TEK2213 weird horizontal sweep issue - Page 1
Forum section: electronics / repair

author: tkamiya
author_rank: Super Contributor
timestamp: June 02, 2018, 08:32:32 pm
content: I have a Tektronix 2213 60Mhz 2 channel scope with really weird horizontal sweep issue. Sweep works fine except on following settings:0.5, 0.2, 0.1 seconds : No sweep at all50 milli-seconds: No sweep at all20 milli-seconds: Sweep half way and slowly GOES BACK! (and never comes back)0.5 milli-seconds: No sweep0.2 milli-seconds: Sweep half way and slowly goes back (and never comes back)5 micro-seconds: No sweep2 micro-seconds: Sweep some and goes back (and never comes back)It's obvious there IS a pattern. With this, it looks like either a rotary switch or register bank issue, but I cannot find any faults. I've been looking at circuit diagrams and physical tests, but switching circuit looks fine. Anyone have ANY ideas? I sure don't have any left....

author: tautech
author_rank: Super Contributor
timestamp: June 02, 2018, 11:40:00 pm
content: Take a step back and think what is a sweep.Just a ramp waveform at various frequencies WRT the timebase setting.Go looking with another scope for the ramp.Start at the horizontal plates is you must and work backwards.Good luck.

author: tkamiya
author_rank: Super Contributor
timestamp: June 03, 2018, 06:31:22 am
content: Right. I know that.Right at the output of saw tooth generator, it "flat-lines" when there is no trace. Since it works fine for rest of the timing rate, I it leaves register bank or rotary switch, which I can't find any fault. I must be missing something obvious.

author: tautech
author_rank: Super Contributor
timestamp: June 03, 2018, 08:04:48 am
content: Quote from: tkamiya on June 03, 2018, 06:31:22 amOk, presuming you've done all the PSU checks etc, let's work with this:http://w140.com/tektronix_2213_service.pdfP180 of 224A12 Attenuator/Sweep boardThere's some voltages listed plus TP8.What are you getting all around there ?

author: wn1fju
author_rank: Frequent Contributor
timestamp: June 03, 2018, 04:04:43 pm
content: I feel your pain! Are you sure you have thoroughly checked the rotary cam switch? It is very tedious, but you can do it with an ohmmeterwith the scope powered off to verify the cam is acting on ALL contacts properly. I have seen and repaired many instances of Tek cam switchesand have seen things like 1) contacts fused shut, 2) dirty (hence open) contacts, 3) switches that have sections totally rotated out of position,and other maladies.And, of course, for horizontal sweeps, you should make sure all of the timing resistors are OK. I've had instances of open resistors, butthese tend just to make the sweep have the wrong timing, not kill it completely.Good luck. I'm interested in reading about the final outcome.

author: tkamiya
author_rank: Super Contributor
timestamp: June 04, 2018, 03:24:59 am
content: At this point, I'm not sure of anything. I checked the rotary switch for combinations I thought were relevant. But the tests weren't exhaustive. Tests for register banks were pretty exhaustive. I'm nearly sure I covered it all.I was flabbergasted when a trace came out, paused for a bit, and went back in!

author: tkamiya
author_rank: Super Contributor
timestamp: June 04, 2018, 10:50:10 pm
content: I found some issues with the rotary switch. In order for it to NOT outsmart me, I labeled each pins and checked with continuity tester. There are pin pairs that never make contact and according to the schematic, it matches with scan rates having problems.Now, the question is, what do I do about it? I don't have sufficient de-soldering equipment to take the switch off without causing damage. So board swap is probably the only option.It is a TEK 2213 scope, Attenuator/Sweep board,GB-7344-02 A12I wonder if anyone here have one to part with?

author: tautech
author_rank: Super Contributor
timestamp: June 04, 2018, 11:14:47 pm
content: Quote from: tkamiya on June 04, 2018, 10:50:10 pmIf you look at the A12 board on P203 and 204, there's a lot of calibration adjustments that are specific to that boardand yourscope. A12 replacement would require you to check all those adjustments to know if your scope was accurate enough to use. Do you have the gear to perform those checks ?If not you should look hard at other avenues to repair this scope.

author: wn1fju
author_rank: Frequent Contributor
timestamp: June 05, 2018, 01:19:06 pm
content: I apologize for my earlier reply where I discussed cam switches. It looks like the 2213 does indeed have a rotary switch, not the usual camtypes found in earlier Tek scopes.Nonetheless, at this point, if you are actually considering a board replacement, you have nothing to lose by flooding the switch in alcohol andexercising it a few dozen times. After the alcohol dries out (a couple of hours), see what you get.If I recall, I had a 2213 years ago that also had a marginal timebase switch. Not as bad as yours, just noisy so that the timebase would jumparound if the knob was touched lightly. The alcohol treatment cured it.

author: tkamiya
author_rank: Super Contributor
timestamp: June 05, 2018, 01:56:35 pm
content: I'm ahead of you there! I did flood it with Deoxit and that made no difference. I'm thinking how I can take this switch off the board and apart. Since I got this scope for free, and I already have too many, there is really nothing to lose. Or, do something weird and remake the switch function with relays and a small logic board. I do have a fairly well equipped lab but not enough to calibrate with any degree of certainty.

author: tkamiya
author_rank: Super Contributor
timestamp: June 06, 2018, 03:00:35 pm
content: With finding that the rotary switch is the culprit, and having no way to take it apart or source the replacement, I ended up shelving the unit for later review.I can think of doing something like using a small computer to actuate relays or some other "heroic measures" but that kind of fix will exceed the value of equipment. Besides, I want my Tektronix the way company original designed it.Thanks everyone for assistance.