Notes should be paid attention in replacing electronic componients.

When using Semiconductor components: Assemble, transistor, thyristor triac, IC .. we must follow the symbol code; If you have to replace the equivalent type, look up in the manual or at the computer (enclosured  app) and follow the direction. IC is arranged in a row or two rows of conventional conventions as follows: When the IC has a row, looking from the side with the words and symbols, we count from 1 to the last number from the left turn right.
If the IC has 2 rows , based on the marking on the IC body to count the number  1 to n in the opposite direction of the clock, the look up in the manual will know the inner structure.
 

1. If you have to replace the IC with the same  parameters but different number of legs ,  from the  diagram you can hook of the new IC replace in  the circuit that is correct to its funtion. We can replace the approximate type to tranzitor, thyrito, triac. For example: From thyristo manual, we can replace Thyrito EU402Apn 160 A 200V into MCD40-04108.
 
2. There are many legs  in the IC, when using the remaining legs which are not used and connected together; we can  take advantage of the broken legs to replace them. Suppose 1-2-3  is broken if 7-6-5 legs are not used but still good. You can be replaced, by connecting wires. 

3. In all working modes, current and voltage must not exceed the rating of each component: diodes, transistors, thyristors, ICs ...

4. The equipment, circuit board using transistor, IC .. when supplying DC power to the machine  not only have the right voltage but also the right negative and positive wires. Putting Unintentionally  electricity into the reverse circuit, the broken semiconductor will damage components and  the machine.

5. Measuring E-B junction of some transistors, especially high-frequency type, it is recommended to use a large scale, low battery (1.5V) to avoid damage to the ball. When the transistor is being powered, if measure between two C-B poles, accidentally they touch each other; or  measuring IC using a non-pointed measuring stick, it is easy to slip, causing 2-pole short-circuit and damage the components.

6.When bending the diodes or transistors, it is not easy to bend the legs easily, when welding the ball, the torch should be kept away from the legs and there are tweezers pined the ball, both keeping the legs, and radiating heat well.

7. Removing the transistor, the IC out of the printed circuit board, often uses specialized tools to remove all the tins from the legs  and then pull out these components. If there is no suction tool, take a piece of soft stainless copper place it on the IC leg, use the welding  to suck all the tin in the legs, then lift the IC slightly.

Assemble  the transistor or IC into the circuit, must assemble all the legs of components  on the hole of the printed circuit board, then use  the torch to weld each leg in order to avoid the tough of legs caused by a welded pointed.

8. Only use the  welding has welding burnner under 40W, the welding burnner  must be pointed and welded quickly in a few seconds

9. The internal temperature limit of semiconductor components does not exceed the regulation:  capacity of silicon diodes is 150oC, thyristo is 125oC, transistor is  150oC, pedestal  temperature is 200oC, and temperature of cover must be lower.

full capacity listed in the manual, depending on the type, you need to cool in 3 following ways

-Natural cooling by tightening  to metal radiator fans  (aluminum or copper alloy)

- Cooled by forced-draft blower

- Cooling by special liquids, oils or plastics. When installing these components must ensure strong contact between pesdetal and heat dissipation. It must be arranged so that it can be  easily  radiate heat and not to be  placed near other radiant devices.

-If cooled by a fan, it must be installed  the surfaces of the wings radiate parallel to the wind direction; occasionally blowing dust, cleaning dirty oil ... be sure the  good heat dissipation  . The fan must  continously work  with the ball.

-If cooling with oil or water, be sure they are clean, good circulation  not exceeding  the specific level; Do not remove, scrape the thermal  plastic around the padestal.

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