Removing back cover on Acer P191W monitor

[konrad]

Hi,

 

My Acer P191W monitor died the other day and I believe that it may be possible to repair the power board by replacing blown capacitors. My problem is that I cannot get into the monitor. I have removed the base stand and one other screw from the bottom of the monitor but have no idea how to separate the back from the front of the monitor. My hunch is that it snaps together around its edges. Can anyone please advise me if their is a way of separating the casing without damaging it?

 

regards,

 

Konrad

[Plastic Nev]

Hi, not knowing this monitor, I can only guess that you may well be right that most of it will be a snap fit, however do take a look under any labels, self adhesive labels are quite often used to hide the heads of screws, so do have a look under them before trying to prize the edges apart.

 

Nev.

[konrad]

Thanks PN,

 

I have opened up the monitor using a plastic spreader, used for spreading filler. This did not damage the casing. I wonder if anyone can advise me on how to test the capacitors on the power board whilst they are in situ, using a multimeter.

 

Konrad

[KenB]

how to test the capacitors

There is no test that I know of with a meter if the capacitor is on-board.

 

Do it visually. You are looking for blown ( raised ) tops or discolouration / staining.

 

Does this help:

click here

[Plastic Nev]

Hi, now having had chance to do some research, this monitor is an LCD type, this means it will have an illumination lamp or lamps on one or both sides of the screen.

 

Quite a good descrition from that guy as to how to get into the monitor, good find Ken.

 

Do take notice of what he says about being careful with the innards Konrad as damage is too easy to do and difficult to make right.

 

Quite often it is these lamps or the inverter that powers the lamps which fails. You may be able to obtain both lamp and inverter from specialist electronics outlets if no obvious capacitor failure can be seen, as it is easier to replace both than try and fault find on the inverter board.

 

The lamp or lamps are often hidden under a reflective foil on one edge of the screen and when exposed looks like a short and very slim fluorescent tube. It will be the full length of the side it is on, and around 4 MM diameter.

 

Follow the wires from the lamp to the inverter board to find the board.

 

Nev.

[konrad]

Many thanks for the information and excellent photos. Fortunately I had already got this far using much the same method. Some of the connectors are very tight and its tempting to just pull on the wires instead of the block they are in. Resist this at all costs, I did but the needle nose pliars I used slipped and I now have a very nice devils pinch on one of my fingers. No pain no gain.

The capacitors are not showing the bulge I was expecting to see, but comparing them to new ones they do exhibit some deformation looking at them under a magnifying glass. Of course what I really want to do is to take them of the board and test them using a capacitance meter but this could prove to be an expensive way of proceeding as I would have to buy a meter just for this one off job. I have looked at the capacitors in the Maplin catalogue and all are available very cheaply other than the 100 micro Farad 450 V capacitor. This one is not listed. It is very much physically larger than all the other capacitors. If anyone knows where I can get one please do so via this thread. My problem is that the screen just went dead, not on for a few seconds and then dead. Without changing multi components I thought it would be a wise thing just to look at the capacitors as these are relatively cheap to buy and easy to install. Anyway all I have to do now is change them and see what happens. My thanks to everybody for the input so far.

I will hopefully come back soon with a success story to tell providing everything goes back together. The reverse process should be easier. LOL.

 

Konrad:)

[Plastic Nev]

Hi Konrad, I would forget the capacitors for now, if none have exploded or no gunge seeping out of the bottom where they mount onto the board, they are more than likely to be OK.

 

How does the monitor get its supply? Is it from direct mains or through a power supply? If a power supply, it should tell you on its label what voltage should be coming out of it, a test for that at the low voltage end is next.

 

If however the mains power goes straight into the monitor, I seriously recommend to not carry on any further as the risk of an electric shock is severe! Any further testing should only be carried out by trained service personnel.

 

Nev.

[konrad]

Hello PN,

 

The power supply for the monitor is direct from the mains. Knowing the risk involved and taking adequate precautions is the key. I appreciate your concern about the danger when working with mains voltage and I do understand that the capacitor in question may still hold a lethal charge. I would be very surprised if the voltage is anything other than mains ac (240V) although the capacitor is rated at 450V. With this margin of performance capability its odds on that this component will still be serviceable so I shouldn't have to remove it from the board or do anything with it. With the other capacitors running on a low DC voltage the potential for injury is very much reduced provided that they are shorted out when removed from the board prior to testing.

Regarding the meter, I have sent for a capacitance meter on e-bay having watched a clip on U-tube. The model used in the clip was a Newcason XC6013L and will be sent from China including postage for just under £14. Result. My next purchase will be some desolder equipment to help in removing the capacitors from the pcb. Thanks once again for the advice. Will post again when the meter arrives from China.

 

regards,

 

Konrad:)

[Plastic Nev]

OK, so long as you are aware of the high voltage risks, especially if plugged in to the mains which for voltage checks, being mains powered it will have to be, I wish you the best of luck.

However my betting is that all capacitors will be OK and the fault is either an open circuit winding on the mains transformer, a bad soldered joint, or other components, including the previously mentioned lamp or lamps.

By the way that high voltage capacitor is there for smoothing the high voltage needed to make said lamps light up. The voltage is usually created in what is called an inverter circuit, part of which usually has a much smaller transformer than the mains one, I have heard of them frying to extinction but also the transistor that powers it going duff.

Add to that, there could be other faults on the rest of the circuit that handles the raw data, and convert it to enable the screen to show it.

 

Nev.

[konrad]

Hello PN,

 

The weak link(s) in the chain could be anything. From my time working on motor vehicles I always begin with the most simple component, usually the cheapest and then move on to more complicated and usually more expensive items. A process of elimination. You just have to decide when to stop because the cost outweighs the item being repaired, but then monitors are not cheap. My time is free and labour charges are outlandish these days. I just hate throwing stuff away that can obviously be repaired.

One other thing. How exactly do you upload pictures to the threads? I have searched without success to find a solution. It's always helpful to look at pictures when describing a problem.

 

regards,

 

Konrad:wink:

[Plastic Nev]

Hi Konrad, for pictures there are basically two options, either use the forum file up loader, or if a possible future need to post pictures on other forums, you can join a photo hosting site. You upload the photo to the host site, then use a link provided by the host site which you then include in your post here.

Photobucket is a popular hosting site used by many, including myself.

 

However if wishing to use the forums own file up loader, first click the usual "Reply to thread" button, then under the reply box you will see, "Go Advanced", click on that.

 

After writing your post, scroll down to "Attachments" and click the box "Manage attachments" The window that opens, click "Add files", then "select files" you can then browse through your computer to find the picture you wish to post.

 

Nev.

[konrad]

Trying out the upload facility

 

Hello PN,

 

Thank you for the infr on uploading photo's. I hope this effort works. If it does you may be interested in the layout of the pcb from my Acer P191W monitor. It shows the layout quite clearly of the capacitors and other components that you have mentioned in your previous replies. I was wondering if it would be possible to check the continuity (using a multimeter) of the illumination lamp and its inverter/s that you mentioned without stripping off the metal tape and delving deeper into the screen. It would be nice to rule out these particular components, likewise with the transformer/s. I would imagine that if a component is blown their would be no continuity, is that right? Forgive my ignorance.

Once again thanks for the info on uploading. Hope it is attached accordingly.

 

regards,

 

Konrad

[Plastic Nev]

Hi Konrad, the actual lamp tubes themselves, the only test is by putting the high voltage on them to make them strike across, they are a miniature fluorescent lamp with only gas inside, so no continuity at the low voltage of any continuity tester.

 

However, thanks for the photo and I have a couple of suggestions and comments, first is those capacitors look perfectly OK, including the big light green one.

 

I have copied and put some marks on the photo as you will see below.

The black box things I have put a pinkish cross on are I think the high voltage transformers for the lamps as they are near what I assume are the output sockets, marked in red, that go to the lamps. They have a Danger warning and triangle next to them, which is a good indicator they are high voltage.

However one thing I spotted that can easily be tested is a fuse and have marked it in green. What it says by the side of it is T2A meaning it is a 2 amp fuse. If that is blown, then it is a start in I hope a right direction.

 

My Photo is hosted on Photobucket by the way.

 

http://i7.photobucket.com/albums/y282/plasticpig/Monitorboard_zpscac3c986.jpg

[konrad]

Thanks PN,

 

While I am waiting the arrival of the capacitance meter I have been checking the various resistors with my multimeter and I have found at least one that is not giving the correct reading according to the colour coding on it. Another possible fault has been found on one of the blue (capacitors ?) at least that is what I think they are. On the photo previously posted of the main pcb they are shown with what looks like cream blobs on them. I don't know if this is leakage but considering they are identical in appearance they exhibit different readings when tested with the ohm setting on my meter. Having discharged each I then connected the multimeter to charge them and watched the reading. On one it basically started at 0 and then steadily climbed to infinity (good ?). The other just stayed at 0, no increase in charge (bad?). This descrepancy indicates a fault I think. Incidentally these blue capacitors are located either side of a transformer. What do you reckon about what I have found and do you think that these results are significant?

 

regards,

 

 

Konrad:confused2:

[Plastic Nev]

Hi, those cream blobs, if set solid are usually an adhesive put there by the manufacturer to hold them in place.

 

The readings on capacitors must only be taken and believed when it has been de-soldered from the circuit board, any reading you see while still connected could be other components. That holds true of any component on a circuit board, at least one end must be disconnected to get the true value.

 

When removing the electrolytic capacitors, take note of the polarity, there should be a + sign near one of the wires, make sure it goes back the right way round, mark a + on the circuit board if not one there.

 

If still a zero then that is the problem, being small low value capacitors, you may not see much of a charging kick on the multimeter readings, but if you do it is also good news.

 

Did you check that fuse I pointed out and is it showing continuity? If that has blown due to a faulty component it will have to be replaced as well.

 

Nev.

[konrad]

Hi PN,

 

Yes the fuse is OK. I found another fuse lurking in the midst of the cluttered pcb but that is OK too. I take your point about the checking of resistors whilst still on the pcb. I have checked other resistors in situ as the legs are exposed component side up and they check out regarding the values indicated by the colour rings. That's what made me suspect the one that did not give the correct value. I haven't taken any of the capacitors off the board yet as I am still awaiting the capacitance meter from China. I read somewhere recently that pcb's from monitors are not serviceable items. Perhaps some of the components are not readily available and therefore make repair impossible. I will however continue to replace any suspect components that are easy to source and see if it fixes the problem.

I remember once having a TV controller become defective and the man at the outlet said that he did not repair such items so I had to purchase a new one for £34. I took the opportunity to compare like for like when I was able to get into the two pcb's and found the fault within minutes. A faulty ceramic resonator, cost 14 pence. So much for the 'we don't fix these' attitude.

 

regards,

 

Konrad