old oscilloscope - Page 1
Forum section: electronics / beginners

author: glinjik
author_rank: Regular Contributor
timestamp: February 25, 2023, 03:20:27 pm
content: hi i got given an old soviet oscilloscope c1-83 it seems to be working but as soon as i connect a probe i get a sinewave any ideas?

author: CountChocula
author_rank: Unknown
timestamp: February 25, 2023, 03:46:18 pm
content: What frequency? Are you perhaps picking up the mains frequency somewhere?

author: glinjik
author_rank: Regular Contributor
timestamp: February 25, 2023, 04:03:14 pm
content: ive got it set at 50 ms 10 mv dc and ac same thing

author: Zenith
author_rank: Frequent Contributor
timestamp: February 25, 2023, 04:13:26 pm
content: My guess is also that it's picking up mains frequency. Are you using a proper probe or a bit of wire?Almost all scopes have a calibrator output that provides a square wave of maybe 1V peak to peak at around 1 KHz. It looks as if it may have one towards the bottom right of the panel. Try that and you should see a square wave. It might take some fiddling with the timebase etc.What happens when you set the output to GND?If it's faulty, it looks as if the service manual is available from Electrotanya etc.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: February 25, 2023, 04:26:23 pm
content: Scope impedance is quite high, and it's normal that if you touch the probe with a finger you get some 70Vac. Your body is an antenna that picks up the mains hum from the circuits in the wall, and your finger transfers it to the scope input.

author: glinjik
author_rank: Regular Contributor
timestamp: February 25, 2023, 04:35:04 pm
content: if i set it to ground get normal flat signal, using proper probes, cant see any output for square wave

author: glinjik
author_rank: Regular Contributor
timestamp: February 25, 2023, 04:43:06 pm
content: found the manual but its in Russian and a photographic copy so unable to translate

author: Doctorandus_P
author_rank: Super Contributor
timestamp: February 25, 2023, 05:00:17 pm
content: Quote from: glinjik on February 25, 2023, 04:43:06 pmApplications that can do OCR from video and do real time translation have been around for quite some years now.

author: glinjik
author_rank: Regular Contributor
timestamp: February 25, 2023, 05:01:45 pm
content: thank you never thought of that

author: Zenith
author_rank: Frequent Contributor
timestamp: February 25, 2023, 05:13:22 pm
content: The calibrator output is usually a metal eye or short bar you can hook the probe onto conveniently. It's normally used to adjust the probe for correct response. In this case it would be useful to check whether the scope is showing any sign of working properly.It might be under the bottom right of the screen. The picture isn't clear and I don't know Russian.To get anywhere with this you need to find a way to provide the scope with a known signal it's likely to be able to cope with easily. Say in the audio range and anything from 0.5V to 5V peak to peak. If you don't have an audio signal generator, maybe you could tinker one together with a 555 timer, or get one of the £6 function generators from ebay.

author: shapirus
author_rank: Super Contributor
timestamp: February 25, 2023, 05:23:09 pm
content: Need a better picture. There doesn't seem to be a square generator output, but the picture isn't good enough to tell.p.s. I assume you did try to short the probe tip with its ground clamp which should produce a flat line on the screen. Of course when the signal input is floating it is going to pick up interference which will look like a sine wave on the screen.

author: glinjik
author_rank: Regular Contributor
timestamp: February 25, 2023, 05:52:50 pm
content: these settings on each channel give a square wave signal there is no place to hook up the probe ?

author: BillyO
author_rank: Super Contributor
timestamp: February 25, 2023, 06:10:33 pm
content: Can you post a larger picture?

author: glinjik
author_rank: Regular Contributor
timestamp: February 25, 2023, 06:25:11 pm
content: trying to get a good picture is difficult

author: Gyro
author_rank: Super Contributor
timestamp: February 25, 2023, 06:58:12 pm
content: Yes, that sort of distorted sinewave is typical of mains field pickup from the environment.

author: BillyO
author_rank: Super Contributor
timestamp: February 25, 2023, 07:03:54 pm
content: It does not look like it has a probe compensation output.Do you have any other signal you can connect it to? I does look like mains pickup. but the frequency does not look quite right. The period should be 20ms not 4ms. 4ms is 250Hz.

author: glinjik
author_rank: Regular Contributor
timestamp: February 25, 2023, 07:18:27 pm
content: i have an isolated power supply so gonna hook it up tomorrow and see what difference it makes

author: james_s
author_rank: Super Contributor
timestamp: February 25, 2023, 07:26:08 pm
content: An isolated power supply is not what you need here, you need something that will produce a signal. It looks to me like the scope is working properly, the problem is you don't know how to set it up and use it. Find a source of a known test signal, build a multivibrator with a couple of transistors or a 555.

author: shapirus
author_rank: Super Contributor
timestamp: February 25, 2023, 07:50:43 pm
content: Quote from: BillyO on February 25, 2023, 07:03:54 pmyeah exactly, the 250 Hz wave doesn't look right.need a known signal source to debug this.also, how exactly is the probe set up? how is it connected? can we see a picture?p.s. yes there is no 1 kHz signal output as far as I can see.

author: themadhippy
author_rank: Super Contributor
timestamp: February 25, 2023, 09:00:50 pm
content: Quoteisolated is most defiantly what you want,a simple drop down transformer would be suitable

author: Bud
author_rank: Super Contributor
timestamp: February 25, 2023, 09:07:58 pm
content: You should set the Fine Tune ms control fully clockwise, the displayed stray signal period then should match your local mains voltage period.This scope has calibrator output on the left rear side, that was easy to find by checking googled photos.

author: james_s
author_rank: Super Contributor
timestamp: February 26, 2023, 12:36:48 am
content: Quote from: themadhippy on February 25, 2023, 09:00:50 pmFor what? It sounded like he wanted to provide isolated power to the scope to float it in attempt to reduce the noise. If he wants to measure the output of a transformer then yes an isolated transformer with a low voltage secondary will work well.

author: BillyO
author_rank: Super Contributor
timestamp: February 26, 2023, 04:35:16 am
content: Quote from: themadhippy on February 25, 2023, 09:00:50 pmNot sure what you mean by this but most mains voltage conversion transformers are autotransformers. Those are not isolated. If you are talking about a 240V to 12V power supply transformer, then okay, but it seems to me there are possibly better ways to get a known signal source.

author: glinjik
author_rank: Regular Contributor
timestamp: February 26, 2023, 02:19:32 pm
content: it puts out 1k signal in square or a flat line but is just for calibrating the screen

author: Gyro
author_rank: Super Contributor
timestamp: February 26, 2023, 02:26:51 pm
content: Not for calibrating the screen, but for adjusting the scope probes to have proper response on their x10 setting (if they are x1/10 switchable that is). You connect the probe to the cal output and adjust the little trimmer on the probe to give a square flat topped signal with no undershoot or overshoot.Have you tried the fine tune timebase knob yet? It is very strange to pick up a 250Hz signal from the environment, you need to make sure the little timebase centre knob if in its cal position (normally fully colockwise).

author: glinjik
author_rank: Regular Contributor
timestamp: February 26, 2023, 02:42:55 pm
content: tryed everthing lol i think the problem is modern probes simply will not work found this picture of original probes dont appear to have compensation i did tyy that output does nothing at all

author: shapirus
author_rank: Super Contributor
timestamp: February 26, 2023, 02:52:17 pm
content: Modern probes work with these scopes just as well as their native ones do.

author: glinjik
author_rank: Regular Contributor
timestamp: February 26, 2023, 02:55:17 pm
content: its beyond me i think the parts bucket is looking good

author: Zenith
author_rank: Frequent Contributor
timestamp: February 26, 2023, 03:38:37 pm
content: It doesn't seem to be a high specification sought after instrument, but it seems a shame to break it up or throw it away without giving it a proper try.I have the impression you don't have much experience with oscilloscopes.

author: wasedadoc
author_rank: Super Contributor
timestamp: February 26, 2023, 03:47:44 pm
content: Quote from: glinjik on February 26, 2023, 02:42:55 pmThat black "stick" in the right hand half of the box looks like a tool for adjusting a probe compensation screw.

author: glinjik
author_rank: Regular Contributor
timestamp: February 26, 2023, 03:52:06 pm
content: i had a look on YouTube lots and lots of videos on old soviet oscilloscope and they are all using original probes before i throw it i will try and get hold of some probes

author: Zenith
author_rank: Frequent Contributor
timestamp: February 26, 2023, 04:52:04 pm
content: I suspect this thing basically works, or you wouldn't have got it to display the rough sine wave that looks like mains pick up. It may not work very well, but it works.You may have a faulty probe. Someone said the calibration signal was brought out at the back. It's not unknown for calibrators not to work.I can't imagine the Russian probes this came with, would make the difference between being able to display something or nothing. At worst you may not be ableto compensate other probes properly.If you bought the Russian probes, you'd still have the problem of providing a suitable test signal of a few hundred Hz to a few KHz, at a sensible voltage.I suggest you concentrate on making or buying a signal generator - something crude would do. It doesn't have to be the last word in signal generators. If you had such a thing, say based on a 555 timer, you should be able to get the scope to display something you'd expect, even if you connected it to the inputs with a couple of short pieces of wire,

author: shapirus
author_rank: Super Contributor
timestamp: February 26, 2023, 05:04:04 pm
content: Quote from: Zenith on February 26, 2023, 04:52:04 pmThat's an old-school looking probe built to survive a nuclear bombing. Not different in terms of compatibility from any probe, it will work on any scope, as well as any regular probe will work on this scope.p.s. I own a similar scope, a simpler one, a single-channel С1-75. It's a normal oscilloscope like any other. It doesn't require any knowledge beyond what is required to operate any other scope. It shouldn't even require to understand Russian to use it, since all the controls are pretty much obvious.p.p.s. Don't throw it out. It looks like a good working scope. We have yet to see any evidence of it being broken, so far we hardly saw any.

author: james_s
author_rank: Super Contributor
timestamp: February 26, 2023, 05:24:07 pm
content: Why are you avoiding building some kind of test circuit? Surely if you have any use for an oscilloscope you've got a few parts laying around? 555 ICs are cheap and ubiquitous, and the classic multivibrator requires only a pair of transistors, capacitors and resistors. A modern probe should work just fine with that scope, I see nothing to suggest that compensation is an issue, that's set using a square wave.

author: f4eru
author_rank: Super Contributor
timestamp: February 26, 2023, 06:29:40 pm
content: Quote from: Zenith on February 26, 2023, 04:52:04 pmInterrupted ground on the BNC would yield a higher 50 Hz pickup

author: Gyro
author_rank: Super Contributor
timestamp: February 26, 2023, 06:41:35 pm
content: That does look like a decent probe set, it even has proper adaptors to match the probe tips into a BNC socket. The compensating trimmer is most likely on the end that plugs into the scope.If you scope display goes flat when you hold the probe's grounding clip against its bare tip then it is working ok.

author: shapirus
author_rank: Super Contributor
timestamp: February 26, 2023, 07:00:07 pm
content: Quote from: Gyro on February 26, 2023, 06:41:35 pmI suggested this earlier in this thread, but never heard back whether it was tried and what was the result.

author: glinjik
author_rank: Regular Contributor
timestamp: February 26, 2023, 07:38:56 pm
content: so after watching a video on you tube and messing around made a square wave generator from LM324N and the result is below what i did find is it had an adapter double bnc type i pulled it off and connected straight to the original bnc and sine wave disappeared what i found though is if you touch just about anything the signal jumps about, think its just old, contacts maybe dry have to take a peak insidei realise that lm chip is not great but dont have a 555 at hand

author: shapirus
author_rank: Super Contributor
timestamp: February 26, 2023, 07:57:49 pm
content: Can you show us your circuit schematics and how you connect the probe?p.s. LM324 is an awesome chip.

author: glinjik
author_rank: Regular Contributor
timestamp: February 26, 2023, 08:12:14 pm
content: ground clip to ground probe to pin1 running on a 9v battery pot set at 50k oscilloscope 50 mv / 0.5ms

author: shapirus
author_rank: Super Contributor
timestamp: February 26, 2023, 08:19:27 pm
content: btw this scope does have a 1 kHz probe calibration output. the manual says it's on the left side panel of the device and marked as on the attached image. the question is whether it works, though.

author: glinjik
author_rank: Regular Contributor
timestamp: February 26, 2023, 08:27:36 pm
content: hi yes found that out earlier when in calibration mode you can switch it square wave or flat line but the output does nothing tried today

author: shapirus
author_rank: Super Contributor
timestamp: February 26, 2023, 08:36:12 pm
content: Quote from: glinjik on February 26, 2023, 08:12:14 pmThis circuit does not work in simulation with a single supply, which you have with the 9V battery. It needs dual supply to work, or the virtual ground has to be created. Try the attached variant. Simulation shows that it will oscillate at about 12 Hz. Waveform is terrible and duty cycle is unstable (not sure what it will be in real life), but at least it'll work.Probe ground clip to either battery minus or the divider middle point, probe tip to IC pin 1.(just to make sure, battery positive goes to pin 4, battery negative to pin 11)

author: glinjik
author_rank: Regular Contributor
timestamp: February 26, 2023, 08:52:15 pm
content: just done a quick sim looks great i will have a go at it tomorrow thank you

author: james_s
author_rank: Super Contributor
timestamp: February 28, 2023, 04:03:10 am
content: Try this, it's one of the very first circuits I remember making when I was a kid. You might want smaller capacitors than the 1uF they show here though.https://rayshobby.net/wordpress/learning-electronics-1-multivibrator/Or here are some oscillators you can build with a CMOS inverter.https://www.ti.com/lit/an/szza043/szza043.pdfThe Colpitts oscillator is another simple one.https://www.homemade-circuits.com/lc-oscillator-circuit-how-it-works/You could also look for some of those TTL oscillator cans, those just need 3.3 or 5V and output a (usually) square wave at the frequency printed on them.

author: EPAIII
author_rank: Super Contributor
timestamp: February 28, 2023, 07:00:50 am
content: TEST NUMBER ONE:Ground the tip of your probe. You can easily do this by touching it to the outer part of one of the BNC probe jacks. You should get a flat line on the display. If you don't, then something is wrong.If you want to eliminate the probe as a possibly defective part, a very simple, almost fool proof probe can be a length of coaxial cable with a BNC connector on one end. Strip it to expose the inner conductor and use that bare conductor as your probe tip for the above test. This would be an uncompensated, 1X probe. Actually a length of ordinary hook-up wire to the center pin of a BNC connector would do the same thing.If you do get a flat line that way, then, AND ONLY THEN, start with some kind of signal generator or the built in, 1KHz calibrator.

author: glinjik
author_rank: Regular Contributor
timestamp: March 07, 2023, 02:04:58 pm
content: after messing about and doing as suggested i got hold of a 555 timer and made up the circuit below then some more messing finally a result as below, its a finicky old scope one touch of any control and it starts misbehaving, i clamped a ferrite core onto the power cord and well results below thanks to all your replies and help and not once did someone say get back to basicsps the square wave is a little difficult to see

author: rstofer
author_rank: Super Contributor
timestamp: March 07, 2023, 03:06:25 pm
content: Got an Arduino laying around? The tone() function will provide a nice square wave.

author: glinjik
author_rank: Regular Contributor
timestamp: March 07, 2023, 03:24:49 pm
content: no not got arduino, but im satisfied it works although temperamental i think a poke about inside check caps and some switch cleaner will do a world of good

author: Zenith
author_rank: Frequent Contributor
timestamp: March 07, 2023, 11:39:22 pm
content: You got this thing as a gift, it's a working scope, you put together the 555 oscillator to check it out. Everything a win so far.You have started on a fascinating voyage of discovery.