Blur on trace - Page 1
Forum section: electronics / testgear

author: Axtman
author_rank: Regular Contributor
timestamp: February 19, 2014, 06:31:52 am
content: I have an old Tektronix 465B that has some "fuzz" on the trace. Is there a way to make a bright sharp trace? Is this blur a symptom of an aging CRT? The photo below is not my scope but typical of what my trace looks like. Is this called "overshoot? Thanks!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 19, 2014, 06:37:02 am
content: Looks like the brightness is cranked waaayyyy past the useful point.Blur can also be caused by noise, anywhere from the input (if not grounded) through the vertical amplifiers.

author: Psi
author_rank: Super Contributor
timestamp: February 19, 2014, 06:38:25 am
content: +1 for Intensity set too highTry crank it down, left knob of the 3 bellow the CRT on the left.

author: DC5AJ
author_rank: Unknown
timestamp: February 19, 2014, 12:33:40 pm
content: This behavior is not called overshoot, the other two members said it before, it seems to be the brightness is set to high. Overshoot looks like this for example :

author: PedroDaGr8
author_rank: Super Contributor
timestamp: February 19, 2014, 03:58:43 pm
content: Quote from: DC5AJ on February 19, 2014, 12:33:40 pmTo clarify a bit, the image he shows should be a square wave, but it's overshooting the leading edge badly. That's what overshoot is. It has nothing to do with intensity or blurriness.Your image just shows intensity turned too high. As a result you can see stray electrons from the beam/noise.Sent from my EVO using Tapatalk

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 19, 2014, 07:01:05 pm
content: I think I barely make out the white mark on the dial... should show up better after clean up.

author: grumpydoc
author_rank: Super Contributor
timestamp: February 19, 2014, 07:17:01 pm
content: QuoteA minor point, but you have a 465, not a 465BThere are cosmetic differences and the "B" can show the delayed time base and the main time base together on screen (well, alternating as it happens but the effect is that you can see both).It's still a perfectly good 'scope to ownAs others have said, turn the intensity knob down.

author: Axtman
author_rank: Regular Contributor
timestamp: February 19, 2014, 07:29:48 pm
content: That picture is actually not my scope but a picture that I found on the internet show the issue. If I turn down the intensity the "fuzz" goes away but the trace gets dim and almost disappears. Is there a way to get a bright trace without all the fuzz?

author: tautech
author_rank: Super Contributor
timestamp: February 19, 2014, 08:11:56 pm
content: It is likely your OLD scope componentry is getting tired and/or has drifted in its settings. Some components may need to be replaced or updated.I suspect the CRT circuitry needs adjustment as per Service manual setup. Manual will have listed the gear you need. Once done properly you should have a crisp trace again.

author: grumpydoc
author_rank: Super Contributor
timestamp: February 19, 2014, 08:14:53 pm
content: QuoteOr at least pictures of yourown'scope - it's a bit hard to tell you what's wrong with yours based on a photo of someone else'sCRTs have a couple of failure modes.One common one is "low emissions" caused by a worn out cathode or cathode poisoning - often this manifests itself as a "dual peak" in the brightness as the intensity is turned up the trace first brightens, then dims, then possible brightens again.Another is the tube leaks and air gets in - this causes general low brightness and sometimes a milky discolouration around the neck of the tube.Now, on to yours. Set the input coupling to GND, turn the intensity control fully anticlockwise then clockwise until you have a reasonably bright trace and adjust the focus for the best line.Can you get a sharp trace?