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.

PSU board​

output filter capacitors​

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

 

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?

 

how can I stop similar electrical failures in the future?

Surge protectors.

Don't know where you're located, but in my area, you can submit claims with the utility company if you think it'll be worth your time.

 

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.

 

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.

 

Is this what you are describing for the top:

 

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

 

Is this what you are describing for the top:
View attachment 222530

the capacitors are rated 25V and 1000 [μF] or 1 [mF] check the new pics sent to Dodgydave

 

I would consider C210 and the one next to it as bulged by that picture. Have you replaced them?

 

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.

 

I would consider C210 and the one next to it as bulged by that picture. Have you replaced them?

I intend to but that's enough work for today
anyway thank you for sharing your knowlage with me

 

Yes yours is also using an opto and tl431 to control the output voltages.

how do you know if an SCR is optic type?

 

A Scr is a Thyristor, what do you mean ??

 

A Scr is a Thyristor, what do you mean ??

you are right it's a solid state relay they are not connected by names. I'm gonna try further solutions such as replacing the capacitors but I'm not sure if the riased output voltage as mentioned in the beginning (15.5V) have caused additional damage to the LCD

 

replaced the bulged capacitors and the LCD is working fine thanks Alhamdulillah

 

replaced the bulged capacitors and the LCD is working fine thanks Alhamdulillah

Make sure you replace both 1000 mf caps are replaced these are poorly made caps in china. Only on the secondary side of the transformer.

kv