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LB3980 MOSFET replace

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Once MOSFET in LB3980 is damage, you have to replace it to enable LB3980 work normally again. For the detailed instruction, please see below. Before the replacement, please make sure you have the replaced part same like the previous broken part. Pease firstly check Fig 30 in Page 16 for the part number (like 1XTP200N10T).

Fig 1

This is the whole 3980 unit (hereinafter referred to as “monitor”). We will show the operation of changing the MOSFET (Metal Oxide Semiconductor Field Effect Transistor).
1. Separation of the case.

Fig 2

NOTE: There are 17 pieces of screw fixed in the case. Please separate them with screw driver one by one
Separate the electric fans (Note: The six electric fans connects with the covering above the monitor) first. The covering connects with the monitor by 9 pieces of screw and two lines (a red and a black one which will note below).

Fig 3

Cut the white binding line (the line is in the red circle).
NOTE: The binding line is used to connect electrical lines so as to avoiding them drawn into the electric fans.

Fig 4

The two lines are the electric fan’s lines connecting electric fans and the monitor. There is a white connection between two lines and the connection is fixed with white gum. The screen is showed as above.
Remove the gum and then pull out the connection.

Fig 5

Fig 6

After the separation of the two lines, the inner construction of the monitor is showed on the following screen.

Fig 7

Cut those binding lines in the red circles See screen as below:

Fig 8

Fig 9

After cut those binding lines, the inner core of the monitor will be separated from the covering only when five lines are cut. The screen is showed as below:

Fig 10

NOTE: 1.The 1 line is the line of USB, and you can see the word like “USB_HOST” near the connection.
The 2 line is the line of keyboard, and you can see the word like “Key.IO” near the connection.

The 3 line is the lead of the monitor, and you can see the word like “J-RS485” near the connection.
The 4 line is the line of aerial
The 5 line is the line of the screen. It is the shortest line among those five lines, so it must be separated at last.
2. The separation of those five lines is the most important operation for removing of the covering, so it must be separated carefully in the sequence showed above.
3. Those five lines are fixed with gum, so you need to remove the gum first and then pull them out. (Warn: please do not cut those lines with scissors.)
You can refer to the screen showed below: Pull out the first line:

Fig 11

Pull out the second line:

Fig 12
Fig 13

Pull out the third line:

Fig 14
Fig 15

Switch the fourth line with pincers and pull it out:

Fig 16

Fig 17

Remove the gum and then pull it out:

Fig 18

Fig 19

So the case is totally removed from the core. It is showed on the following screen. Next the upper core should be removed.

Fig 20

2. Separation of the core
There are six screws and a belt (it will be showed on the following screen) fixing the upper core with the lower core. Remove them off with screw driver and pincers one by one. See the following screen showed as below:

Fig 21

Fig 22

Open the belt which is the connection of upper core and lower core except for those six screws. The screen is showed as below:

Fig 23

Fig 24

Next the upper core is opened.
NOTE: Another side of the upper core is connected with the lower core with lines and it cannot be opened.

Fig 25

Fig 26

3. Replace the MOSFET
The measurement of the bad MOSFET.
NOTE: It is a very important operation to measure the quality of MOSFET and the quantity of the bad MOSFET.
The method: Find a multimeter and switch to the resistance measurement. Put the red pen to the earth line and the black one to the MOSFET to find whether there is a value or not. If there is a value, the MOSFET is normal; if not, the MOSFET is bad. Check each MOSFET one by one. See screen as below:

Fig 27

There are two pieces of screw on the core. Remove them out. See screen:

Fig 28

Fig 29

The MOSFET (black chips) is showed under the core. See screen:

Fig 30

The bad MOSFET is showed in the red circle on the following screen. Use the screw driver and pincers to remove the screw.

Fig 31

Fig 32

NOTE: There are two lines connecting MOSFET with the core. Take care for the two lines when the MOSFET is removed.

Fig 33

After remove the screw, the iron sheet and the MOSFET, and there is a insulation piece on the core and a insulation pipe in the hole. Keep them with care. See screen as below:

Fig 34
Fig 35

Clean the core and replace a new MOSFET on it.
First put the insulation piece on the core and then the MOSFET next the iron sheet and last the screw to fix the MOSFET. The sequence of the screw install is showed on the following screen.
First put on the insulation pipe.

Fig 36

Next the nut etc.

Fig 37

NOTE: You are note to connect the two lines with MOSFET which is showed before.
4. Combination of the core
After install the MOSFET, and then combine the whole monitor. Open the switch of the belt.

Fig 38

Close the belt to combine the upper core and the lower core. The switch will be closed automatically if you put it into the connection.

Fig 39

Install the six pieces of screw which is used for fixing the upper core with the lower core. See screen as below:

5. Combination of the case

Fig 40

After putting on the six pieces of screw, the five lines which are the connection of the case covering and the core will be connected. The steps go as the same with those of removing the lines. See the following screens.
Connect the first line.

Fig 41

Connect the second line

Fig 42

Connect the third line

Fig 43

Connect the fourth line

Fig 44
Fig 45

NOTE: If you have the gum, it is recommended to scrawl a little to fix the connection firmly.

Fig 46

Fig 47

At last, the fifth line of display screen

Fig 48

After the connection of those five lines, and then check the monitor is normal or not. Connect the current line with the monitor and switch on the power.

Fig 49

Check the screen, the keyboard is normal nor not. If it does not work, please check those lines are well connected or not, or contact with us as soon as possible; if it works normal,

and hen goes on to the next step.
Connect the line which is the connection of the monitor and the electric fans covering. First, fix those electrical lines with binding lines.

Fig 50

Fig 51

Next connect the connection of two lines

Fig 52

NOTE: You are noted the two lines direction. The black line to the black; the red line to the red. See screen showed as below:

Fig 53

Then fix the two lines with binding lines. See screen:

Fig 54

Close the electric fans covering and fix it with pieces of screw. The screen is showed as below:

Fig 55

Fig 56

The replacement of the new MOSFET is finished. Please connect it with testing wires and have a testing.

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