Case Study 1

 Resistance Resistor

Capacitance: Capacity

Inductance: Inductance

Diode: Diode

Triode: triode

Field tube: field effect transistor FET

There are also certain rules to follow for the identification of components on the main board: (All the screenshots are from CT3 material board)

1. The logo of the resistance contains the letter "R"

In addition, there are thermistors marked with RT or RH at the beginning.
2. The logo of the capacitor contains the letter "C"

3. The logo of the inductance contains the letter "L"

4. The logo of the diode contains the letter "D"

 

(1) PD25 and PD26 in the above figure are single diodes. Using the forward conduction characteristics of the diodes, the conduction value measured on the main board with the diode position (the multimeter is: FLUKE15B the same below) is 228, and the components are removed to measure Value: 260 Carefully observe that pin 1 and pin 2 of PD22 on the motherboard are connected, so it is also a single diode. The conduction value measured online is 125, and the measured value is 133 when removed

(2) PD34 is a dual diode. Its internal structure may have the following situations:

             When ABC
is measured online with a diode file, touch any two feet with black and red test leads, and there are readings in the six measurements. It seems that the online measurement is not accurate at this time. Either the component is damaged, or the reading on the multimeter is affected by the peripheral circuit. Remove the D34, and there are two readings in the six measurements: when the red pen is connected to pin 3 and the black pen is connected to pin 1, the reading is 557; When the red pen is connected to pin 2 and the black pen is connected to pin 3, the reading is 553.

According to the forward conduction characteristics of the diode, this double diode belongs to the "end-to-end connection" type, that is, type A
(3)

In the above figure, the types of the double-diode PD30 and PD40 can be measured online, which are B type and A type respectively. 5.
The identification of the triode and field effect tube on the main board contains the letter "Q"

 

On the reverse side of this part is a power management chip MAX1999, which controls two PWM circuits. Combined with the tinfoil wiring on the motherboard, it can be determined that this is part of a PWM circuit. PQ154 and PQ155 are the upper and lower tubes, and they are single MOS tubes.

Take off PQ154 and PQ155 respectively, and measure D and S poles alternately with black and red test leads. When the red test lead is connected to the S pole and the black test lead is connected to the D pole, there will be readings: the reading of the upper tube is 510, and the reading of the lower tube is 189. Both are N-channel single MOS transistors. The silk screen mark on the surface of the upper tube is 4800B, and the silk screen mark on the surface of the lower tube is 4702. The materials used for the upper and lower tubes are different. Observe the periphery of PQ142 and the corresponding reverse side. This tube should be a dual-channel MOS tube of another PWM circuit controlled by MAX1999.

After measurement, it is found that S1 is grounded, and S2 is connected with D1. Therefore, it can be visually understood that the left half of the PQ142 in the above figure is the upper tube, and the right half is the lower tube.
Next, judge the type of PQ142, as shown in the figure below, use a camera and ferrochrome to pry open D1 and D2 of PQ142, so that these four feet are separated from the pad.

 

Adjust the multimeter to the diode level:

(1) When the red pen is connected to D1 and the black pen is connected to S1, the reading is infinity; when the red pen is connected to S1 and the black pen is connected to D1, the reading is 173.

(2) When the red pen is connected to D2 and the black pen is connected to S2, the reading is infinity; when the red pen is connected to S2 and the black pen is connected to D2, the reading is 485. It can be known that PQ142 is a dual N-channel MOS transistor.

 

Observe that the four pins 1, 2, 5, and 6 of PQ127 in the above figure are connected, which conforms to the characteristics of a single MOS tube. Press the MOS tube directly to measure. The four pins connected are the D pole, the 4 pins are the S pole, and the 3 pins are the G pole. After measurement, when the red pen is connected to the S pole and the black meter is connected to the D pole, the reading is 520. Therefore, it is an N-channel six-pin MOS transistor

 

The observations of the sesame tubes Q54 and Q55 in the above picture are fruitless. It may be a triode or a field effect transistor. It can be assumed that it is a triode to measure, take it off and measure any two pins alternately with red and black test leads, and there is only one reading: when the red pen is connected to pin 1 and the black pen is connected to pin 3, the reading is 598, which can be judged as N ditch Dojo effect tube. Carefully observe the surface of the components, the silk screen code is "W2E", so we can know that all the components on the motherboard are N-channel field effect transistors.

In the picture above, MQ1 looks like a field effect tube (not necessarily true), take it off and measure the diode value of any two pins alternately with red and black test leads. There are two readings in the six measurements: when the red pen is connected to pin 2 and the black pen is connected to pin 3, the reading is 586; when the red pen is connected to pin 2 and the black pen is connected to pin 1, the reading is 600. It can be inferred that MQ1 is an NPN transistor.

 

According to the silkscreen, the sesame tube in the picture above is Q33, measure according to the above method: connect the red pen to 3 pins, the black pen to 2 pins, the reading is 639; the red pen to 1 pin, the black pen to 2 pins, the reading is 641. It can be inferred that Q33 is a PNP transistor.

 

Q40 in the above figure should be a field effect tube after observation. After measurement, when the red pen is connected to D pole (pin 1, 2, 5, 6), and the black pen is connected to pin 4, the reading is 418. Therefore, the component is a P-channel field effect transistor.
The observation of Sesame tube Q41 was fruitless. It may be a triode or a field effect transistor. It can be assumed that it is a triode to measure: in the road test, use the red and black test leads to measure any two pins alternately, and the readings are infinite. Take it off and get the same result. Chatto learned that it has integrated resistors inside. It seems that this method is not suitable for all triodes.

 

In addition, the components marked with the letter "U" on the motherboard are integrated ICs. Some are easy to distinguish, for example: the south bridge on the CT3 material board is marked as U40, the north bridge is marked as U38, the EC mark is U23, the card reader chip is marked as U21, the marks of sound card, power amplifier, MODEL, network card, EEPROM, power management chip, etc. Both contain the letter "U". Of course, there are still some components marked with "U" that are not easy to identify. For example, there is a five-pin chip marked with U near the two USB ports of the CT3 material board.

 

 

Carefully observe the above figure, the first pin of U33 is connected with the first pin of the USB interface through the 0-ohm resistor R682. It can be seen that this five-pin chip provides power for USB.

 

Seeing U1, U2, three 0-ohm resistors, and three triodes, it is natural to think of the R, G, B and line and field signals of VGA. If U1 and U2 are gates, their pins should be connected to the row and field pins of VGA. Adjust the multimeter to the diode level, connect one test lead to pin 13 of the VGA interface, and draw the other test lead on the pins of U1 and U2, and find that the first pin of U2 is

The value of pin 4 and pin 13 of the VGA interface is 17; similarly, the value of pin 4 of U1 and pin 14 of the VGA interface is 17. On the front and back of the VGA interface, it is found that the resistance marked 390 is connected between them.

Also near the South Bridge, we can also find two five-pin chips with the letter "U" in their logo

It can be known from experience that the function of the two five-pin chips is to convert the reset signal sent by the south bridge.

In short, for the identification of components on the motherboard, there must be not only relevant theories as the basis, but also rich maintenance experience as the foundation.