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When the output voltage of the power amplifier power supply chip is normal,

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but the mobile phone still has no service,

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we will continue to the next step: resoldering or replacing the related chip of the 2 g channel

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Here we should pay attention to the related chips of the 2G channel

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00:00:19,933 --> 00:00:23,866

These components are mainly the transmitting power amplifier of the 2 g frequency band,

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and the receiving amplifier of the 2 g frequency band

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00:00:30,066 --> 00:00:36,700

And some models have a small RF antenna switch inside, and some have a total antenna switch

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Because these chips have power supply,

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the chip with power supply has a certain power consumption, which is relatively easy to break

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00:00:50,100 --> 00:00:52,566

These chips also have control signals, components such as filters and normally closed contacts

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00:00:54,933 --> 00:00:59,566

Generally, there is no water corrosion, or there is no false welding caused by the welding position,

12

00:00:59,866 --> 00:01:03,433

which is generally not considered.

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At this time, there is no need to take care of these normally closed contacts and filters

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00:01:11,733 --> 00:01:14,400

This is the problem that needs to be paid attention to. When repairing,

15

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not all original parts need to be considered, and they all need to be moved.

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The filter and the normally closed contact, under the microscope, there is no water ingress corrosion,

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no false welding, then you don't need to touch it, otherwise it will be superfluous

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Especially the handwork is not very good, it is best not to touch it, poor welding will expand the fault

19

00:01:36,266 --> 00:01:40,000

These are the component exclusion methods of chips or sub-chips

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Like filters and normally closed contacts they do not belong to the chip, they belong to a small component

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It's just that the filter has a few more pins than the small component

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How to check the small components in the 2G channel?

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We have a guideline:

24

00:02:02,466 --> 00:02:07,633

Small components have no water ingress corrosion; the welding position has not been dropped;

25

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nor has it been touched by others; false welding caused by incorrect welding

26

00:02:13,066 --> 00:02:15,733

Such small components are not considered

27

00:02:16,600 --> 00:02:20,533

If you have done all the above, but there is still no service,

28

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you can usually find his RF transceiver chip directly

29

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Replace the RF transceiver first

30

00:02:28,500 --> 00:02:33,733

Many mobile phones have no service, usually caused by a damaged RF transceiver,

31

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which can be repaired after replacement

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The replacement of this RF transceiver can also be placed in the first step and the second step.

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When you observe that a main board is not corroded by water

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and the board is very new and has not been touched by anyone, then it is out of service

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At this time, you can also find this chip of the same type as the RF transceiver for replacement.

36

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Or the chip of the same model can be removed from the removal board

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It is also possible to directly replace a radio frequency transceiver first.

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This order doesn't have to be in our sixth step

39

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If the RF transceiver is replaced and the card is turned on, the signal is still no service

40

00:03:16,866 --> 00:03:22,466

At this time, we need to redo the CPU, why do we need to redo the CPU?

41

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Because this is the CPU that contains the baseband CPU

42

00:03:28,066 --> 00:03:32,566

It is due to the false welding of the fault of the baseband CPU, or the CPU has been tampered with

43

00:03:32,800 --> 00:03:36,000

At this time, you have to replace the baseband CPU

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In fact, this baseband CPU refers to a large CPU

45

00:03:40,700 --> 00:03:46,633

If it is a model with a separate baseband CPU, then you need to re-solder the baseband CPU at this time

46

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This is a no service repair

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That's all for this lesson