Sembilan akal sehat PCB pemeriksaan

1. Dilarang keras menggunakan peralatan uji yang diarde untuk menyentuh TV langsung, audio, video, dan peralatan pelat bawah lainnya untuk menguji papan PCB tanpa transformator isolasi.

Dilarang keras menguji TV, audio, video, dan peralatan lainnya secara langsung tanpa transformator isolasi daya dengan instrumen dan peralatan dengan penutup yang diarde.

Although the general radio cassette recorder has a power transformer, when you come into contact with more special TV or audio equipment, especially the output power or the nature of the power supply used, you must first find out whether the chassis of the machine is charged, otherwise it will be very easy The TV, audio and other equipment that are charged with the backplane cause a short circuit of the power supply, which affects the integrated circuit, causing further expansion of the fault.

2. Pay attention to the insulation performance of the electric soldering iron when testing the PCB board

It is not allowed to use a soldering iron for soldering with power. Make sure that the soldering iron is not charged. It is best to ground the shell of the soldering iron. Be more careful with the MOS circuit. It is safer to use a low voltage soldering iron of 6~8V.

3. Before testing the PCB board, understand the working principle of integrated circuits and related circuits

Before inspecting and repairing the integrated circuit, you must first be familiar with the function of the integrated circuit used, the internal circuit, the main electrical parameters, the role of each pin, and the normal voltage of the pin, the waveform and the working principle of the circuit composed of peripheral components.

Jika kondisi di atas terpenuhi, analisis dan pemeriksaan akan jauh lebih mudah.

4. Do not cause short circuit between pins when testing the PCB board

Saat mengukur tegangan atau menguji bentuk gelombang dengan probe osiloskop, jangan menyebabkan korsleting antara pin sirkuit terpadu karena geser dari kabel uji atau probe. Yang terbaik adalah mengukur pada sirkuit cetak periferal yang terhubung langsung ke pin.

Any momentary short circuit can easily damage the integrated circuit. You must be more careful when testing flat-package CMOS integrated circuits.

5. Resistansi internal instrumen uji papan PCB harus besar

When measuring the DC voltage of the IC pins, a multimeter with the internal resistance of the meter head greater than 20KΩ/V should be used, otherwise there will be a large measurement error for the voltage of some pins.

6. Pay attention to the heat dissipation of the power integrated circuit when detecting the PCB board

Sirkuit terpadu daya harus memiliki pembuangan panas yang baik, dan tidak boleh bekerja dalam kondisi daya tinggi tanpa pendingin.

7. The lead wire of the PCB board should be tested reasonably

If you need to add external components to replace the damaged parts of the integrated circuit, small components should be selected, and the wiring should be reasonable to avoid unnecessary parasitic coupling, especially the grounding between the audio power amplifier integrated circuit and the preamplifier circuit end.

8. To inspect the PCB board to ensure the welding quality

When soldering, the solder is firm, and the accumulation of solder and pores are likely to cause false soldering. The soldering time is generally no more than 3 seconds, and the power of the soldering iron should be about 25W with internal heating.

The integrated circuit that has been soldered should be carefully checked. It is best to use an ohmmeter to measure whether there is a short circuit between the pins, confirm that there is no solder adhesion, and then turn on the power.

9. Do not easily determine the damage of the integrated circuit when testing the PCB board

Do not judge that the integrated circuit is damaged easily. Because the vast majority of integrated circuits are directly coupled, once a circuit is abnormal, it may cause multiple voltage changes, and these changes are not necessarily caused by damage to the integrated circuit.

Selain itu, dalam beberapa kasus, ketika tegangan terukur dari setiap pin cocok atau mendekati nilai normal, mungkin tidak selalu menunjukkan bahwa sirkuit terpadu baik. Karena forum elektronik EDA365 menemukan bahwa beberapa kesalahan lunak tidak akan menyebabkan perubahan tegangan DC.

Metode debugging papan PCB

Untuk papan PCB baru yang baru saja diambil kembali, Forum Elektronik EDA365 merekomendasikan agar Anda mengamati terlebih dahulu apakah ada masalah pada papan, seperti apakah ada keretakan yang jelas, korsleting, sirkuit terbuka, dll. Jika perlu, periksa apakah hambatan antara catu daya dan kabel ground cukup besar.

For a newly designed circuit board, debugging often encounters some difficulties, especially when the board is relatively large and there are many components, it is often impossible to start. But if you master a set of reasonable debugging methods, debugging will get twice the result with half the effort.

PCB board debugging steps:

1. For the new PCB board that has just been taken back, we must first roughly observe whether there are any problems on the board, such as whether there are obvious cracks, short circuits, open circuits, etc. If necessary, check whether the resistance between the power supply and the ground wire is large enough.

2. Kemudian komponen dipasang. Modul independen, jika Anda tidak yakin bahwa mereka berfungsi dengan baik, yang terbaik adalah tidak menginstal semuanya, tetapi menginstal bagian demi bagian (untuk sirkuit yang relatif kecil, Anda dapat menginstal semuanya sekaligus), sehingga mudah untuk menentukan rentang kesalahan. Hindari kesulitan memulai ketika Anda menghadapi masalah.

Generally speaking, you can install the power supply first, and then power on to check whether the output voltage of the power supply is normal. If you do not have much confidence when powering up (even if you are sure, it is recommended that you add a fuse, just in case), consider using an adjustable regulated power supply with current limiting function.

Preset arus proteksi arus lebih terlebih dahulu, kemudian perlahan-lahan naikkan nilai tegangan catu daya yang diatur, dan pantau arus input, tegangan input, dan tegangan output. Jika tidak ada perlindungan arus lebih dan masalah lain selama penyesuaian ke atas, dan tegangan output telah mencapai normal, catu daya baik-baik saja. Jika tidak, putuskan catu daya, temukan titik kesalahan, dan ulangi langkah di atas hingga catu daya normal.

3. Next, install other modules gradually. After each module is installed, power on and test it. When powering on, follow the above steps to avoid over-current and burn out components due to design errors or/and installation errors.

Finding the method of PCB board failure

1. Temukan papan PCB yang rusak dengan mengukur metode tegangan

Hal pertama yang harus dipastikan adalah apakah tegangan pin catu daya dari setiap chip normal, dan kemudian periksa apakah berbagai tegangan referensi normal. Selain itu, forum elektronik EDA365 mengingatkan: juga mengkonfirmasi apakah tegangan kerja setiap titik normal, dll.

For example, when a general silicon transistor is turned on, the BE junction voltage is about 0.7V, while the CE junction voltage is about 0.3V or less. If the BE junction voltage of a transistor is greater than 0.7V (except for special transistors, such as Darlington, etc.), it may be that the BE junction is open.

2. Signal injection method to find faulty PCB board

Add the signal source to the input terminal, and then measure the waveform of each point in turn to see if it is normal to find the fault point. Sometimes we also use simpler methods, such as holding a tweezers with our hands, and touching the input terminals of all levels to see if the output terminals respond. This is often used in amplifying circuits such as audio and video (but note that the hot bottom plate This method cannot be used for circuits with high voltage or high voltage circuits, otherwise it may cause electric shock).

Jika tidak ada respon pada level sebelumnya, tetapi ada respon pada level berikutnya, berarti masalahnya terletak pada level sebelumnya dan harus diperiksa.

3. Other ways to find faulty PCB boards

Ada banyak cara lain untuk menemukan titik kesalahan, seperti menonton, mendengarkan, mencium, menyentuh, dll.

“Seeing” is to see if there is any obvious mechanical damage to the component, such as cracking, burning, deformation, etc.;

“Listening” means listening to whether the working sound is normal, for example, something that shouldn’t be ringing is ringing, the place that should be ringing is not ringing or the sound is abnormal, etc.;

“Bau” adalah untuk memeriksa apakah ada bau yang aneh, seperti bau terbakar, bau elektrolit kapasitor, dll. Untuk personel perawatan elektronik yang berpengalaman, mereka sangat sensitif terhadap bau ini;

“Menyentuh” ​​adalah untuk menguji apakah suhu perangkat normal dengan tangan, misalnya, terlalu panas atau terlalu dingin.

Some power devices will heat up when they work. If they are cold to the touch, it can basically be judged that they are not working. But if the place that shouldn’t be hot is hot or the place that should be hot is too hot, that won’t work either.

For general power transistors, voltage regulator chips, etc., it is completely fine to work below 70 degrees. What is the concept of 70 degrees? If you press your hand up, you can hold it for more than three seconds, it means that the temperature is below 70 degrees (note that you must touch it tentatively first, and don’t burn your hands).