Tech: Screen Display flickering, why ?

Subject: Tech: Screen Display flickering, why ?
From: Murray MacLeod
Date: 31 May 08 - 06:52 PM

My screen display starts flickering after say 30 minutes of being on the internet, at first intermittently and after another ten minutes uncontrollably. It is more apparent when using YouTube than when accessing text based sites.

I am assuming that this is due to the CPU overheating, and that it will require the heatsink removed and the thermal pad replaced.

Is this a reasonable assumption ? Or is there some other possible explanation ? ( I have recently changed my IP from AOL to NTL, cable modem, if that is of any significance)

As ever, thanks in advance for any advice ...

Subject: RE: Tech: Screen Display flickering, why ?
From: Bernard
Date: 31 May 08 - 07:25 PM

There could be a few explanations, but I would think the most likely is a cooling fan failure... if there is a cooling fan on your video card, that is the most likely culprit, if not, then maybe you need to fit a case cooling fan or two, or replace any that no longer function!

If the CPU heatsink was at fault, the CPU would die fairly quickly, so you can probably discount that possibility.

Subject: RE: Tech: Screen Display flickering, why ?
From: JohnInKansas
Date: 31 May 08 - 08:36 PM

The most likely cause is graphics card overheating, but especially with a CRT monitor you might (also) have some hot spots inside the monitor. Either can cause unstable pictures after running for a while.

Some, but not all, graphics cards have a heat sink and fan on them. Nearly all CPUs recently have a heat sink and fan. While the CPU isn't likely to cause the problem described, if one is dirty enough to affect cooling it wouldn't be a bad idea to check both and, if necessary, clean out the crud.

If the fan on either is removable without removing the heat sink it's usually a good idea to pull the fan off and clean the fins on the heat sinks. Most such "coolers" blow air onto the heat sink fins, so that's where the crud accumulates. Often, with the fan in place it may look clean when there's quite a lot of gunk inside (on the other side of the fan).

If you have to actually remove the heat sink (i.e. if it's integral with the fan) it's very important that you apply a proper "heat sink grease" when re-attaching the sink, especially for the CPU cooler. Your CPU will burn itself up without a proper grease coating, if one is needed.

Most recent computers monitor CPU temperature, and if it exceeds expected limits will shut down your computer and give you an error message to the effect of "Your computer has been shut down due to a thermal event. Check your cooling systems." (Messages vary.)

In the absence of an error message, it most likely is the graphics card, with the monitor second most likely. Unless you have an exotic "gamer card" a replacement graphics card might be the best fix, since a card that begins "shutting down" due to heat is probably "cooked enough" to continue to fail. Fairly decent cards are available from $20 - $80 (US) the last time I looked, depending on what you need. (Exotic cards can run up to $400 or more, but you probably don't need one of those.)

For some computers with "integral graphics" - i.e. on the motherboard, you might have to move a jumper to disable the old graphics; but usually you can just disable the old one in Control Panel and let the computer "discover" the new one when you reboot - assuming that you have a slot available to plug a new card into.

Flicker will sometimes happen due to a bad capacitor or leaky diode in a CRT monitor, but most shops consider CRT monitors "not economically repairable." Since some of the internal components can hold kilo-Volt charges long after being unplugged, and "capacitor memory" can recharge those voltages even if you short them out to discharge them, attempts at internal repairs are not recommended if you don't have a very good idea what you're doing (and/or an excellent insurance policy to take care of your loved ones when you're gone).

John

Subject: RE: Tech: Screen Display flickering, why ?
From: JohnInKansas
Date: 31 May 08 - 08:50 PM

Cross-posted I guess? (or I wasn't thinking about the whole story?)

As Bernard suggested, do check out the main case cooling fans. If needed, replacements shouldn't run over $20 (US) each, and with recent case designs they're pretty much a "snap in" replacement. With older cases you might have to actually turn about 4 screws.

Case fan failures usually produce other symptoms, but they might be involved and should be checked occasionally just on principle. Note that in some newer designs it's normal for the case fans to run only intermittently. Usually one that's gone bad will be full of junk, stiff to turn by hand, or otherwise obviously degenerate.

John

Subject: RE: Tech: Screen Display flickering, why ?
From: Murray MacLeod
Date: 01 Jun 08 - 01:24 AM

Thanks for your input, Bernard and John.

I don't think it's the monitor, it is a modern flat screen. The graphics card is integral with the motherboard (I think)


If the fan on either is removable without removing the heat sink it's usually a good idea to pull the fan off and clean the fins on the heat sinks. Most such "coolers" blow air onto the heat sink fins, so that's where the crud accumulates. Often, with the fan in place it may look clean when there's quite a lot of gunk inside (on the other side of the fan).

That's what I think is the problem, but how would you know if the fan is removable without removing the heat sink ? There are two grey levers which lift up on either side of the fan can I just pull the fan off without disturbing the heatsink ?

Subject: RE: Tech: Screen Display flickering, why ?
From: GUEST,Jon
Date: 01 Jun 08 - 01:34 AM

Enter the BIOS, (most commonly press F2 or delete when booting) and have a look and see if there is a page monitoring the hardware. You might for example be able to see the CPU temperature changing as well as perhaps whether fans are running.

Try a visual check that fans are spinning and vents on the case are clear too.

Subject: RE: Tech: Screen Display flickering, why ?
From: GUEST,Jon
Date: 01 Jun 08 - 01:45 AM

Also, you may have some software monitoring tools you can use while your using the PC. eg. I can find out the "core temperature" of my GEForce 8500 GT card using a nVidia utility (and if they can provide that for Linux, I'm sure there must be more around for Windows).

Subject: RE: Tech: Screen Display flickering, why ?
From: The Fooles Troupe
Date: 01 Jun 08 - 02:17 AM

"There are two grey levers which lift up on either side of the fan"

These may actually unplug the CPU itself. As long as you don't separate the fan as JiK mentions, and take anti-static precautions - mentioned elsewhere - so as not to damamge the CPU, probably no great harm will be done.

A tip - if your PC case stands on the floor (carpet or not), it is more likely to pull in dust.

Subject: RE: Tech: Screen Display flickering, why ?
From: JohnInKansas
Date: 01 Jun 08 - 02:28 AM

Murray -

There are lots of different kinds of CPU heat sinks, and I've seen only a few of them. In a couple that have "needed cleaning" recently the fan had four screws in the corners to hold it against the finned heat sink. The "clamping device" held the finned heat exchanger against the CPU. Pulling the screws let the fan come off without moving the heat sink, so you could see that the fins of the sink were full of our usual household kitty fur. (These were in fairly "cheap" computers and didn't have particularly high-powered processers.)

If there's a clamping device, it's more likely that the fan may be integral with the finned exchanger and the whole unit will come off as one piece, but in some designs even if the finned exchanger is "unclamped" when you release the clamping device it could be left in place and only the fan lifted off.

If it's a fairly recent model computer, your operators' manual may have some helpful description - and if it's recent enough you may be able to find a (service or operator) manual at the builder's website.

If necessary, it shouldn't be hard to find an appropriate heat-exchanger grease. It usually comes in tiny "toothpaste" style tubes. Since any air in the gap between the "fin" unit and the CPU case acts as a thermal insulator, the grease is basically just to fill the gaps. Almost any non-corrosive gunk that excludes all the air bubbles would do; although most electronics-grade greases are "filled" with silver or other thermal-conduction-enhancing gunks. Getting a fresh "electronics grade" grease assures that the "non-corrosive" part of the requirement is probably met, which might not be quite the case with "similar products" from the auto parts shop.

Sometimes there may be enough of the original grease to be smoothed out and the exchanger reseated, but it really is best to use a fresh coat with new grease, since the old grease may not "flow" as well if it's been well cooked, and any "edge grease" that gets stirred back in may have lumps of extraneous crud in it.

John

Subject: RE: Tech: Screen Display flickering, why ?
From: Murray MacLeod
Date: 01 Jun 08 - 03:44 PM

many thanks to those who have offered help, and I think you all had the right idea, that there wasn't enough airflow.

when I last closed down, I took the top and sides off the tower and I noticed that the power supply felt uncomfortably hot.

half an hour later, I rebooted the machine with the top and sides off, (that was three hours ago, and there hasn't been a flicker on the screen display since then, despite having been accessing YouTube constantly during that time ).

ergo, there wasn't enough airflow (although why it should suddenly have become a problem beats me)

so my intention is simply to leave the top and sides off, and as the tower sits under a desk, there shouldn't be any problems.

every so often I will take it to my workshop and give it a good blow out with compressed air, to remove any accumulated dog hair etc ...

thanks again to all who responded.
.

Subject: RE: Tech: Screen Display flickering, why ?
From: Nigel Parsons
Date: 01 Jun 08 - 04:14 PM

Murray,
Surely the sides are there to prevent all the crud from getting inside your machine.
The vent holes on the sides where the crud collects do a marvelous job in locallsing the dirt collection. Cleaning these occasionally (and not covering with books/post-it notes) Should keep the machine running without the risk of leaving it open to the elements.

Cheers
Nigel

Subject: RE: Tech: Screen Display flickering, why ?
From: Murray MacLeod
Date: 01 Jun 08 - 04:53 PM

Hi Nigel, I have just reached under my desk and felt the power supply, it is as cool as a cucumber, (after 5 hours use ) and the screen display is still perfect, so I shall now try putting the sides back on.

maybe it's the top panel that is the problem, it could be preventing the heat from the power supply from dispersing.

I am not worried about dirt collecting, I have a very efficient compressed air system which will blast out any accumulated crud.