TEK 2465B Intensity Question - Page 1
Forum section: electronics / testgear

author: George_Race
author_rank: Regular Contributor
timestamp: August 15, 2015, 11:53:40 am
content: I have both a 2445B and a 2465B Tektronix scope.The 2445B has great intensity control from dim to very bright, even at it's fastest sweep speed.On the other hand the 2465B starts becoming dimmer anytime you get the sweep speed above 500ns. By the time you get to 100ns there is very little change in brightness, when you adjust the intensity control. At 50ns and above, the intensity control had almost no change in intensity through most of it's range. Goes from nothing to dim in the first quarter of a turn and then there is no change during the rest of the rotation.I am trying to find the relationship between sweep speed and intensity. I know that the higher the sweep speed the more beam current you need to retain an even brightness level. Seems that there must be some kind of a relationship between the Z Axis beam current and the sweep speed, but so far I have not been able to figure out what that circuitry is.I am going to dig into the "Theory Of Operation" and see if I can find where this all comes together, circuit wise, and go from there.If anyone has any suggestions, as to where to start, or what may be causing this situation, please share your thoughts, it will be most helpful.

author: tautech
author_rank: Super Contributor
timestamp: August 15, 2015, 02:17:01 pm
content: Download theTek troubleshooting guidefrom the Repair board links in the first post by me or you should be able to find it with a Google search on Sphere's Tek parts website.IIRC there is a fault finding flow chart for common faults.The Intensity area of CRT's circuitry is under a fair amount of stress and components often drift from their nominal values. Check high value resistors and pots in particular.

author: George_Race
author_rank: Regular Contributor
timestamp: August 16, 2015, 01:08:46 am
content: Thanks for the link and suggestion. Really no help there either.I have a lot of intensity at slow sweep speeds, it seems to loose control of brightness at the higher speeds.I am still making tests around the Z axis voltage control area.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: August 16, 2015, 03:16:17 am
content: George,You're not in X10 mode, by chance? The sweep width would be about 50" wide, and will be much dimmer...

author: George_Race
author_rank: Regular Contributor
timestamp: August 16, 2015, 11:20:22 am
content: Nope, if I am looking at a 150 MHz signal, and go to 10X, the beam is so dim you just about can't see it at all.Need to find some time to do some more testing, have been busy and not been able to get back to it.

author: tautech
author_rank: Super Contributor
timestamp: August 16, 2015, 09:09:03 pm
content: Quote from: George_Race on August 16, 2015, 11:20:22 amIn CRO's that I have repaired there is normally an internal adjustment and process to set minimum trace intensity.Usually it describes adjustment so that the front panel intensity control can dim the trace unitil it just dissappears at the minimum front panel setting. When adjusted so internally you should have sufficent maximum ajustment available to show a good trace over the full range of timebase settings and in the delayed timebase modes where additional intensity is commonly required.This should be all outlined in the adjustment procedures in the service manual.If the required intensity cannot be obtained by internal adjustment you'll need to work through the internal PSU and HV voltage checks.

author: George_Race
author_rank: Regular Contributor
timestamp: August 17, 2015, 10:38:53 am
content: Thanks for the suggestion on setting maximum brightness.I have gone through the complete set of CRO adjustments and everything worked as expected and described by the service document.The outcome is better than it was, before the adjustments, but still not nearly as bright as my other scope, the 2445B that is a lesser bandwidth model.I have it all back in the case and on the test bench, will see how it works out under some actual conditions.I just wish it was brighter,George

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: August 17, 2015, 04:18:02 pm
content: George,Have you pulled up the screen to report actual on hours on the 2 scopes? It would be of interest to compare.