tektronix oscilloscope with blurry corners? - Page 1
Forum section: electronics / repair

author: coppercone2
author_rank: Super Contributor
timestamp: March 18, 2021, 01:44:02 am
content: So I got a working tektronix 500MHz CRT scope but the problem it has is that 2 corners are blurry, it looks like someone smeared grease in there, its not on the waveform but it makes the scope look like someone put their thumb in the corner after using vasiline. I checked the test signal on all 4 connectors and it appears fine, it is the type of tektronix with the black and white display with a floppy drive.I will take it apart eventually but i was wondering what the hell is this? I touched the screen to make sure there is no grease there.Most of the display looks good, but normally I am used to seeing like distortion, this just looks like grease. I almost want to take apart the screen assembly to check for grease but since its in opposing corners I figure unless someone was doing something really weird with it, it is some kind of issue with the focus circuit. Is this just how distortion looks like on those early 90's oscilloscopes? It is uncanny.Or, can grease some how accumulate in there and settle in the corners?I would not be surprised if there is bad capacitors in there from experience with this age of tektronix, but it just looks really weird/confusing.

author: CaptDon
author_rank: Super Contributor
timestamp: March 18, 2021, 01:19:33 pm
content: Is there a bezel between the glass face of the CRT and the viewers side of things?? I have seen dirt and dust be attracted to the space in between and make for poor viewing. Some tektronix C.R.T. circuits had a dynamic focus pincushion correction which will indeed create weird focus issues, good in the corners and crappy in the middle, or the opposite like in your case. Worth investigating.

author: jonpaul
author_rank: Super Contributor
timestamp: March 18, 2021, 03:47:36 pm
content: send photos and scope make/model for better responsej

author: coppercone2
author_rank: Super Contributor
timestamp: March 19, 2021, 01:50:49 am
content: The camera makes everything look a little blurry but look at the 'grease' in the corners, especially visible intop left.I wanna have an idea of what I am in for when I take this apart because I already have other equipment apart and when I take it apart I want to try to fix all the problems in 1 go, meaning ordering capacitors and leaving the equipment open for a long time, so it screws up my work area, since I still have a open 3310B and a 33a sorensen open right now and some new stuff coming in mailTrying to maintain FIFO because I had some of these broken since like 2016 and its just too much so I am trying to force it. Also need to fix a negative voltage problem on my 4 adjustment digit voltage&current source and add a IEC connector to it.. I should not have bought the low noise oscillator but I could not resist and that probobly needs repair and I need to make a graphite wear plate for my pace solder extractor.I do feel like if I got the scope in order first maybe it would make the 3310b easier to trouble shoot, the 1052E was pissing me off... and the freaking horizontal adjustment encoder suddenly became dicky too, and my scopemeter needs serious plastics welding repairs to feel safe on the bench lol, then the front panel on my wavetek 395 broke too and its hung on by duct tape (2 plastic repair jobs), and my shaft repair on the sorensen power supply is not working (something is wrong with the DP8810 acrylic adhesive!, if it would just cure I can give it a wire wrap job and put it back on the shelf), then the lqd-422 needs a new voltage referencemy house feels a little bit like the b52 in the end of doctor strangelove lol, everything is jammed up sparking and blinking

author: bdunham7
author_rank: Super Contributor
timestamp: March 19, 2021, 02:06:13 am
content: Have you tried a degaussing?Does it have a short(er) CRT with a flat screen? It might have the astigmatism issues that CaptDon referred to.

author: coppercone2
author_rank: Super Contributor
timestamp: March 19, 2021, 02:11:50 am
content: it is a tds540, same screen as a awg2020 i think, all the tektronix that look like that have the display module iircMy experience with the awg2020 is that the display was totally fucked up and leaking and the design was horrible with power resistors surrounding capacitors like fire wood around a dutch oven , I just replaced the entire assembly because it was like trying to clean charnobyl , if i recall I was more pleased with the newer revision of the PCB then what my unit had after a quick visual inspection (it had like 5 revisions if i recall)What is a good way to degauss this? harddrive Magnet on a spade drill maybe?Maybe I will try to fix the sorensen 33-33 since its huge then postpone the other stuff and open this up and get more details if you need model numbers on a CRTif I open any more large objects right now bad things will happen I think

author: coppercone2
author_rank: Super Contributor
timestamp: June 17, 2021, 04:09:24 am
content: the machine has a huge amount of dust accumulated at the corners of the CRT, it must be this way because of the color/graphics choices, because green CRT usually just look dim instead of blurry

author: james_s
author_rank: Super Contributor
timestamp: June 17, 2021, 05:21:38 am
content: Is the TDS540 one of the ones with the NuColor display? Those do have an optical gel between the CRT and the shutter glass. Either way these use a monochrome raster CRT, there should be a focus adjustment on the monitor board, you'll probably find it's a tradeoff between good focus on the center and good focus at the edges.

author: coppercone2
author_rank: Super Contributor
timestamp: June 17, 2021, 05:31:33 am
content: it looks perfect as soon as I wiped down the inside front face of the CRT and the back face of the glass.i don't know what it uses, there is a plane of some kind of coated glass (perhaps EMI or antireflection, its green ish) in front of a bare CRT tube. the dust accumulated on the corners of the CRT and glass for whatever reason, but not so much in the middle (something with electrostatics).