Is this screen burn in ? - Page 1
Forum section: electronics / testgear

author: JeLo
author_rank: Contributor
timestamp: April 11, 2016, 10:39:30 pm
content: Hi, there. I got my first oscilloscope second hand on eBay and apparently so far it works (still learning though...) but one thing's bugging me.With the unit off there is a darker relatively small (but not tiny) area to the right of the screen, almost not noticeable when it's on. I actually found one on eBay that seems to be showing the same problem but this one is much more severe. It's here:http://www.ebay.com/itm/Tektronix-TAS485-Analog-Oscilloscope-TESTED-GOOD-/291487548685Can someone please confirm ? The seller told me it's just the perspex protection plate over the CRT screen that needs cleaning, which obviously is not the case as when I wiggle it a bit (the front crt protection) the darker area doesn't move with it. Like I said I can live with it as it's not as bad but it sickens people sell stuff like this, I really didn't notice it at first when inspecting the auction but looking back at some pictures it's there, and only now did a search on google and burn in seems to be the cause...By the way, if it's screen burn, I don't understand how it can be over such a big area, I mean waves are normally just a line...Thanks all and great forum

author: JeLo
author_rank: Contributor
timestamp: April 11, 2016, 11:05:20 pm
content: Hmm maybe it's not screen burn, found already two similar ones from the same series but lower in the line, that have the same problem.Here:http://www.ebay.com/itm/Tektronix-TAS465-100-MHz-Two-Channel-Oscilloscope-TAS-465-/361529354000?hash=item542cd42710:g:cMsAAOSwz2lXBliiAnd here:http://www.ebay.com/itm/Tektronix-TAS475-Analog-Oscilloscope-4-Channel-100MHz-/351682437218?hash=item51e1e82062:g:W38AAOSwKtVWzT1mSeems to be always on the right (well, maybe some have on the left, still haven't seen one though...).I'd like to know if that's repairable...Cheers

author: edpalmer42
author_rank: Super Contributor
timestamp: April 11, 2016, 11:08:39 pm
content: If you're referring to that dark patch on the right side of the screen, no, that's not normal screen burn. Screen burn is when the same image sits on the screen for a long time. Often it's things like menus, grids, labels, etc. Here's a good example of screen burn.http://www.ebay.com/itm/231098337079We'd have to see a picture of what you have to even guess what it might be. It could be nothing more than an uneven layer of fine dust on the face of the CRT. I've seen that before. Even if the CRT looks okay, after you clean it you realize that it was filthy!Ed

author: JeLo
author_rank: Contributor
timestamp: April 11, 2016, 11:29:41 pm
content: Thanks a lot for your reply. Yes that's what I meant. Still, how come dust only accumulates on one side and one area ? For a better photo, if you click on the picture of the first auction I posted (to get a super sized pic) and then click on the arrow to the left you get a second picture that I don't think I can take a picture of mine that would be more revealing. The one after that one is even better.

author: wraper
author_rank: Unknown
timestamp: April 11, 2016, 11:37:40 pm
content: Might be just dust/dirt under the screen protector. I see it happening at may work in accelerated fashion, corners became opaque. Need to disassemble the screen of particular devices for cleaning once in a few years. They are used for analyzing coal powder samples, so that stuff flying in the air gets inside.

author: Andy Watson
author_rank: Super Contributor
timestamp: April 12, 2016, 12:21:56 am
content: Quote from: JeLo on April 11, 2016, 11:29:41 pmI agree, it does not look like screen burn. Is there a fan in these scopes? - That is sucking air (and dust) through the button holes on the front panel and then across the screen ?

author: med6753
author_rank: Super Contributor
timestamp: April 12, 2016, 12:46:06 am
content: I agree with the group. It looks like dust/dirt on the face of the CRT. That used to happen often on vintage TV's that had a separate glass front bezel. The rubber seal would age and become brittle and cause gaps.The fun part is you may have to disassemble and pull the CRT to clean it.

author: edpalmer42
author_rank: Super Contributor
timestamp: April 12, 2016, 03:09:36 am
content: Quote from: JeLo on April 11, 2016, 11:29:41 pmWhy on one side? Because that's where the button holes are. Why only in one area? You'd have to disassemble the scope and look for gaps or spaces in that area. Don't forget that the face of a CRT has a significant static charge. The charge will attract dust, but only the smallest particles will make it through to the screen. If there's a fan that's blowing air out, that means that it will be sucking in air everywhere which will just add to the problem. I have a portable spectrum analyzer that was exactly the same. The dust was on the right hand side of the screen. And there'snofan in it.You might be able to use a flashlight to illuminate the 'dust' and tell if it's on the inside or outside of the CRT. Try with the power on and off. Try straight on and at a very shallow angle (almost parallel with the front of the scope). Some type of magnifier might help.Ed

author: Brumby
author_rank: Unknown
timestamp: April 12, 2016, 03:47:38 am
content: While the discolouration is the sort of thing I would expect from screen burn - that's NOT the sort of patterning I would expect. It would take a rather complex and erratic waveform at extreme brightness over a long time to do anything like that ... and I just can't imagine it.There's also the (extremely remote) possibility that something bizarre has happened and the phosphor is indeed damaged, but what that could be I don't know.Can't say I've had any experience with dirt/dust inside my scope - it's only been used in relatively clean environments, but for your sake, I hope that's all the problem is.

author: Fraser
author_rank: Super Contributor
timestamp: April 12, 2016, 11:04:15 am
content: I have seen this a lot on spectrum analyser that have high hours on them. Convection currents, static electricity and a non clean room working environment causes the dirt to accumulate in certain areas of the CRT and it's protective face plate. Just clean with soapy water on a damp cloth and it comes off easily. As others have stated, getting to the rear of the face plate can be the challenge. My Spectrum Analysers have an easily removed faceplate bezell held on by 4 screws. Some equipment requires the removal of the whole front panel plastics though.Fraser

author: JeLo
author_rank: Contributor
timestamp: April 12, 2016, 12:30:43 pm
content: Again, thx all for the replies.Yes, the unit does have a fan! That probably makes it even more likely that it's dust/dirt particles of where it was used before.Funny thing, I noticed some of the units selling on eBay that have this sell for a much lower price because people don't know what it is.

author: JeLo
author_rank: Contributor
timestamp: April 12, 2016, 12:34:07 pm
content: BTW, IIRC there is another layer of glass internally so it's not like the dirt is right on top of the phosphor. Which means I can be lazy and clean it off later, I want to have some fun with it first before opening it, after all I bought it to help repair other stuff...But I would like you guys confirmation on this..

author: edpalmer42
author_rank: Super Contributor
timestamp: April 12, 2016, 02:00:10 pm
content: It apparently doesn't affect the operation of the scope. Whatever it is, whether dust, screen burn, or something else, it's been there for a while. So I guess it doesn't really matter when you get around to checking it out.Ed

author: Fraser
author_rank: Super Contributor
timestamp: April 12, 2016, 02:27:18 pm
content: Just use it and let it pay for itself for as long as you can tolerate the dirty screen. In the mean time try to find the service manual as that will likely detail screen cleaning and what is required to gain access. Keep searching Google for any references to repairing this or similar models of scope. Such articles sometimes include pictures of disassembly.Me ? I am OCD on dirty screens and would have already dismantled and cleaned the whole thing. Be aware the dirt may be in other parts of the scope that are less tolerant of such, such as EHT circuits and the cooling fan/filters. I would likely also knock out and repaint any case damage as well...... That is getting extreme thoughFraser

author: Brumby
author_rank: Unknown
timestamp: April 12, 2016, 02:32:36 pm
content: Quote from: Fraser on April 12, 2016, 02:27:18 pmI'm not OCD - but I would be very likely to at least have a quick look inside to check out the dust situation. I had an old CRT TV I recently handed down to one of my sons (so he could run his old Nintendo, etc. without lag) - and I pulled the back off and cleaned out the dust. (I also discovered that it had a Samsung picture tube - in a DSE branded set.)This was for a set that I'd had since new, so I'd be a little more apprehensive for a used bit of kit - until checked out.