Marks on Keysight scope screen - Page 1
Forum section: electronics / repair

author: bob_1
author_rank: Newbie
timestamp: August 13, 2025, 06:53:05 pm
content: Hi.I bought this scope new years ago. I rarely use it. When I finally went to clean the screen, these 'marks', which I think were always there became very visible.I cleaned the screen with a very soft micro fiber cloth slightly wet with water. Whatever the marks are, they appear to be under the front surface.I'm looking for info/advice as to what these marks could be, and suggestions how to remove them. I assume that I'll have to disassemble the scope and hopefully cleaned from the inside.I contacted Keysight, and after a long process of lost emails and others things, they said the scope could be 'core' repaired for nearly the full cost of the original scope purchase price.I really want to clear the screen of these marks, as they are much more distracting while the scope is in use than the photos show.Thanks.

author: metrologist
author_rank: Super Contributor
timestamp: August 13, 2025, 09:22:26 pm
content: Most unfortunate!I have a VNA that looks like light mold between the glass. Your shapes seem too geometric to be that.

author: J-R
author_rank: Super Contributor
timestamp: August 13, 2025, 11:56:46 pm
content: Any chance it's just the screen protection film from the factory? I don't see the tell-tale tab, but I'm still curious.Looking at mine, it does seem clear that the LCD is a separate part behind the front glass. Can you take another photo at an angle with the unit powered on? This should help establish whether this problem is the front glass or the LCD panel.

author: bob_1
author_rank: Newbie
timestamp: August 14, 2025, 03:58:01 am
content: Best as I can tell, the 'marks' are not on the surface of the display facing the user. Perhaps on the backside of that same front panel as they look close to the front surface, but not on the front surface.I cannot see any screen protector.

author: chilternview
author_rank: Frequent Contributor
timestamp: August 14, 2025, 08:12:30 am
content: They look like finger marks to me. Have you tried opening up the scope - there is probably a plastic screen protector in from of the screen, maybe this has dust or dirt on the backside?

author: J-R
author_rank: Super Contributor
timestamp: August 14, 2025, 08:52:32 am
content: Since the two new photos are taken at opposite angles, I expected the alignment of the marks and the LCD display to have changed if it was the front glass.It's hard to say for sure, but it actually seems like it's on the face of the LCD panel under the glass.Either way, I think time to open it up, although I suppose you could hit it with some window/glass cleaner first.

author: wraper
author_rank: Unknown
timestamp: August 14, 2025, 09:01:35 am
content: IMHO It's protective piece of plastic in front of the screen is touching the LCD itself. Which in case of glossy LCD surface, it will cause such effect. Depending on construction you may need to put some washers under screen mounting points, or remove a little bit of plastic from them to increase the distance between the LCD and the protective plastic a little bit.

author: J-R
author_rank: Super Contributor
timestamp: August 14, 2025, 10:03:03 am
content: On these units the glass is not touching the LCD. There is actually quite a bit of space between them.Dave tears one down here:The glass is surprisingly thick. It is kept away from the LCD by the metal frame.I inspected mine and it has a similar issue, although a completely different pattern, more like some fine lines and random specks. It's not noticeable except with a flashlight. I think this could be something that got on the LCD prior to assembly and is now turning into something else due to age.Looks like I have a project for the weekend...

author: bob_1
author_rank: Newbie
timestamp: August 14, 2025, 02:47:03 pm
content: Thanks for the link to Dave's video. Will be helpful in the disassembly.Taking the front panel off the LCD assembly does look a little scary though.

author: TheSteve
author_rank: Unknown
timestamp: August 14, 2025, 03:47:12 pm
content: I have seen this before. The fix is to remove the LCD unit and then take the front glass off so you can clean both the LCD and glass. It is held on with double sided tape/adhesive. You can use dental floss or fishing line as a saw to slowly cut it away. It only takes a few minutes. Once both are clean you can use some thin strips of 3M double sized tape to attach the glass back to the LCD and it will be as good as new.

author: Sorama
author_rank: Frequent Contributor
timestamp: August 14, 2025, 03:49:32 pm
content: I too think this is condensation with mold between two parts of the display.

author: wraper
author_rank: Unknown
timestamp: August 14, 2025, 04:39:45 pm
content: You don't need any dirt between them. It's the same visual effect as when you put a screen protector on a smartphone screen and get some air bubbles underneath.

author: bob_1
author_rank: Newbie
timestamp: August 14, 2025, 05:03:41 pm
content: You can use dental floss or fishing line as a saw to slowly cut it away.Per the red arrows in the picture?

author: TheSteve
author_rank: Unknown
timestamp: August 14, 2025, 05:25:44 pm
content: Yes, that is where the adhesive is holding the glass to the LCD.

author: wraper
author_rank: Unknown
timestamp: August 14, 2025, 06:15:53 pm
content: Looking on the picture, no wonder there is such an issue. Whoever designed this had no clue and used super thin adhesive tape. This sort of works OK only when using matte LCD as there is always a small air gap even if they touch together. However matte sucks when put behind a window due to excessive reflections between the window and LCD surface. 15-20 years ago when attaching LCD and screen window with a transparent adhesive was not a thing yet, phone manufacturers used about 1-1.5mm thick adhesive or non-adhesive gasket between them.

author: bob_1
author_rank: Newbie
timestamp: August 14, 2025, 06:40:53 pm
content: Thanks!

author: TheSteve
author_rank: Unknown
timestamp: August 14, 2025, 07:04:33 pm
content: I've only seen this issue on one out of many scopes I've worked on. Seems to be an out-gassing issue from something - maybe the original LCD, or even the tape itself? Perhaps it only happens if it was stored in a hot or maybe humid environment. Or it was just something not quite right for a small batch of production. No matter the cause it will clean off with alcohol or lens cleaner.

author: wraper
author_rank: Unknown
timestamp: August 14, 2025, 08:24:23 pm
content: Quote from: bob_1 on August 14, 2025, 05:03:41 pmThere is another safer method. Put it in the oven and heat it to 60-70oC. If it's a regular baking oven, I'd verify temperature with thermocouple first as higher temperature may damage LCD. Then once out of the oven, quickly pry with a plastic spudger from the corner and slowly lift it off, you may need to go around with a spudger if adhesive still holds it strong enough.