LCD monitor power light flashing but screen is blank

Me too with a Philips monitor. Sorry but because it was a 4 by 3, I decided the best resolution was to ditch it.

If you want to down the path of looking for a faulty capacitor look for a bulging electrolytic. A few years back there was a batch that went market that had serious problems, most ended up in Dell computers.
I hate the throw away mentality and take pride in keeping things working but in this case the rational corner of my brain says treat yourself to flash new one.

I assume "a few years old" means more than three years, because I believe Benq monitors have always had a three year warranty here.

When I had some trouble with a Benq monitor, I found useful information here: Badcaps Forums - Salvation For Your Hardware!

Despite the name, all sorts of problems are discussed there. The fault in my monitor was not due to a dodgy capacitor.

Another site you can try is Austech - Australian Technology Discussion Forum

Thanks guys,
I finally decided to open the monitor up. I usually don't like things that are held together by plastic clips because I always end up breaking the damn thing. But I thought the worse scenario is that I go down to the shop and get a new one. So I went straight in. The BenQ easel was held together by plastic clips only. Using a butter knife, I was able to gently pry it open. I found two capacitors that look slightly bulging on top. What do you guys think? Do they look like the culprit? They are 1000 micro F 16V.

By the way, I don't remember when I bought it but the sticker on the monitor says it is manufactured in Aug 2008. So I'll say it is truly out of warranty.

They're crook, replace with higher voltage ones.

Originally Posted by phild01

They're crook, replace with higher voltage ones.

agreed

Just be careful. Capacitors acts like batteries, those ones will be okay but anything near the 240v side of things might give you a tickle.

I wish you luck in your search for possibly faulty electrolytic capacitors in the device with which you are concerned. In a case such as this, my point of view is - since it will probably cheaper to replace it than having a "professional" try to repair it, there is but little chance of loss in attempting ones own repair - providing any such cost is substantially less than the cost of any replacement device.

The following is a site which discusses manufacturers which are "known" to have produced BAD electrolytic capacitors. Any capacitors labeled as being produced by any of these manufacturers in recent years probably should be replaced with electrolytic capacitors produced by other manufacturers and obtained from reliable sources. (e.g. Jaycar or Altronics in Australia)
List of Bad Cap Manufacturers - Badcaps Forums

If any electrolytic capacitor is bulging or has anything that looks like "goo' emerging from it, it MUST be replaced.

Have you confirmed that it is the monitor that is at fault ?, a flashing power light may mean that it is in power saving mode which most monitors will switch to when there is no input signal.
To confirm that the monitor is at fault I would connect it to another PC, if the monitor works OK on another PC it may be the video board in your PC that is at fault.

I've fixed it. I went down to Jaycar and bought 2 of those Capacitors 1000 micro F and 25V (higher than 16V as suggested by Phild01) and some aluminium tape. Ripped out the crook ones and soldered the new ones on and now it's working. Thanks for all the advice. Cost = $1 per capacitor.

I'm happy

Great result well done!

Originally Posted by justonething

I've fixed it. I went down to Jaycar and bought 2 of those Capacitors 1000 micro F and 25V (higher than 16V as suggested by Phild01) and some aluminium tape. Ripped out the crook ones and soldered the new ones on and now it's working. Thanks for all the advice. Cost = $1 per capacitor.

I'm happy

Out of interest, what was the "Brand" name of the faulty capacitors?

I threw them out. I think they are called Elite.

Originally Posted by justonething

I threw them out. I think they are called Elite.

The name Elite is clearly visible in your photo on some of the caps.

BTW, what did you use the aluminium tape that you got for?

Ozcar,
The PCB and the power supply is covered with a steel shield, and the shield is attached to the LCD panel at the back with aluminium tape, probably to minimize radiation and radio interference of the connectors, and then everything is housed inside a easel. I just replace the tape that I ripped out.

Originally Posted by justonething

I threw them out. I think they are called Elite.

As Ozcar said "The name Elite is clearly visible in your photo on some of the caps."

I note the bulge on the top of the 1000 uF 16 V electrolytic capacitors in the photo. However, the other Elite (35 V) capacitors do not appear to have a bulge on their tops - YET!
We hope that they remain OK but they may cause a fault in the future.

My thought in asking for the Brand name was to update the details in the site which I mentioned earlier.

Originally Posted by justonething

I threw them out. I think they are called Elite.

I just found the following site w.chinsan.com/en/precautions.php

Here the company concerned claims
"We have recently detected some counterfeit capacitors been sold on the worldwide market labeled with the ELITE brand. These counterfeit capacitors have not been sold through the official channels of our sales branches, sales subsidiaries and distributors. We are very concerned about the negative impact these counterfeit capacitors may have on your products as unlike real ELITE capacitors, they do not meet the quality assurance standards of JIS-C-5101-4. ELITE is actively working to eliminate counterfeit capacitors, however, unfortunately it is difficult to rule out all the unofficial channels completely. These counterfeit capacitors show close similarity to our regular products and it is difficult to distinguish and recognize them by appearance alone."

You know, it may not be that the capacitor is dodgy but the circuit design may not have been quite right. Maybe those capacitors are working at their voltage and thermal limits. Upping the voltage may help. I had a Strong PVR and Panasonic VCR that were notorious for faulty power supply capacitors. Kept replacing them. Something about switch mode power supplies needing to be spot on by design. I put it down to high voltage supply to my house.

If you are concerned about thermal limits, you should look for 105 degree rated capacitors (many are rated at only 85 degrees).

Also, "low ESR" capacitors are often recommended. ESR is Equivalent Series Resistance, a property of capacitors which tends to increase a lot when they go bad. This fact gives a way to test capacitors without having to remove them from the circuit, but you need a meter capable of measuring ESR (I have one of the classic Bob Parker meters).

I have also encountered devices that devoured capacitors. I had a particularly infamous DSE set-top box - I replaced just about all the capacitors in the power supply twice over about four years.

I dug the faulty capacitor out from the rubbish. It was a EJ(M)105degC.
The capacitors were definitely failing, but they hadn't failed completely. Since the monitor was manufactured in Aug 2008. Any counterfeit of these capacitors would have to happen in 2008, and shipped to BenQ without them knowing. I have no idea whether the voltage limit of the capacitors was the problem, but I don't think the temperature limit, which is 105 deg would have been a problem.
Since it is a common problem according to my google research, It is possible that there was a whole batch of bad capacitors during that time. Or alternatively, it could havebeen a bad design where the capacitors were undersized.

If you are really curious, if you post the caps to me I could test them for you (capacitance and ESR, leakage too maybe).

As I understand it, 105 degree capacitors may last longer at higher temperatures, even if they don't really get up near 100 degrees.

Ozcar, if you wouldn't mind doing that it would be great. If you PM me with your address. I'll drop it in the post monday. I think there is a bit of interest on the forum to know more about this.
I also have a multimeter that supposedly measures capacitance, but all it gives me is 0.130 nF or 0.L uF. It uses AAA batteries. I'd say it doesn't have enough power to charge up these cap to measure them directly.

OK, message sent.

Ozcar,
I dropped it in the post, it should be there in the next day or so.

One capacitor arrived here today - I thought you found two bad ones, but maybe I was just confused as usual.

I see the markings include "EJ(M)". Best I can figure from the Chinsan (Elite) web site is that the EJ is the "series" number and the M might indicate the capacitance value tolerance of +/- 20% . If it is EJ series, I note they class those as "low ESR" types. If that is not what you replaced it with I wouldn't worry about it at this stage though.

I got the following measurements:

Capacitance 290 micro farads.

ESR 1.6 ohms.

Leakage @ 15V, after charging for 2 minutes, 5mA.

The capacitance of course is less than half of what it should be. So, I guess you could say it is in-capacitated.

ESR is anywhere between 10 to 25 times higher than it should be. Depending on the circuit that sure could be enough to cause trouble. I've seen a lot worse though.

The measured leakage current was over thirty times more than it should be (it should be a maximum of 160 micro amps if I am reading the EJ specs correctly). That might not in itself cause a problem (again depending on how it is used), but it adds to the evidence that the cap is certainly not well.

A big Thank you Ozcar for the info. I did indeed replace two capacitors. But I was too quick in throwing them out and only managed to retrieve one from the rubbish bin. Both capacitors were of identical specification and they appeared to be bulging in the same way. Perhaps they suffered the same fate.