suara Desis Getaran TV Mati, Indikator Menyala Suara Baik, Raster Tidak Ada Gambar Gelap Raster 1 Garis Horisontal Sinkronisasi Horisontal Jelek Gambar Tergeser Horisontal Gambar Tergeser Vertikal Sinronisasi Vertikal Jelek Gambar Kurang Tinggi Gambar Terlalu Tinggi Penyusutan Gambar Atas Dan Bawah Gambar Jelek Kontras Gambar Rendah Muncul Garis Miring Gangguan Warna Gangguan Suara | | | |Repair History Card
| NO | TGL. | GANGGUAN KERUSAKAN | KOMPONEN YANG DIGANTI | PARAF |
|---------------------|------|--------------------|-----------------------|-------|
| 1 2 3 | | | | |Summary
- There are four efficiency steps required in the repair procedure, namely: Know the exact damage disturbance. Estimate the damaged block based on the disturbance condition. Divide the damaged block and find the damaged area. Find the damaged component.
- Transistor and IC components are easily damaged by heat, so soldering must be done quickly.
- When soldering TV components, the TV's power cable must be unplugged from the power outlet.
- Replaced components must be of the same standard.
- Troubleshooting will be more effective if the TV circuit schematic is available.
Bibliography
- Indrawan 1985, Black and White Transistor TV Service/Repair Techniques, Bintang Terang Servis Publisher.
- PT. Bukaka Teknik Utama 1988, Practical Instructions for BW TV Trainer Model IB 3611.
- PT. Bukaka Teknik Utama 1988, Practical Instructions for Color TV Trainer Model CE -- 140 F.
- S. Reka Rio, Ir and Yoshikatsu Sawamura 2002, Color Television Repair Techniques, PT. Pradnya Paramita Jakarta.
- Sofyan 2005, Finding & Repairing Color TV, Kawan Pustaka Publishers.
- Wasito S 1982, TV Techniques, Theory and Servicing, Karya Utama Publisher, Jakarta.
- Wasito S 1986, Color TV Techniques, Theory and Servicing, Karya Utama Publisher, Jakarta.
Accurate Measurement of Electronic Components
At some point it is necessary to measure accurately or precisely the data of a component or device, and it is necessary to understand the general principles involved. For good accuracy (± 0.1%) the bridge method is used to compare the unknown with the standard. The Wheatstone bridge arrangement (figure 3.13) can be used for resistance measurement and is in a state of equilibrium when Ra/Rb = Rx/Rs. The detector indication D is minimum. This is because the voltage drop at the ends of Rb is the same as the voltage drop at Rs. The balance point (its balance is not, depending on the value of the supply voltage and any sensitive zero indicator can be used. Its accuracy depends on the tolerance and stability of the comparison resistors Ra, Rb and the standard resistor Rs. In a state of equilibrium, when Ra and Rb have been set at zero indication. Ra/Rb = Rx/Rs.
It means that;
Figure 3.13 Wheatstone Bridge
In the universal and commercial RCL bridge, three bridge circuits are used (figure 3.14). The power supply frequency for the bridge is usually 1 kHz, and a very sensitive ac detector is usually used an amplifier tuned to 1 kHz with its output supplying a moving coil meter through a rectifier. In the balanced state, the component values are expressed in digital form for easy reading.
Figure 3.14: AC circuit for L, C, R
Figure 3.14: AC circuit for L, C, R
Figure 3.14: AC circuit for L, C, R
For a specific example of a general purpose bridge is:
Apart from bridges which are not often needed in service situations, there are some good and fast methods for measuring components. Two things to note:
- The effect of each measurement current or measurement voltage on the component, if the measurement current is too high it will cause too much power dissipation in the device being measured or a test voltage will cause breakdown damage (burst).
- Sources of errors in measurement are errors such as meter inaccuracy and loading effects, connecting wire inductance, connecting wire capacitance, connecting wire resistance. In general, test leads should be as short as possible, especially if low values are measured, and even more so if the measurement is carried out at high frequencies. Equipment sold on the market to measure capacitance and inductance is also accurate even though it must be done manually, as can be seen in Figure 3.15.
Figure 3.15 Capacitance or Inductance Meter
1. Measurement of Active Components
For various discrete semiconductors the most important parameters are given in table 3.5.
Table 3.5 Important Parameters of Discrete Semiconductors
A simple diode test to check whether the VF and V(BR) values are within their upper limits can be done using a constant current source. In almost all measurements of this type, the current must be kept constant to avoid excessive heat and possible damage to the components. A diode characteristic of 5 mA, for example, is performed on a diode and the VF is read with a Voltmeter and it turns out to be off.
Figure 3.16 Characteristics of Semiconductor Diodes
If IF/VF characteristics are required, a circuit can be used to demonstrate them, on an oscilloscope and must use a ramp generator, as shown in Figure 3.17.
Figure 3.17 RAMP Circuit for TEST Circuit, and Using CRO to Demonstrate Forward Direction Diode Characteristics
Figure 3.17 RAMP Circuit for TEST Circuit, and Using CRO to Demonstrate Forward Direction Diode Characteristics
Semiconductor breakdown voltage should always be measured with a constant current source. In the breakdown state, which is generally an "avalanche effect", a rapid increase in current occurs when the voltage rises. A "Break down" pentest circuit in Figure 3.18 can be used without damaging the diode, namely for V(BR), VZ, V(BR)CEO and so on.
The circuit is actually a constant current generator produced by the Q1 circuit. The base of Q1 is maintained at 5.6 V by a zener diode, so VE is approximately 5 V. The emitter current and collector current can be adjusted by varying the emitter resistance RV1.
GC Loveday,1980,64
Figure 3.18 Reverse Direction Diode Transmissive Tester Circuit and Various Diodes
The current will be fairly constant throughout the collector voltage changes from 10V to 200V. Note that the maximum current is about 1 mA, which is low enough to cause no damage. If a component is tested for its breakdown limit, the test switch is pressed and the voltage at the ends of the component will rise to its breakdown value where the current is limited. The voltage at the ends of the device under test can be read with a multimeter. This reverse breakdown diode test can be done for all types of diodes available, from rectifier diodes, LEDs and zener diodes as shown in the picture. Only a DC power supply with adjustable voltage must be provided and the minimum available voltage is 250 Volts DC.
In terms of physical form, transistors have various forms. Figure 3.19 shows the forms of transistors that are often found on the market.
Figure 3.19 Various Forms of Transistors - Klaus Tkotz, 2006
Transistors operate normally when the emitter and base are given forward voltage, while the collector and emitter are given reverse voltage. In a simple circuit it is described as follows:
Figure 3.20 Normal Working Voltage of NPN and PNP Transistors
The hFE tester is generally used as an indicator of transistor operation and a simple circuit to measure it is shown in figure 3.21. Note that hFE is a large dc signal gain "Common emitter or grounded emitter:
At certain values of VCE and IC. Various circuits can be built to measure precisely, for example hFE, hfe or other h parameters, but it is a question.
It might be better, if we create the characteristic curve using for example an "XY plotter" to automatically generate the curve (figure 3.22).
VCE(sat) is usually specified with IC/IB = 10 : 1, So to switch the transistors a go/no-go pentest circuit as in Figure 3.23 can easily be made and the VCE(sat) values at certain IC values measured with a digital voltmeter.
Figure 3.22 Using an XY Plotter to Obtain Transistor Characteristics.
Figure 3.23 VCE(sat) measurement
- IC = 10 mA note below RB : RC = 10 : 1
- VCE(sat) measurements on IC values are obtained by varying the RB and RC values.
- For FETs, the parameters can be re-verified.
The circuit for checking the above values is shown in Figure 3.24. For Yfs (also called gm) transconductance, the circuit has a fixed bias level set so that an operating point can be established. Then VGS is varied by the signal from the ac source and the resulting change in drain current is recorded. The value of Yfs will be 2 milliSiemens.
Figure 3.24 FET measurement
Finally for the discrete component thyristor shown a pentest circuit in figure 3.25. This circuit can check the correctness of the FET operation by pairing special values of IGT and VGT to the gate of the thyristor. Initially R2 is set to minimum, S1 is closed the meter current I should be low (50u A) and the voltmeter should show 24 V. This is because the thyristor blocks the forward direction, so it is nonconducting. M1 should show about 100 mA, and M2 shows about 1 V. Then as R2 is increased the current value gradually decreases until a point of nonconduction of the thyristor is reached. The current shown just before nonconduction is the holding current IH.
Figure 3.25: Circuit for Testing Thyristors
2. Test on linear and digital ICs
Testing linear and digital ICs can also be done carefully on all parameters, but more generally indicating circuit function is needed. In other words, does an op-amp have gain or does a counter IC divide properly? By mounting the IC in a "TEST JIG" that requires the IC to oscillate or perform a logic function, good devices can be saved and separated from bad or defective ones. This procedure can also be used to test individual active devices such as transistors, unijunctions and thyristors.
transistor, unijunction and thyristor
Figure 3.26 Various forms of linear and digital ICs
Two examples of this method are shown in Figure 3.27. The first shows how a linear IC of the DIP type, 8 pins can be checked by functional inspection. The components around the IC will form a low frequency oscillator (2 Hz). If the IC is inserted into the "test jig" socket correctly, the LED will flash on and off. A CMOS Quad 2 input positive (I/p) NAND gates (4011B) can also be checked by connecting components around the socket (14 pins) so that low frequency oscillation occurs. Additional inspection of the internal gates can be done by operating the two "Inhibit switches" Sl and S2.
Figure 3.27 Example of IC Test Circuit a) OP-AMP IC Test Circuit (b) CMOS NAND CD 4011 test circuit
3. Optical Electronic Components
One thing that is very interesting for you in studying electronic components is to study optical electronic components, better known as optoelectronics. Why is that? Because all optoelectronic components are always related to light, whether the component works because there is light, or produces light or changes light.
Well, as a reminder, let's start from the definition first, that optoelectronic components are components that are affected by light (optoelectric), light-emitting components and components that affect or change light.
Optoelectric components can be categorized as:
- Photo emission: here the radiation that hits the cathode causes electrons to be emitted from the surface of the cathode, for example: photomultiplier tube, LED (Light Emitting Diode), LCD (Liquid Crystal Dynamic) and laser diode (Light Amplification by Stimulated Emission of Radiation)
- Photo conductive: here when the component is illuminated the resistance of the material changes, for example: photo diode (given reverse voltage) and LDR.
- Photovoltaic: this component will generate a voltage at the output that is proportional to the radiation strength, for example: photo diode (without being given voltage), solar cell, photo transistor, photo darlington, photo FET and opto electronic coupler.
All types of photo emission usually produce light, fluorescence (become bright) to produce very strong light that can weld metal. In LED will produce light of various colors depending on the type of semiconductor used and this component has a long life and strong so that currently widely used as a replacement for brake lights on cars or motorcycles. While the development of LCD is very rapid and widely used as a replacement for computer monitor or TV tube screens. In laser light is also widely used in medicine, precision measurements in industry and others.
For conductive photos, this component will have a very large resistance (above 100 K Ohm) when not illuminated and only a few hundred ohms when illuminated, usually used in automatic garden lights. Try as an assignment: create / find an automatic garden circuit using LDR where when dusk begins, the lights in the garden or on the terrace of the house start to turn on automatically. Explain how the circuit works why it can be so.
For photovoltaic components will produce voltage / current when exposed to light, the most widely used today is solar cells used as voltage generators for battery charging as a substitute for power sources when the AC power goes out. Try to find out about it.
Analysis of the Working Principle of a TV Tuner (Tuner)
By adopting the tuner model in a television circuit, students are expected to be able to understand and describe the working principles of a tuner circuit.
Tools and materials:
- TV
- Related Tv Schematic Diagram.
- AVO meter
Basically, the tuner consists of an RF amplifier circuit, OSC.Local and Mixer which work at the following frequencies:
- Band 1 ---------->> 47 - 68 Mhz (VHF-L)
- Band 2 ---------->> 174 - 223 Mhz (VHF-H)
- Band 4/5 -------->> 470 - 854 Mhz (VHF)
The tuning circuit is placed in a tightly closed metal box, to provide optimal protection from external electromagnetic induction interference.
Work Procedure (SOP):
- Prepare equipment and practice materials
- Turn on the TV and turn on the channels as shown in the table.
- Measure the voltage at the tuning pins, record the results.
- Turn off the TV, and return it to its original place.
And the following are the results we obtained:
| Titik Ukur Pin | Besar Tegangan Pin Pada Saat Menala |
|----------------|-------------------------------------|--------|----------|------|---------|
| | TVRI | TRANS7 | INDOSIAR | SCTV | METROTV |
| VL | 4.6 | 4.6 | 4.6 | 4.6 | 4.6 |
| VH | 4.6 | 4.6 | 4.6 | 4.6 | 4.6 |
| VT | 0.9 | 6.6 | 2.4 | 3.7 | 5.6 |
| BM | 4.8 | 4.8 | 4.8 | 4.8 | 4.8 |
| IF | 0 | 0 | 0 | 0 | 0 |
| AGC | 2.2 | 4.7 | 4.7 | 4.7 | 4.7 |
| CLK (ACR) | 0 | 0 | 0 | 0 | 0 |
| SCL | 4.7 | 4.7 | 4.7 | 4.7 | 4.7 |
| SDA (DATA) | 4.7 | 4.7 | 4.7 | 4.7 | 4.7 |
| HB | 4.8 | 4.8 | 4.8 | 4.8 | 4.8 |
| LB | 4.8 | 4.8 | 4.8 | 4.8 | 4.8 |
| ST (33V) | 34 | 34 | 34 | 34 | 34 |
| | | | | | |
| | GLOBALTV | RCTI | ANTV | TPI | TRANSTV |
| VL | 4.6 | 4.6 | 4.6 | 4.6 | 4.6 |
| VH | 4.6 | 4.6 | 4.6 | 4.6 | 4.6 |
| VT | 4.2 | 3.2 | 4.2 | 1.9 | 1.9 |
| BM | 4.8 | 4.8 | 4.8 | 4.8 | 4.8 |
| IF | 0 | 0 | 0 | 0 | 0 |
| AGC | 4.7 | 4.7 | 4.7 | 4.7 | 4.7 |
| CLK (ACR) | 0 | 0 | 0 | 0 | 0 |
| SCL | 4.7 | 4.7 | 4.7 | 4.7 | 4.7 |
| SDA (DATA) | 4.7 | 4.7 | 4.7 | 4.7 | 4.7 |
| HB | 4.8 | 4.8 | 4.8 | 4.8 | 4.8 |
| LB | 4.8 | 4.8 | 4.8 | 4.8 | 4.8 |
| ST (33V) | 34 | 34 | 34 | 34 | 34 |Symptoms & Related Tuner Malfunctions
| Gejala | Kerusakan |
|-----------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------|
| Tidak ada suara, tidak ada raster | Rangkaian Daya, Rangkaian Defleksi Hor. |
| Tidak ada gambar maupun suara | OSC Lokal |
| Suara baik tapi tidak ada gambar | Penguat Video, Rangkaian IF Video, Rangkaian HF |
| Gambar baik tapi tidak ada suara | Rangkaian Audio IF, Defleksi Audio, Penguat Audio |
| Sync. lemah atau tipis | Rangkaian Sync. AGC, AFC, OSC, Vertikal |
| Raster garis horizontal | Rangkaian Defleksi Vertikal |
| Tidak ada raster | Rangkaian Defleksi HOR, Rangkaian Tegangan Tinggi, Rangkaian Tabung Gb, Penguat Audio, Rangkaian ABL, Rangkaian Focus. |
| Gambar tidak fokus | Rangkaian Pemfocus, Rangkaian Pembangkit Tegangan Tinggi, Tabung Gb. |
| Gambar monochromatis | Rangkaian Pembangkit Signal Kroma, Rangkaian Tabung Gb. |
| Tidak ada warna dalam gambar | Penguat Band Pass, Rangkaian AGC, Pemati Warna, OSC 4.43 MHz |
| Sync. warna dalam gambar lembah | OSC 4.43 MHz, Rangkaian Tabung Burs, Penguat Burs, Detector Pasa |
| Tidak ada warna merah, hijau maupun biru dari pada gambar | Rangkaian Demodulasi Warna, Penguat Demodulasi Warna |
| Pergeseran warna pada gambar | Rangkaian Konvergen. |Tuner Troubleshooting Flow Chart
Summary
- To reduce the possibility of a component being damaged, we must understand the limitations of each component.
- Failure of fixed and variable resistors can occur gradually and change their value to be large or suddenly break due to incorrect use, but fixed resistors have a very low failure rate (very reliable) compared to variable resistors and other components.
- Failure of a capacitor can be open or short circuit and each type may have different possible causes.
- In semiconductor components, the failure rate is quite high, especially during fabrication, because there are many processes that must be carried out which are quite complicated.
- Failure of semiconductor components can be open or short circuit, and these components are more sensitive when compared to passive components, so they must be handled more carefully.
- Prevention so that components do not get damaged quickly when used needs to be known and paid attention to, so that the components do not get damaged before being used.
- Components also need to be tested to ensure their existence, whether they can still be used or not. Testing can be done simply or more accurately by using a simple circuit that we can assemble ourselves.
- Optical electronic components are components that are affected by light (optoelectric), light-emitting components and components that affect or change light. Consisting of three categories, namely: photo emission, photo conduction and photo voltaic.
Chapter 3 practice questions
- Why do we need to understand the limitations of a component? Give an example!
- Mention the failures that can occur in fixed resistors, and what causes them!
- Explain why partial failure can occur in a potentiometer!
- Mention the causes of damage, both open and short circuits, to the electrolytic capacitors that we often use!
- Briefly mention the causes of failure in semiconductors during fabrication!
- What needs to be done to prevent damage when we are handling components, especially semiconductor components!
- Mention the important things that we need to do when handling MOS components!
- Component testing is divided into three main areas, name them!
- Make a circuit that can demonstrate the characteristics of a forward-direction diode! Briefly explain how it works!
Group task
Try designing the task below in groups (maximum 3 people):
- Make a TEST JIG circuit for an Op-Amp IC, and explain briefly how it works!
- Once your group is confident with the design, you can implement it during the practical lesson with the help of the practical instructor.