[captain25]

Hello,

The display was powering on, however, was flickering. I replaced 4 capacitors that were bulged. This fixed the display flickering issue, and monitor was working fine. However, after further testing, the monitor took 1-2 minutes to power on. Each time plugging it in the wall outlet and powering on, the monitor had to "wait" for 1-2 minutes before it would finally turn on. However, soon it wouldn't turn on at all (the power button just blinked for 2 seconds, and that's it). I am suspecting that perhaps the caps were installed in the wrong polarity, however, I made sure that the white lines on caps corresponds to the marked locations on the board. Any ideas would be helpful?

I am from US.

 

[LMiller7]

It is possible that there are other bad capacitors. In many cases a capacitor (or other component) will be bad but show no outward signs whatsoever. Other than trial and error replacement there isn't much an amateur can do.

 

[captain25]

Well, it was almost working when I finished replacing bad caps. However, it started getting worse and worse. I am thinking that perhaps a static discharge could have played a role.

 

[captain25]

Do you think that electrostatic discharge can be considered as an issue?

 

[LMiller7]

Electrostatic discharge can cause a wide variety of issues, some minor, some major. Often there will be no visible sign of the damage. In fact most problems in electronic equipment have no visible signs, bulging capacitors being one of the relatively few exceptions. Diagnosing such problems is usually beyond the abilities of an amateur.

 

[Done_Fishin]

Are you sure that you replaced the capacitors with the correct type, voltage and values ???

Only 105 degree C capacitors should be used with the same voltage rating or higher. The can size should also be the same or larger. The last and just as important factor is that the POLARITY of the capacitor should be the same when inserted in the board .. if you put one in the wrong way round it will slowly fail in the method you mention .. or could even take off like a rocket if you are unlucky!!

As for using 85 degree types .. that could also cause similar problems to those you are experiencing.

 

[captain25]

Yes, I am sure that I replaced the caps with the correct voltage, uFs, and size. They are 105 as well. I inserted the caps based on the polarity markings into the board. However, someone once told me that those markings shouldn't be trusted, since sometimes the markings can be wrong. Don't know if that is true...

 

[Done_Fishin]

Occasionally it is true that a board is wrongly marked for polarity for an individual capacitor but this is very rare .. There are some motherboards in fact that do not use what we call conventional polarity markings and mark the positive pin rather than the negative (Dell comes to mind) but I have never seen this on Monitors (not even Dell)

I have opened monitors though where no caps were showing signs of distress and replacement of all caps in the secondary has brought it back to life. It doesn't always work though!. Another area to look at is the primary side of the transformer. Frequently find there are two small electrolytic capacitors on the smps controller IC, pne of which occasionally causes start up problems. I usually change both.

 

[captain25]

Okay. I will look into these things. I am a novice in electronics repair, and not really sure how to check the primary side of a transformer. Could you give me some tips/steps?

 

[Done_Fishin]

This (the Primary side of the transformer) is not an area where you go poking around with a multi-meter more a question of experience recognizing the components and circuitry then acting accordingly.

The primary side has the incoming AC voltage which is fed through a bridge rectifier to create a DC voltage with a capacitor for smoothing purposes.
Circuits sense the incoming voltage feed it to an Integrated Circuit which will attempt to send pulses to a transistor (might be FET) which in turn switches the smoothed rectified incoming voltage through the primary side of the transformer.
A feedback circuit senses that the pulses successfully passed through the transformer and allow the Integrated Circuit to continue sending pulses otherwise after less than a second they will stop.
most of the integrated circuits that I have come across have 2 small electrolytic capacitors nearby for smoothing or control purposes. Sometimes there is only 1. These are the capacitors that occasionally need to be replaced.

working in this area of the board can be extremely dangerous and should only be attempted by experienced technicians. Some components can store Voltages of sufficient value that death or injury can result when coming into contact with human flesh, even after the power lead has been removed!!

 

[captain25]

Update: Since I couldn't find the same board online, I ordered replacement caps for the other caps I didn't switch.

 

[captain25]

Update: The monitor is fixed! I replaced the other 3 good-looking capacitors on the power board, and everything works fine now.

Thanks for all the help.

 

[Done_Fishin]

Congratulations! Glad we could be of help.

Please mark this thread as solved using the Thread Tools drop-down menu just above your request for help.

 

[ahmed36]

Happy to hear that monitor problem is fixed and it working. Actually capacitors is the main thing for not working this.

 

[Done_Fishin]

Thread marked as solved and closed !