IWATSU oscilloscope Cal signal square wave showing as ramped / curved signal - Page 1
Forum section: electronics / repair

author: Michelle
author_rank: Contributor
timestamp: May 01, 2024, 06:40:41 pm
content: Any ideas what could be causing this? Capacitors inside gone bad? Besides this obvious issue, things appear to do what they're supposed to.

author: BreakingOhmsLaw
author_rank: Frequent Contributor
timestamp: May 01, 2024, 08:06:24 pm
content: Looks like you need to adjust your probes to the scope. There's probably a small grub screw somewhere.

author: tggzzz
author_rank: Super Contributor
timestamp: May 01, 2024, 08:21:51 pm
content: Quote from: Michelle on May 01, 2024, 06:40:41 pmYou don't tell us what the signal is, what the probes are, what the scope settings are.Ifthat is a ~1kHz square wave "cal" signal on the scope's front panel, andifyou are using a standard *10 "high" impedance 10Mohm probe, then it is probable that you haven't adjusted the probe's low-frequency response.Such probes will say "for 12-25pF scopes" or similar. Provided the scope's input capacitance is within the stated range, you should be able to fiddle with the probe to get acceptable results. See the probe instructions, or any introductory scope/probe text.If all else fails, that info (and much more) is in the links athttps://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: May 01, 2024, 10:55:01 pm
content: under compensated probe

author: BrokenYugo
author_rank: Super Contributor
timestamp: May 01, 2024, 11:05:44 pm
content: Likely no issue, just more setup work to do.I've seen some that have the adjust screw on the BNC end, but the basic procedure holds for more or less every scope built since the 70s.

author: Zenith
author_rank: Frequent Contributor
timestamp: May 01, 2024, 11:37:39 pm
content: Too many unknowns here.Are we looking at a signal from a 10x probe connected to the calibrator pin?If so, it could be a badly compensated probe, it could be a good probe that has the wrong capacitance range for the scope, or it could be a faulty probe. It might be a fault in the scope. Try a known good probe and adjust it with the tool provided.Or are we looking at a signal from a signal generator with appropriate termination?

author: Michelle
author_rank: Contributor
timestamp: May 02, 2024, 01:04:28 am
content: It's a Lecroy 350mhz 10:1 10Mohm 14pf probe (yes I tried adjusting the screw, changing it from what is pictured makes the sweep worse) hooked up to the oscilloscope's CAL tab, with the scope set to the settings the user manual suggests for calibration. It is supposed to be a square wave. I have calibrated an oscilloscope before and understand how it is supposed to work and look.The oscilloscope is an Iwatsu 5705, I believe, and didn't come with any probes; this is just a probe I had. I was told the oscilloscope used to work but it has been sitting for a few years and been moved a couple times. I don't know the spec on the original probe besides I believe it's 10Mohm , I just assumed this one would work.https://probemaster.com/4900-oscilloscope-probe-basic-kit-150-300-mhz/This (4901-2) is supposed to be a compatible probe to the original iwatsu ss-0060; it's not clear to me how different this is than the lecroy PP002 I tried is.And yes the probe works fine on another oscilloscope give me a break here guys...

author: bdunham7
author_rank: Super Contributor
timestamp: May 02, 2024, 03:31:11 am
content: Quote from: Michelle on May 02, 2024, 01:04:28 amThe Probemaster 4901 has a compensation range of 10-50pF, meaning it will work on scopes with up to 50pF input capacitance. IDK what the input capacitance is on your Iwatsu, but it may be higher than the maximum compensation available with that LeCroy probe. Or, it may be broken.

author: Michelle
author_rank: Contributor
timestamp: May 02, 2024, 03:58:58 am
content: Is there anything I can try to troubleshoot it short of buying a different probe to try?I have other probes but they are the same or less capacitance.The thing that makes me wonder is you would think the signal would get better to the farthest end of the adjustment range but it gets worse looking and seems closest to square (not at all) towards the middle of the adjustment (the le croy probe)

author: DimitriP
author_rank: Super Contributor
timestamp: May 02, 2024, 04:22:25 am
content: How about a direct connection from the calibrator output to CH1 ( try ch2 as well) using a straight wire?

author: jonpaul
author_rank: Super Contributor
timestamp: May 02, 2024, 04:34:56 am
content: Take a wireConnect scope CH 1 input DIRECT to CAL outIf its sq wave, bad probe or uncompensated probe.See Tektronix Circuits concepts books at W140, BAMA archive,"Oscilloscope Probe Circuits"and "Oscilloscope Probe Measurements"Bon chanceJon

author: 2N3055
author_rank: Super Contributor
timestamp: May 02, 2024, 06:27:29 am
content: Quote from: bdunham7 on May 02, 2024, 03:31:11 amThat Iwatsu has 32pf±2pF input capacitance. That fast LeCroy 14pF probe probably cannot be compensated.

author: Michelle
author_rank: Contributor
timestamp: May 02, 2024, 01:36:45 pm
content: Thanks you guys. I will try wiring directly. I also didn't see the spec for the Iwatsu capacitance so thank you for finding that!

author: bdunham7
author_rank: Super Contributor
timestamp: May 02, 2024, 01:38:13 pm
content: Quote from: Michelle on May 02, 2024, 03:58:58 amFirst you might adjust the horizontal sweep so there were fewer cycles on the screen. Then, as suggested, use a wire or 1X probe or BNC-to-alligator clip adapter to connect directly to the calibrator output and see what you have. I'm presuming you do not have another scope handy for testing, but you mentioned you have other probes? Why not try one?

author: Michelle
author_rank: Contributor
timestamp: May 02, 2024, 01:43:35 pm
content: I don't know why you guys think I don't have another oscilloscope lol. Is it the female name?I've just never messed with an analog scope before is all, and I'm used to using newer stuff that "just works"Like I said my other probes are similar (Agilent 12pf) and I know the lecroy probe works fine.Anyway I just tried a wire going directly from the connector to the CAL output and the waveform looks the same so I guess the problem is with the oscilloscope itself.

author: 2N3055
author_rank: Super Contributor
timestamp: May 02, 2024, 01:49:06 pm
content: Quote from: Michelle on May 02, 2024, 01:43:35 pmNo, not because of the name (I didn't even notice it to be frank). We have many non-male members here that are very good engineers...We presumed no other scope, because first thing I would try would be to test the signal with another (good, working) scope and probe.

author: Michelle
author_rank: Contributor
timestamp: May 02, 2024, 01:51:20 pm
content: I did use an arduino to generate a square wave and got the same result which I neglected to mention.Also I was about to shut it down but I changed the volts/div knob and suddenly the signal changed from the swept wave to a square wave (with a plain wire connected)! Now I'm wondering what's actually going on here. I need to get more Electonics cleaner and try cleaning it out possibly.Anyway like I said I already know this is a good probe so why would I try one with less or same capacitance it makes no sense logically.

author: 2N3055
author_rank: Super Contributor
timestamp: May 02, 2024, 01:58:29 pm
content: Quote from: Michelle on May 02, 2024, 01:51:20 pmOk, that's a good info.Sure,with old scopes with physical switches, dirty contacts are very common.For cleaning use pure IPA (Isopropyl alcohol, not the beer!).Make sure to check in service manual (available on Internet) to see if any lubrication is prescribed or contacts.

author: Michelle
author_rank: Contributor
timestamp: May 02, 2024, 02:02:54 pm
content: Thanks, I will give it some cleaning then try one of my probes again, and if it's still not working at that point I now know I will need a higher capacitance probe. That's good to know this unit probably works. It would be a shame to see it go to waste, even if it's sort of obsolete it's still aesthetically pleasing and could be fun to use.Thanks for the suggestions. I wasn't sure if it was OK to just hook up a bare wire. I'm wary of messing up lab equipment!

author: tggzzz
author_rank: Super Contributor
timestamp: May 02, 2024, 02:16:26 pm
content: Quote from: Michelle on May 02, 2024, 01:43:35 pmAll standard *10 10Mohm probes should be re-compensated every time they are moved to any different scope. In theory the compensation ought to be checked when moved to a different input on the same scope, but I don't know anybody that bothers.

author: Michelle
author_rank: Contributor
timestamp: May 02, 2024, 02:44:32 pm
content: Quote from: tggzzz on May 02, 2024, 02:16:26 pmI compensate them every time but I didn't realize that I had to spell out the fact that I know how to do that and that it was the first thing I tried, and also the entire reason I hooked up the probe to the CAL signal to begin withAnyway thanks to people providing actually helpful information instead of repeating the absolute most basic stuff and assuming I know 0 at all.

author: tggzzz
author_rank: Super Contributor
timestamp: May 02, 2024, 02:56:49 pm
content: Quote from: Michelle on May 02, 2024, 02:44:32 pmThat could have easily been avoided if you had given the relevant information in your first post. Several people have pointed out that lack of information, and you have ignored all of them. Perhaps paragraph 3 ofhttps://entertaininghacks.wordpress.com/library-2/good-questions-pique-our-interest-and-dont-waste-our-time-2/might help in the future.Anyway, won't spend any more of my time helping you in the future.

author: Michelle
author_rank: Contributor
timestamp: May 02, 2024, 03:23:13 pm
content: Quote from: tggzzz on May 02, 2024, 02:56:49 pmLiterally in the title of the thread it says it's the calibration square wave signal, if by help you just mean mansplain and assume I don't know anything then I don't need your help. If you read the things I posted you would see that I eventually provided all of the relevant information yet you still tried to mansplain to me how you're supposed to calibrate the probe every time.Other people though have given me useful troubleshooting info.And yes I'm being snarky because I always get treated this way and it gets tiring. I am a real engineer and probably know a lot more than you think. I need to just stay off of internet forums. Never argue with a guy with 19000+ posts

author: bdunham7
author_rank: Super Contributor
timestamp: May 02, 2024, 03:43:11 pm
content: Quote from: Michelle on May 02, 2024, 01:43:35 pmThe reason I assumed you don't have another oscilloscope handy is that if you do, the totally obvious thing to do is to look at the calibrator output of the Iwatsu with a known good scope and vice versa. You've verified that there is a problem with the oscilloscope but now you would want to determine whether it is the calibrator output or a problem with the rest of the oscilloscope. With the additional information you provided it seems clear that the problem is with the scopes input circuitry, but have you tried the other channel?As for others making assumptions about your gender and "mansplaining", the real issue is that despite other advanced knowledge you may have as an automation engineer, you are asking a very basic question here that reflects a lack of familiarity with the topic at hand. If the topic is old analog scopes, I'm pretty sure you could learn quite a lot from this forum and plenty of people will be happy to help. Other new members have asked similar questions and gotten similar answers so nobody is discriminating against you. I see nothing in your initial query that would indicate that you know about calibrating probes. In fact, your comment about the Agilent probes being "similar" because they have aninputcapacitance of 12pF indicates that your knowledge of the matter isn't as complete as you might imagine. But I won't "mansplain" what the term "compensation range" means to you unless you ask since it probably isn't relevant to your immediate issue.

author: tggzzz
author_rank: Super Contributor
timestamp: May 02, 2024, 05:05:42 pm
content: Quote from: Michelle on May 02, 2024, 03:23:13 pmI have many calibration square wave signal sources; most are not part of a scope.Yes, you dideventuallyprovide all of the relevant information. Given that youdidn'tpost it initially, and the very basic question, the reasonable initial presumption was that you are an inexperienced beginner. I'm not the only one to think that.Why do you think "19000+ posts" is relevant? I don't. Rather than "stay off of internet forums", I suggest it would be better to use themeffectivelyas a communication mechanism.

author: Michelle
author_rank: Contributor
timestamp: May 02, 2024, 06:40:09 pm
content: You’re right, next time I should fully explain what I’ve done, am trying to do, and all relevant information. For now I’m going to clean the contacts because I didn’t realize that might have been an issue specifically the v/div knob affecting the waveform display... I did try ch2 with the same result and I do understand the capacitance adjustment range and ordered a $20 probe master from eBay that should work.Thanks for the help. I think cleaning and the new probe will get it back in order.

author: tggzzz
author_rank: Super Contributor
timestamp: May 02, 2024, 06:51:05 pm
content: Quote from: Michelle on May 02, 2024, 06:40:09 pmYou're welcome.Cleaning often worksunexpectedwonders, but with some 60s/70s/80s Tek scopes you have to be careful of the mechanical switch construction and only use IPA to clean.The other traditional problems are dried-out electrolytics, and the (most "entertaining") RIFA capacitors.

author: bdunham7
author_rank: Super Contributor
timestamp: May 02, 2024, 07:18:30 pm
content: Quote from: Michelle on May 02, 2024, 06:40:09 pmThat's interesting. The input circuitry, including the circuitry and attenuator switches actuated by those V/Div knobs, are not shared between channels. Seeing the problem on both channels more or less rules out a lot of things.

author: edpalmer42
author_rank: Super Contributor
timestamp: May 02, 2024, 07:55:24 pm
content: Quote from: bdunham7 on May 02, 2024, 07:18:30 pmNot necessarily. Both switches have been in the same environment. If they've been sitting around unused for years, it wouldn't surprise me to find that both of them are similarly oxidized. Actually, just spinning the switches back and forth a few times might be all that's required to cut through the oxide layer.Michelle, another reason to always start with the basics is that lots of beginners read these messages. When I answer a question I often 'play to the audience' rather than just the OP. Besides, although I'm an electrical engineer, I don't know shit about automation engineering so if you ever answer a question from me I hope you'll use words of one syllable or less! We're all beginners!Ed

author: Michelle
author_rank: Contributor
timestamp: May 02, 2024, 08:15:33 pm
content: Quote from: bdunham7 on May 02, 2024, 07:18:30 pmYeah I’m not totally sure what to make of it, based on the fact that I got a square wave from the bare wire on ch1 after turning the knob I figured the most logical next step would be to get an appropriate probe then see what happens on both of the channels. I didn’t try the bare wire on ch2 though, I just tried tuning the lecroy probe on it like I did on ch1. But now that the bare wire somehow went from the swept signal to the square wave I’m going to try both my lecroy and Agilent probe tomorrow just to see what happens.Another theory I had was that it could have something to do with it having warmed up for longer, even though the other day I left it on for a couple hours before even trying the probe, and it was only on for about a half hour today before I tried the bare wire.It could be that it was just chance that turning the knob wore through oxidation.

author: Michelle
author_rank: Contributor
timestamp: May 02, 2024, 08:20:29 pm
content: Quote from: edpalmer42 on May 02, 2024, 07:55:24 pmYou’re right it probably makes just as much sense to assume someone didn’t do something basic as it does to assume they did. Either way I realize I need to provide more information at least on a forum like this where people can actually understand what you’re saying.Sorry for having an attitude earlier I needed to eat lunch lol.