Why do Digital Displays have a Screen saver. When CRT's Don't? - Page 1
Forum section: electronics / general

author: Labrat101
author_rank: Unknown
timestamp: June 06, 2020, 02:26:46 pm
content: Here is The Question.That over 50 years in electronics no one has Yet given me a Good Answer .Why do Digital displays have a screen savers when CRT's Don't?All the CRT's and analog scopes . I have ever used or seen Don't have a screen savers .To stop that nasty screen burn. which plagues them All. Also the Plasma & Phosphor screens suffer from screen burn .I have never seen screen burn on a Digital screen . ie LCD, LED, But all have a screen saver .. Why.. ??Yes I know its a silly Question but does any one Know the Real Answer."To me its like inventing the Gate after the cows have all run out of the field . "So I would like to hear from all .. WHY. ??RNS

author: Zero999
author_rank: Super Contributor
timestamp: June 06, 2020, 04:43:15 pm
content: I've never seen a screensaver on any oscilloscope.There won't be a screensaver on an analogue oscilloscope because it's not something which can easily be implemented using analogue circuitry.If a modern digital oscilloscope has a screensaver, it will just be for marketing or a novelty.

author: Siwastaja
author_rank: Super Contributor
timestamp: June 06, 2020, 04:49:39 pm
content: Never seen one either, so the claim that "all" have it is not on a very stable ground.IIRC, I think I have seen a screensaver on an Agilent digital storage oscillosscope, but thatwasa CRT.Analog scopes could implement "screensaver" in a form of turning the thing off automatically after a set time of no setting changes, but people hate such auto-off features. Engineers want a reliable device that doesn't fuck with their work, because their worktime is more valuable than the fact that instruments wear out and must be replaced. Analog scopes require some understanding, you need to be quite stupid to really burn the phosphor. Most people understand not to do it.

author: 0culus
author_rank: Super Contributor
timestamp: June 06, 2020, 05:07:57 pm
content: Tek scopes with an mcp crt (7104, 2467) have a protection circuit that (at least in the 7104) shuts off the crt based on a combination how bright the display is set and timing. The brighter you set it (I think it's actually looking at grid current or something), the faster it shuts off to protect the microchannel plate gain. The HP 53310A modulation domain analyzer (and I assume also o-scopes built in the same form factor, using a raster crt) has a screen saver. It's also important to note that electrostatic deflection analog scope crts are not the same as the raster crts that we know and love from televisions and computer monitors.

author: Bud
author_rank: Super Contributor
timestamp: June 06, 2020, 05:19:49 pm
content: Shutting off the crt on analog scopes is your screen saver. The fancy dancing stars and stuff on modern digital scope screens is a habit carried over from computers.

author: TomS_
author_rank: Frequent Contributor
timestamp: June 06, 2020, 05:24:34 pm
content: Keysight scopes have a screensaver, which is basically their logo drifting around the screen.

author: ucanel
author_rank: Regular Contributor
timestamp: June 06, 2020, 05:47:23 pm
content: Quote from: Bud on June 06, 2020, 05:19:49 pmIf i recall correctly, desktop pc that i had 15 years ago was doing the same thing as a screen saver mode.There was just the hissy crt screen energising sound i remember.

author: Zero999
author_rank: Super Contributor
timestamp: June 06, 2020, 06:07:40 pm
content: Yes, blanking the screen is the old fashioned screensaver. I was thinking of the modern fancy screen savers of course. CRTs don't like being turned on and off too often, so it can't kick in too often.

author: Labrat101
author_rank: Unknown
timestamp: June 06, 2020, 06:43:38 pm
content: When I said screen saver that is what's is in the menu of most Digital scopes . with set time in minutes etc.Yes .Very annoying as the screen goes blank in the middle of working. (yes I disabled it )On the big CRT scopes it would be useful if the brightness would turn down automatically on temperature or after 4 or 5 hoursto save the screen burning . But that feature was never implemented .As mentioned turning them on & Off is not good.Thanks for some Good Answers ..

author: David Hess
author_rank: Super Contributor
timestamp: June 06, 2020, 07:41:31 pm
content: Quote from: Zero999 on June 06, 2020, 04:43:15 pmTektronix oscilloscopes which used microchannel plates for image amplification have protection in various forms including blanking tied to intensity and time on the 7104.Many of their other oscilloscopes tracked the beam current for fault protection.QuoteAnd the same applies to a CRT monitor which leads to the answer. LCD displays include a layer of processing between the video signal and display which can implement a screen saver. CRT displays are almost always directly controlled from the video signal so any screen saver has to be implemented in the source.QuoteThe same applies to LCD monitors except in some special applications. Marketing overcomes engineering every time.

author: Someone
author_rank: Super Contributor
timestamp: June 06, 2020, 10:55:57 pm
content: CRTs and LCDs do have burn in, and it varies wildly between different panels/drivers. There are a range of mitigation methods used in products that make it less noticeable, or reduce the accumulation. Screen savers are brute force methods when you don't have anything better.For the high contrast images displayed by test equipment you'll likely never notice the small variations. But in a smooth gradient that same burn in will jump out obviously.

author: langwadt
author_rank: Super Contributor
timestamp: June 06, 2020, 11:11:46 pm
content: Quote from: Someone on June 06, 2020, 10:55:57 pmyep, we used som 7" lcds and they were basically scrap after about month of showing the same picture

author: james_s
author_rank: Super Contributor
timestamp: June 06, 2020, 11:25:42 pm
content: I've seen image retention on LCD panels but usually it fades after a while if you show something else. I've also seen panels that displayed the same image for many years and never showed any kind of retention. There's zero reason to have a screensaver on a LCD scope, although many newer scopes are Windows PCs under the hood so it would not surprise me if the standard Windows screensaver framework can be enabled. I've also heard people refer to the wallpaper or lock screen image on a phone as a screensaver which never made any sense to me, I figured it must be people too young to remember what a screensaver is.IMO the only time screensavers ever made sense was on all-in-one CRT based computers like the compact Macs. Anything with a separate monitor it has always made sense to just turn off the monitor if you won't be using it for a while. If anything, screensavers encourage people to leave a monitor on unnecessarily. I do have fond memories of watching the flying toasters float by though.

author: David Hess
author_rank: Super Contributor
timestamp: June 07, 2020, 12:27:21 am
content: The only LCD panels where I have seen image burn were either high intensity projection displays or defective displays. Projection displays are what I was thinking of when I mentioned exceptions.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 07, 2020, 03:57:37 am
content: Quote from: james_s on June 06, 2020, 11:25:42 pmPorted to several modern platforms.https://www.jwz.org/xscreensaver/

author: 0culus
author_rank: Super Contributor
timestamp: June 07, 2020, 04:20:04 am
content: HP 85662A spectrum analyzer display (8566A/B, 856(7/8A)/B) is another one I forgot about...shift+g to turn off beam and shift+h to turn it on again. Can also be programmed via GPIB.

author: jklasdf
author_rank: Regular Contributor
timestamp: June 07, 2020, 04:23:48 am
content: The Agilent 54622d oscilloscope has a screensaver for its CRT (although it's easier to implement there since it's a digital scope). I think if high-end analog oscilloscopes had continued to be developed into the late 90s, screensavers for the CRT might have become a thing, but for just a plain old analog oscilloscope it seems like a lot of work to implement. The only ones I can think of (as already mentioned) are the Teks with MCP.I don't think I've ever seen a screensaver on a modern LCD oscilloscope, or if they have one it can at least be disabled. Some early CRT DSOs (e.g. monochrome LeCroys) often have pretty noticeable screen burn-in, and really could've used a screensaver back in the day.I've seen some screensavers on LCD TVs when there is no signal, or from DVD players when there's no disc, but otherwise I think they're fairly uncommon on most of the devices I've seen. It kind of makes sense when otherwise it would just display a static error message, but I think screen savers are there mostly for legacy reasons or to look nice nowadays, rather than to prevent screen burn-in.

author: 0culus
author_rank: Super Contributor
timestamp: June 07, 2020, 04:44:23 am
content: I know for a fact that Keysight MSO series scopes have screensavers. It's buried in some settings menu, and by default just blanks the screen and moves the Keysight branding around.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 07, 2020, 07:48:00 am
content: With normal TV receivers & picture monitors, the normal cause of "burn in" could be caused by still images like test patterns, or more often, text, bright white lines on a dark background, large white geometric shapes, etc.The most common cause in TV Broadcasting, however, was deliberate underscan.Older TV tubes had pronounced rounded corners, so if they needed to display a correct 3:4 image, it was common to set the scans to "underscan" to achieve this (it was often provided as a switch function)If, after being set in this manner for a long time, it was restored to "full scan", the burnt on image of the smaller raster would be evident as a sharply delineated area of lower brightness.Until the 1980s, the default with no video input was for the TV/monitor horizontal & vertical scans to "free run" at close to the normal scan rates, & the display to remain visible, basically showing random noise instead of video.If the scans were set to "underscan", it could still cause burn in.Starting in that decade, TV sets were designed to display a black screen when video was lost.Picture monitors did not, by default, do this.When CRT based monitors were used with computers, the usual display was a black screen with white (or green) text displayed upon it.As some text was common to many operations, the problem arose of that text burning in.The computer would automatically generate the "screen saver" when "in standby", but not currently busy.

author: flolic
author_rank: Frequent Contributor
timestamp: June 07, 2020, 10:14:44 am
content: My current laptop (HP ZBook 15 G1) with FHD IPS panel has very noticeable image retention after few hours displaying the same image. It gradually goes away, but previous image is still noticeable after an hour.

author: Labrat101
author_rank: Unknown
timestamp: June 07, 2020, 10:19:02 am
content: Quote from: NiHaoMike on June 07, 2020, 03:57:37 amInteresting . puts a whole new light on magic smoke.This was not quite what I was referring to . . But to screen blanking .screen protection to stop image burn.Which seem to be under the title of screen saver. on many system.After Dark was far better .. ( The man on a desert island )Never did do any work just sat and watched it ..

author: SiliconWizard
author_rank: Super Contributor
timestamp: June 07, 2020, 03:45:37 pm
content: As said above, just blanking the CRT display would have been an easy way to avoid screen burns.On old analog scopes which basically had no "fixed" area of the display, the problem would be minor unless the user left the exact same signal on display for a very long time. Probably not that much of a problem in practice.The problem started to appear when scopes started to have on-screen display of extra information. I guess automatically blanking the screen after a defined amount of time would have solved the issue, but OTOH that could have been pretty annoying for many use cases. Detecting the user is NOT actually using a scope (as opposed to a computer when you can more or less safely assume that if the user doesn't take any action for a while, they're probably not using the computer) is not that trivial. In some cases, you may work with a scope for extended periods of times without touching it, but still looking at it. Guess vendors didn't bother to add this optional feature. And screen burns can be pretexts to buy new gear anyway...It's not a "digital display" (I guess LCD?) vs CRT matter IMHO, more a matter of history. When LCD displays became the norm on scopes, screen savers were already popular on computers, so that became more obvious. Still, I've used quite a few modern scopes that didn't have any screen saver feature (at least that I've known of.)

author: Labrat101
author_rank: Unknown
timestamp: June 07, 2020, 04:33:55 pm
content: Very True.I have 2 analog scopes which I prefer over my digital .Both Have the grid on the screen its self and not on a glass over lay . And both have a visibleBurn marks and I can see the grid even when I turn the display Grid Off.Yes I always turn the brightness down if I am leaving my bench for any length of time.Hp Agilent @ & the big old Tektronix which I repaired and re calibrated Both not so long ago.I did even wonder about putting a small button and relay on the brightness control just to dim the screen to minimum .. Push & Go ..But As every one knows if its working don't fix it. .Thanks for all the feed back . I thought that this thread would never get any replies .As being a Engineer/Tech My self it was one of those thoughts that I came up with while stuck Looking at My screens and wondering why the savers or Blanker were invented nearly 10 years after they were not really Needed....Lock down has a lot to answer for ..I See by all the feed back, this has open a whole new portal .Its the simple things in life that are so PleasingI would Love to Get "After Dark" BackRNS

author: TimFox
author_rank: Super Contributor
timestamp: June 07, 2020, 05:26:57 pm
content: On IPS computer monitors from -hp-, they do not warranty against burn-in caused by a stationary display. They specifically warn against the use of those monitors in a security/surveillance application, where the scene does not change for hours at a time. For that reason, I switched the power settings on my desktop computer to blank the screen after a reasonable dead time.

author: james_s
author_rank: Super Contributor
timestamp: June 07, 2020, 06:01:18 pm
content: Most of the CRT based DSOs and other instruments I've encountered have some screen burn but I don't think it really matters, it's not something you notice in regular use. Burn is an issue on computer displays and arcade games where the display shows vastly different images at different points in time, I remember seeing a lot of computers with a login screen burned in and arcade games typically have "GAME OVER" and scores and such burned in. A scope though always displays roughly the same thing, a graticule, menu grid, maybe some text. It's rare that large areas of the screen are illuminated which would make the burn visible.

author: David Hess
author_rank: Super Contributor
timestamp: June 08, 2020, 12:30:05 pm
content: Quote from: jklasdf on June 07, 2020, 04:23:48 amMCP oscilloscopes are a special case because the MCP has a limited operating life.Quote from: SiliconWizard on June 07, 2020, 03:45:37 pmYou have to be careful about blanking a CRT. Extended operating time with the heater active but no cathode current can damage the cathode. (1) This becomes a problem in applications where the instrument is powered for long duration but the CRT intensity is turned off to preserve the CRT. Turn the intensity down, but not off, and defocus it if you must.Vacuum tubes have the same problem when operated in cutoff. Special cathode materials were used to avoid this issue in applications where operation in cutoff would be routine like digital logic.The above suggests that analog oscilloscope CRTs were constructed to operate in cutoff, at least after the problem was recognized, but *raster* CRTs were not.(1) Robert B. Tomer calls this "interface resistance" in his book but does not describe the mechanism because I do not think anybody at the time knew how it happened. It results in a severe loss of transconductance. My guess is that ion poisoning is responsible when the ion trap is not operating.QuoteThe common aluminized phosphors used in oscilloscope CRTs are not susceptible to screen burn except at very high beam currents which explains why I have never seen ones of these CRTs with screen burn from the readout. Contrast them with storage and MCP CRTs where screen burn in the readout area is common.

author: Cyberdragon
author_rank: Super Contributor
timestamp: June 08, 2020, 09:25:30 pm
content: OLED displays can also suffer burn-in (it's a problem with TVs).

author: David Hess
author_rank: Super Contributor
timestamp: June 08, 2020, 11:49:14 pm
content: Low voltage phosphors are also more delicate which becomes a problem in plasma and field emission displays. This might also apply to oscilloscope CRTs which lack post deflection acceleration but there are so few of them that I am not sure. I think CRTs with MCP image amplification also have to use low voltage phosphors but in that case, the MCP itself wears out with use so it may not matter. I am not sure where storage displays fit here although they operate with lower acceleration voltages.

author: Krotow
author_rank: Regular Contributor
timestamp: June 09, 2020, 10:02:25 pm
content: Quote from: Labrat101 on June 06, 2020, 02:26:46 pmActually I seen burn-in lines on at least two laptop LCD screens. My old workplace in nineties had two laptops with Intel 386 and 486 CPUs and LCD screens, made circa 1992 and 1994 by Compaq and probably Toshiba. We used them for inventory accounting and customs declaration preparing. Both programs used forms with distinct white line frames. Also laptops worked without any power save attempts (who need power save when computer is (mostly) always is plugged in wall). During 6 years white frames burned in screens so well that became visible when laptops was turned off. Go figure, why it happened.

author: HwAoRrDk
author_rank: Super Contributor
timestamp: June 09, 2020, 10:29:27 pm
content: Quote from: Cyberdragon on June 08, 2020, 09:25:30 pmYes. My previous smartphone had an OLED screen and had noticeable burn-in after 5 years. The screen had a slight yellow tint to it, with the exception of the Android status bar area at the top of the screen; that area had a black background, so did not suffer from the burn-in. The yellow tint was only noticeable when displaying a white background full-screen - there would be a brighter, whiter strip at the top of the screen - so I wasn't bothered by it, but was disappointed that the OLED display had degraded after a relatively short time.

author: james_s
author_rank: Super Contributor
timestamp: June 10, 2020, 01:00:30 am
content: Quote from: Krotow on June 09, 2020, 10:02:25 pmI don't know that I'd call it "burn-in" though. It's not the same mechanism as worn out phosphors, it's liquid crystals that get stuck and stop responding for some reason. Not sure of the actual mechanism, electrolysis perhaps from less than perfect drive electronics?

author: vk6zgo
author_rank: Super Contributor
timestamp: June 10, 2020, 04:18:47 am
content: Quote from: David Hess on June 08, 2020, 12:30:05 pmThe so-called "ion trap" used in earlier TV CRTs doesn't trap anything!Before such devices, CRTs suffered from "ion burn", where a small circular burn appeared at the centre of the tube over time---- it looked uncannily like a cigarette burn!Along with the desired electrons, cathodes emitnegativeions, which are also attracted to the screen due to its high positive potential.They are not deflected by the magnetic deflection systems used in TV tubes, so always impact the phosphor in the same spot.Although they travel slower than electrons, they are much more massive, & over time, damage the phosphor.(In the case of ordinary vacuum tubes, the anode is mechanically rugged, & no damage is done.)To solve this problem, CRT manufacturers positioned electron guns so that they were "pointed" off screen.To get the electron beam centred, they used a fixed magnet to deflect it back "in line".The negative ions were not so deflected, & continued on their way, finally harmlessly impacting upon the inside of the glass envelope.There remained one other problem---- when the TV was turned off, the desired electron beam was now undeflected, the cathode was still hot, & EHT was still present, resulting in an intense electron beam hitting the centre of the tube.This only happened at turn off, & took a lot longer to show ill effects than ion burn, but would show eventually.This was prevented by the use of a "spot swallower" which opened the cathode connection at turn off.All this technology cost money, adding to the final price of TV set, but aluminised screens swept away both problems "in one fell swoop".The only mechanism by which ions could damage the cathode, as far as I can see, would be if the grid was biased well negative of the cathode, where the ions, once emitted, would return to the cathode which is now the more positive tube element.Positiveions are not present in any significant numbers in the high vacuum of a CRT.Leaving a CRT or any tube on heaters/filaments only on for a long time while not in use, expends lifetime "hours" as the emitting material has a limted service life before emission starts to fall.That said, older Radio & TV Broadcasting transmitters using all tube construction commonly had standard "warm up" times of around 10-15 minutes.This was mainly due to the need to fully prepare mercury vapor rectifiers for use.All the other tubes shared this time interval, with no effect upon their life times.OK, that is not quite the condition you referred to, which would be with all the other elements powered as normal, but the grid biased to cut the tube off.TV sync generators happily operated multiple bistables using 12AT7s or similar, with, at any time, one triode of each pair in cutoff.They also were used in monostables where "one triode in cutoff" would be for more extended periods.This would be similar to your suggested "data" use.Again not quite the use case you mentioned.Quote

author: David Hess
author_rank: Super Contributor
timestamp: June 10, 2020, 07:50:20 pm
content: One of the old Tektronix documents discusses their CRT design history and mentioned the issues with ions and how they were handled. I recall reading that the aluminized screens of later oscilloscopes catch and hold them.One interesting thing I noticed is that old oscilloscopes which have been in storage for 10 years or more have a display which brightens and sharpens over an operating time of days. I first noticed this in my 7603 when I accidentally left it running for a week because being silent, I did not notice that it was on.

author: TimFox
author_rank: Super Contributor
timestamp: June 10, 2020, 08:49:24 pm
content: As a teaching assistant in the Physics department in 1971, we had to ride herd on the students using Tektronix 541 oscilloscopes, since leaving the intensity up (in auto mode) with no input could easily burn a horizontal line on the CRT from the stationary trace along the center line of the display.

author: james_s
author_rank: Super Contributor
timestamp: June 11, 2020, 02:42:23 am
content: Quote from: David Hess on June 10, 2020, 07:50:20 pmI think it cleans up the cathode to be used, impurities are driven out and it "wakes up". Nixie tubes that have sat for a long time often have cathodes that don't fully illuminate but they come back after running for a while.