Tek 2211 "stuck" in XY mode - Page 1
Forum section: electronics / repair

author: Alex8
author_rank: Newbie
timestamp: November 29, 2024, 10:29:56 pm
content: I recently got my hands on a Tektronix 2211 DSO, worked perfectly except for the Ch.1 V/div dial that was a bit sticky and slow (worked fine though), so i pulled the scope apart just enough to spray a copious amount of contact cleaner into all the pots and rotary switches while working it back and forward vigorously, i also did this for Ch.2 as well as the timebase dial, which is the issue at hand. For some reason the scope seems to have decided it likes staying in XY mode (the first setting on the dial), which is clear by the fact that the scope is indeed in XY mode regardless of the dial position (which still turns and clicks freely with no issue) while in the digital acquisition mode which doesn't support XY it works fine except there's no timebase adjustment. The switch looks and feels fine, the shell of the actual switch elements is translucent and i can see the contacts operating just fine, the other odd thing is that whenever i turn the dial over it will sometimes completely randomly make the readout portions of the display fade out and then in again while the waveform remains untouched. I don't dare dig into this thing any more without service documentation which seems to be non-existent, as this is the first time i'm ever cracking open an analog scope. Has anyone experienced a similar issue? Does a service manual for this thing exist? I would appreciate any help, i'm glad to provide photos if needed although i'd like to stress that absolutely nothing looks out of order. Thanks!

author: wn1fju
author_rank: Frequent Contributor
timestamp: November 30, 2024, 12:44:07 pm
content: Service manual athttps://w140.com/tekwiki/wiki/2211You might want to check out the timebase switch with an ohmmeter.Also, when things seem to come and go randomly, suspect loose connections and/or poor solder joints. Do things change when you tap any of the boards?Good luck with the repair. I glanced at the service manual and it seems like a fairly complicated piece of gear.

author: Alex8
author_rank: Newbie
timestamp: November 30, 2024, 01:49:57 pm
content: Thanks, i totally missed the service manual link. Stupidly enough i did not think to simply check the switch with a DMM, but it is also about 3 switches in a row with dozens of positions so that alone is gonna be quite the task, i tried tapping and it didn't help, the solder joints look fine but a kiss with the iron and some flux couldn't hurt i guess. Thanks again for the pointers

author: Alex8
author_rank: Newbie
timestamp: November 30, 2024, 02:21:14 pm
content: So, stupidly enough, it looks like there was a totally random grounding tab that was not seated correctly that was shorting some seemingly random point to ground, shimmying it out of the way seemingly restored the scope to its prior functionality. With that out of the way, i'm now back to the position where i was when i first got the scope, being a bit inexperienced with analog scopes and mostly having used digital ones, is it normal for it to be difficult to get a stable waveform at lower frequencies? for instance, probing anything that's about 50Hz, i cannot get the waveform to both a) be steady on the screen, as in not scroll across the screen and b) not blink/flicker, is this a common thing with analog scopes or should i be investigating further repair. Also, when probing the scope's built in calibration generator (1kHz/500mV square), i notice a strange effect, where even though i can get a steady image on a large section of the timebase options, sometimes the intensity of the waveform will change pretty drastically, for instance between 20us and .2ms the waveform is fairly intense and also flickers regardless of how i twiddle the trigger level and holdoff, below 20us it gradually fades in intensity for each step until .05us where it basically fades out of existence, above .2ms it immediately snaps into a lower (seemingly more reasonable) intensity and stays that way on all settings below on the dial, when the intensity drops for instance it becomes impossible to see the rise and fall of the square wave, which is reasonable at a low intensity although unexpected for the intensity to vary that drastically. I don't necessarily expect much handholding but i would like to know if this is normal/tolerable behavior for an analog scope or wether i should look into further repairs. Thanks

author: wn1fju
author_rank: Frequent Contributor
timestamp: November 30, 2024, 05:32:59 pm
content: It should not be difficult to get a stable trace at low frequencies like 50 Hz. The waveform should be nice and bright, not really flickering. Of course, at very slow timebases (like >1 sec/div), the left side of the screen will start to fade away as the right side is being drawn. But assuming you have a reasonable timebase to show a few cycles, 50 Hz should be crystal clear. One caveat: If the scope is putting text annotations on the screen, however, you may see a slight gap in the waveform since it is alternating between writing the trace and writing the annotation. This occurs in a most analog Tek scopes and is normal.I'm assuming you are in the analog "non-store" mode since the scope will act differently if it is in storage mode. In particular, you mention "scroll across the screen." This is a normal feature at slow timebases while in digital mode, not analog. There is no "scrolling" in analog - the beam simply sweeps across the screen. In digital mode, where the waveform is acquired into memory, the scope is able to draw things on the CRT to make it appear like the waveform is scrolling.As far as the calibration goes, that signal is used to set the proper capacitive compensation on a 10x probe so that the resulting waveform is square without any undershoots or overshoots. But regardless, that waveform should not drop excessively in intensity as the timebase gets faster and faster. It is the case that most analog scopes diminish slightly in intensity at very high frequencies. And that is simply because the beam is sweeping very fast across the phosphors of the CRT, so there is less absorption than at lower sweep rates. But the dropoff in intensity is usually minimal. You might have to turn up the intensity a bit, but not much.It's hard to tell if something is still wrong with your scope or if it is operator error. Appendix A of the operator's manual (obtained from the same Tek Wiki site) gives a step-by-step check of the performance. It's tedious at best, but perhaps worth doing.