Inspection methods for various components in power supplies

There are many components in the power supply, so do you know how to inspect it? This article mainly explains how to inspect each electronic component in the switching power supply, various inspection standards and inspection methods, come and get it !

1. Resistance

1) Visual inspection, the incoming material packaging should be intact and undamaged, and the labels should be clear;

2) The color of the color ring is clear and easy to identify. The color of the color ring is consistent with the nominal resistance value. The pins are not oxidized or blackened; the numbers are correctly marked.

3) The resistance value is consistent with the color ring mark.

4) The resistor is not broken and the coating layer is peeled off;

5) There should be no oil stains, water stains or other dirt on the surface. Dust caused by transport materials and capable of being blown away by air is acceptable.

6) Use a multimeter to measure the resistance.

7) Use a 30W or 40W soldering iron to tin the resistor pins. The solder should be able to completely cover the pins to be qualified.

2. Capacitor

1. First determine whether the specifications, capacity, error, pressure resistance value, temperature resistance value and error value required by the BOM are consistent with the incoming materials.

2. The actual measured value of capacitance (measured with LCR METER) must be within the standard value ± error range.

3. The spacing between the capacitor pins must be consistent with the technical data requirements.

4. The capacitor's trademark must be clear and complete, the paint must be bright, there must be no pollution, and the appearance must be intact.

5. The lead-tin alloy plating layer in the lead-out pin of the capacitor should be bright and consistent in color and should not show signs of oxidation such as spots.

6. The distance between the capacitor pins should be less than 1MM, and the ribbon arrangement must be neat and uniform without any unevenness.

7. Check whether the measured capacity (plug-in capacitance) is within the error range, and determine whether the type and specifications are correct.

A. Electrolytic capacitors have experienced skin peeling off and wrong packaging after wave soldering (4.7UF/16V, the wrong packaging is 47UF/16V). The specifications of the polyester capacitors are at the wrong foot spacing, and the wrong specifications lead to excessive volume. assembly,

B. Common plug-in capacitors include electrolytic capacitors, ceramic capacitors, metal film capacitors, safety capacitors, polyester capacitors, and monolithic capacitors. The focus of checking plug-in capacitors is their type and specifications. Determine which one should be used before inspection. , and then measure the specifications (including volume and foot distance) as required and try out the installation if possible.

8. Measure the diameter and height with a caliper based on the BOM.

9. Refer to the BOM and measure the forward withstand voltage of the single-use regulated power supply according to the withstand value.

10. Use a capacitance testing instrument to measure its capacity.

11. The positive and negative polarity markings of the capacitor cannot be reversed, and the marked capacity must be consistent with the actual capacity. Chip capacitors:

12. Check the appearance and pay attention to whether there is oxidation or damage.

13. Use a capacitance meter to measure whether the capacity is within the error range.

14. For customers with special requirements, such as Kangchuang, they should also pay attention to whether the color and shape are different or different from last time. If there are any differences, they should promptly notify the customer before use after confirmation, and notify relevant personnel to follow up.

A. When inspecting chip capacitors, special attention should be paid to the color and shape (volume, thickness). If several colors and shapes are found in the same incoming material, or if they are inconsistent with the last incoming material, a written notice must be submitted immediately. Contact the customer in the form and confirm it before use. If there is a difference in color or shape between each incoming material and the last incoming material, a sample must be kept for next time comparison and to facilitate production and inspection. Check whether the electrodes of the capacitor are damaged. If there are errors, specifications, and withstand voltage values ​​in the incoming materials that are different from the BOM, contact the customer immediately if found.

B. Never be careless when purchasing self-purchased chip capacitors. Before inspection, ask the same type and customer, find the corresponding BOM, and sample. Carefully check the mark on the tray to see if it is consistent with the BOM or the incoming materials provided by the customer, and then observe carefully. Whether the shape (volume, thickness) and color are consistent with the sample, if it is not certain, report it to the quality control section chief and relevant units for confirmation, and keep the sample.

C. The film content of different customers cannot be misappropriated. Be especially careful when confirming the film content for the production department. You must inquire and investigate thoroughly before drawing a conclusion.

D. If two capacities appear in a PCB board at the same time, but the errors are different, targeted records should be kept and samples should be kept for tracking.

E. Record the brand of the chip capacitor to understand its performance.

F. When inspecting tantalum chip capacitors, please note that the side with silk screen is the positive electrode. There are four common tantalum capacitor specifications:

Types A, B, C, and D. Type A is the smallest in size; Two tantalum capacitors with the same capacity, what are the special requirements for tantalum capacitors, example: RS0404A-UK

The 100UF/16V LOW ESR on the control board means low impedance and should be yellow. Qingde tantalum capacitors were mistaken for ordinary capacitors and the model was incorrect.

G. Representative symbols on the material tray:

CC41 1805 CG 102 K 500 TN

Type Specification Material Capacity Error Pressure Resistance Value Packaging Terminal Material

H. The materials of chip capacitors are divided into: NPO (good), X7R (general), Y5V (poor).

3. Inductance

1. Appearance: The surface is not dirty or damaged, the inductance mark is complete and clear, the model and specifications are correct, and the lead pins are not oxidized, bent, or deformed.

(Visual inspection method)

2. Structural size: The main body size and lead pin size of the inductor should meet the assembly or sample requirements.

(Try it on or measure with a vernier caliper.)

3. Bending resistance of plug-in inductor pins: After resisting bending, the lead pins will not loosen or fall off.

(Fold the lead pin 900 degrees from the root of the lead pin, back and forth five times in total.)

4. Electrical performance: Inductance, impedance, and quality factors meet the requirements of the product specification.

(measured with LCR tester)

5. Solderability: After the solderability test, the tin surface on the tin-immersed part of the lead pin should be above 98%.

(Dip the inductor lead pins in tin for 3-5 seconds and then take them out (the temperature of the tin furnace is 245±5℃))

4. Diode

1) Appearance inspection

1. Whether the main body is damaged, cracked or deformed.

2. Are the pins oxidized, rusty, or falling off?

3. Is the printing blurry or falling off?

4. Are the positive and negative markings correct?

2) Function detection

Functional testing of ordinary diodes

1 Detection of forward voltage drop of ordinary diodes

Insert the diode under test into the circuit in series, adjust the voltage of the adjustable voltage regulator so that the current value displayed by the ammeter meets the specification requirements. At this time, the voltage displayed by the voltmeter is the forward voltage drop of the diode, or use a digital multimeter to Directly test the diode position of the forward voltage detection circuit, and the displayed value should be within the required range.

Such as IN4148 germanium tube

The forward voltage drop is generally 0.1~0.3V

silicon tube

The forward voltage drop is generally 0.5~0.7V

Detection of reverse current of ordinary diodes

Insert the diode under test into the circuit in series, adjust the voltage of the adjustable voltage regulator so that the voltage value displayed by the voltmeter meets the specification requirements. At this time, the current value displayed by the ammeter is the reverse current of the diode.

Functional test of Zener diode

Detection of Zener diode voltage stabilization.

Insert the diode under test into the line in series and adjust the adjustable regulated power supply voltage so that the current displayed by the ammeter meets the specification requirements. At this time, the voltage displayed by the voltmeter is the regulated voltage of the diode.

Detection of reverse current of Zener diode (same as detection of reverse current of ordinary diodes)

3) Solder test

Use a 30W soldering iron to test the soldering of the pins. The soldering should be good within 3 seconds.

5. Transistor

Inspection items and technical requirements

1 Appearance: The surface is not damaged, the specifications and models are clearly marked, there is no mixed material, and the pins are not oxidized.

(Visual inspection method)

2 Structural dimensions: Each structural dimension should comply with assembly or sample requirements.

(Try it on or measure with a vernier caliper.)

3. Bending resistance of the plug-in transistor lead pins: After resisting bending, the pins will not loosen or break.

(Fold the lead pin 900 degrees from the root of the lead pin, back and forth five times in total.)

4 Electrical performance: test Vbes parameters, Vces parameters, BVceo parameters, hFE parameters

5 Solderability: After soldering, the tinned surface is required to be greater than 98%

(Dip the inductor lead pins in tin for 3-5 seconds and then take them out (the temperature of the tin furnace is 245±5℃))

6. MOS tube

structure

1. Check the structural dimensions and specifications of the MOS tube according to the sample, and there should be no dimensional deviation or specification non-compliance that affects the assembly;

2. The connection between the pins and the tube body is reliable, and there should be no looseness or fall-off. There should be no looseness or fall-off when the pin welding joint is bent more than 5 times;

3. The PIN pin of the MOS tube meets the product design requirements;

4. Trial installation: When trying to install the MOS tube and the corresponding PCB board, there must be no failure to insert it in place.

performance

1. Dip the MOS tube pins into a tin furnace at 235°C and add tin for 2-3 seconds. The solder can completely wrap the pins. There must be no pins that are not tinned or tinned below 80%;

2. On-machine test: Install the MOS tube on the test lamp board, turn on the power to light the lamp, the power of the lamp meets the design requirements, the temperature of the lamp will not rise suddenly, and it will not flicker above 80V. After cooling at room temperature, it cannot There are explosions and other phenomena.

3. MOS tube measurement:

Electrical performance (Vbes/Vces/BVceo/HEF) parameters must meet the requirements of the corresponding specification or approval letter

MOS tube: Vgs(V), Rds(on), Id(mA), Vdss parameters must meet the requirements of the corresponding approval letter.

4. The amplification factor of the transistor should comply with the requirements of the specification or approval letter

Exterior

1. The surface of the MOS tube should be smooth and clean, and there should be no cracks in the heat dissipation aluminum flakes, detachment of pins or deformation;

2. The MOS tube must not be dirty;

3. The corresponding specifications and parameters printed on the MOS tube are consistent with the confirmation sample, and there must be no errors;

4. The MOS tube pins should be smooth and clean, and should not be oxidized or blackened.

Package

1. The MOS tube components are packed in tubes or trays and put into cartons to ensure that they will not be stressed during transportation and storage.

broken foot;

2. The carton markings are correct and clear.

7. Power IC

Package

1: There is no label on the packaging, and the outer label is inconsistent with the actual product.

2: The packaging box is damaged and seriously dirty, and the packaging is poor.

3: Mixed installation of different models and specifications

Visual inspection

1: IC surface is clean and free of dirt

2: IC screen printing fonts are clear and not blurry

3: The IC pins are bright and there is no oxidation on the surface.

4: The IC body is not damaged or broken.

5: There is no bending or deformation of IC pins.

6: Whether the IC silk screen font and packaging form meet the requirements of the specification

7: There is no short circuit on the IC pins, and the pin lengths are consistent.

Dimensions

1: The length, width and height of the IC body comply with the specifications.

2: IC pin length, width, height and spacing meet the specifications.

Solderability

1: The surface of the IC pin should be bright after being tinned.

1: The surface of the IC pin should be bright after being tinned.

Performance: Installation test and aging

8. Transformer

Focus on backlash

1. Whether the primary inductance meets the requirements?

2. Primary to secondary turns ratio, primary to feedback turns ratio

3. The smaller the capacitance between the primary and secondary, the primary feedback capacitance, and the secondary feedback capacitance, the better, generally only a few dozen P

4. Coupling degree: Primary and secondary coupling coefficient, coupling coefficient between primary feedback, the larger the value of the tester, the better.

5. Phase

6. Withstand voltage, primary and secondary voltage withstand, primary feedback withstand voltage, all coils withstand magnetic voltage

7. Leakage inductance

8. Appearance

9. Solderability

10. Transformer label

11. Whether the magnetic core and bobbin meet the requirements, especially if the bobbin has high requirements.

The above tests require the use of a transformer comprehensive tester and a withstand voltage meter.

How to test the coupling degree, withstand voltage and primary and secondary capacitance, and what are the criteria for evaluation?

Transformer comprehensive tester, the bigger the coupling reading, the better, the maximum is 100%. I think the transformer cannot reach this value, it is generally above 80% and below 90%.

Withstand voltage: It depends on the standards of each manufacturer. Generally, the primary and secondary 3750VAC set current is 3mA for 1 minute. No breakdown, no flashover, and no excessive abnormal noise.

Inter-turn capacitance: The smaller the better (for flyback transformer)

Replenish

For multi-winding transformers, sometimes it is also necessary to consider the issue of micro-short turns between turns on the same side, for example:

1. Defects in enameled wire production (pinhole phenomenon);

2. Products whose enameled wires are damaged during the production and processing of various coil products.

The thickness of the enameled wire is different, and the test voltage settings are also different;

9. Safety capacitors

Appearance: Inspect the appearance for damage, deformation, oxidation and other defects. The markings must be clear and correct, and whether the whole body meets the plug-in requirements. (The safety model must have a registered brand before it can be recognized) (Visual inspection)

Dimensions: Measure the dimensions of each part according to the specifications and must meet the actual assembly requirements.

Capacitance: After placing it in a room temperature (25°C) environment for 1 hour, test the capacitance at 1KHz/0.3V to see if it is within the specification range.

DF value: After placing it in a room temperature (25°C) environment for 1 hour, test whether the DF value is within the specification range at 1KHz/0.3V.

Tin-eating property: Dip the capacitor pin into a tin furnace (245℃±5℃) for 3 seconds. More than 95% of the pin must be tin-eating.

Withstand voltage: Apply the corresponding AC/DC voltage according to the specifications, and there must be no poor voltage resistance.

Insulation resistance: In a room temperature (25°C) environment, apply 500V DC voltage between the terminals, and measure the insulation resistance value to meet the specifications.

Arc test: In a room temperature (25°C) environment, add a capacitor withstand voltage value (Y1: 4KV/Y2: 2.2KV) between the terminals, set the sensitivity to 6, and must meet the specification requirements. (Y capacitor only)

Terminal load: Apply corresponding tensile force and torque between the capacitor terminals according to the specifications. There should be no terminal breakage or body damage.

Life test: Manufacturer attaches inspection report

Some detailed additions to the X2 capacitor:

1. Capacitor capacity generally has three levels +/-20% +/- 10% +/-5%

2.Loss

Generally, the loss of X2 capacitor less than 0.47uF cannot exceed 0.001 at 1KHz and less than 0.002 at 10KHz.

Generally, the loss of 0.47-1uF X2 capacitor at 1KHz cannot exceed 0.002, and the loss at 10KHz is less than 0.007

Generally, the loss of X2 capacitor larger than 1uF cannot exceed 0.003 at 1KHz.

3. Pressure resistance

The rated voltage is AC275V, AC310V, AC400V

Withstand DC voltage, below 1uF is generally 2200V. There are requirements for the test voltage rise rate, which cannot exceed 1000V/us. The withstand voltage above iuF is lower, generally only 1800V. The test time is 1 minute. The withstand voltage of the capacitor pin of the shell is generally AC2120V. ,1 minute

4. The appearance is clear and the pins are free of oxidation or rust. High-end capacitors have copper pins, while ordinary capacitors have iron pins or alloy pins. There should be no impurities in the packaging material. Check the size.

5. Insulation resistance: The insulation resistance between the two legs is greater than 15,000 megohms, and the resistance between the legs and the shell is greater than 30,000 megohms. The test voltage is 100V.

6. Mechanical shock, mechanical vibration, temperature, and flame retardant properties are generally not inspected or verified by factories.

7. Under normal input voltage, the noise of the capacitor itself is not stated in the general instructions, but it does not mean that the X2 capacitor does not make any sound, especially at the high end of the specified AC voltage. We need to continuously accumulate experience so that we can avoid fewer misunderstandings.