How to fix LCD monitor (pics included)

Thread Starter

Mahmoud shiekh suleiman

Joined Nov 17, 2020
8
Hi, few days ago a power brownout happened (power voltage and frequency drop) then completely cut off for few seconds before coming back working regularly, thereafter every electrical installation in the house seemed to come back operating normal as it should be (such as lighting), except for the surveillance monitor which worked for an entire year fine, but now after the incident only the power blue indicator LED works while the crystal pixels remain black no matter what i try of any traditional plug-disconnect repairing method.

now for the last hope I have disassembled the frames of the monitor and explored the internal PCBs, and found 2 things that were not looking well.
first were the rectifier capacitors rated 1000 μF which showed higher values on the multimeter, and 3 of the 4 capacitors had slight bulge in the top (not- sure if the chemicals evaporated). secondly there are 2 levels of DC voltages coming out of the PSU (5V and 12V), the 5V pin showed exact value on the multimeter while the 12V pin showed 15.5V instead. a similar incident happened 2 years back with another monitor after a short circuit happened in a different line in the house and then the old monitor got the same error diplaying black pixels like the new one now.

has anyone had similar problem to this and got any suggestions to fix?
how can I stop similar electrical failures in the future?

Device: MAG 22" monitor
Input voltage: 210-240V, 50HZ
Output voltage: 12V + 5V DC
Operation of PSU type: switch mode power supply
Note: monitor is supplied from a socket that is equipped with a surge protection device.

DSC_0089.JPG
PSU board​

DSC_0090.JPG
output filter capacitors​

DSC_0091.JPG
output voltage pins​
what I think caused the capacitors failure: the voltage drop caused high ripple current in the capacitors and forced them to overheat, but the inrush current of the power could be imminent as well.
although there is an SPD equipped, a voltage rise could have reached the monitor when the power has been cut for few micro seconds
 

jpanhalt

Joined Jan 18, 2008
11,088
Welcome to AAC, Mahmound,

1) The capacitors do not look bulged to me. Sometimes the fracture lines may make them look very slightly bulged. Higher vlaues are not a problem. The tolerance on such aluminum electrolytics is usually quite wide.
2) Sounds like a typical dual voltage supply.
3) If its an LCD, there may also be a negative supply pin.

Is there any contrast adjustment or reset button for the monitor?
 

Dodgydave

Joined Jun 22, 2012
9,919
Switchmode PSUs are usually regulated by optocouplers and a TL431 Zener, yours has an opto and what looks like a TL431 Zener too.
Better pictures of the PCB tracks would be better.
 

Thread Starter

Mahmoud shiekh suleiman

Joined Nov 17, 2020
8
Welcome to AAC, Mahmound,

1) The capacitors do not look bulged to me. Sometimes the fracture lines may make them look very slightly bulged. Higher vlaues are not a problem. The tolerance on such aluminum electrolytics is usually quite wide.
2) Sounds like a typical dual voltage supply.
3) If its an LCD, there may also be a negative supply pin.

Is there any contrast adjustment or reset button for the monitor?
thx
I missed to write the value I got,is it usual the multimeter shows 2.8 mF insted of 1?
also the capacitors top is dent like 1mm outward and it has a ball like shape with precise eye view
when I get time I will try the other control buttons.
 

Thread Starter

Mahmoud shiekh suleiman

Joined Nov 17, 2020
8
Switchmode PSUs are usually regulated by optocouplers and a TL431 Zener, yours has an opto and what looks like a TL431 Zener too.
Better pictures of the PCB tracks would be better.
thanks for replying
I took additional pics as you said
 

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Dodgydave

Joined Jun 22, 2012
9,919
Yes yours is also using an opto and tl431 to control the output voltages.

A sharper photo of the tracks around the small 6 pin chip would be better, as that is the switchmode chip.
 
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