EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: DennisCA on September 29, 2021, 12:40:22 pm
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Hello, I am looking at possibly buying a scope.
I think it could be useful when working on repairing old equipment and perhaps help me deepen my knowledge of electronics (just from finding new stuff to play with I guess).
I am currently working on things such as cassette decks and amplifiers (for my own use) and I have worked on welders. Mostly older stuff. I admist I have not yet needed a scope to fix them. I understand a scope can be good for audio purposes though, particularly for tuning a cassette player it'd be useful.
I was looking at local 2nd hand ads and found a Hameg 404 for 100€, it's a 40mhz analog scope, would this be a good beginners scope? Is the price decent?
(https://i.imgur.com/JaibWTK.jpg)
I was also recommended to look at some of the new handheld digital scopes, such as the Mini DSO203 which is in a similar price range, but digital. Though I have read some negative stuff on this on these forums when I googled it.
Hameg seems to be german quality engineering, though it's less capable in terms of features as well as bulky (tho I have the space) and it might be of that age where it needs servicing, but seller claims it's fully functional.
I guess on an emotional l level I like the old analog CRTs (I like old tech in generaö), but I try not to let it affect my decision making.
To be honest I am open to the idea that I don't need a scope yet, maybe I should get an electronics book instead. All feedback is apprecaited though, I know a lot of beginners wanna get the next tool before they have a need for it and I might suffer from that too.
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Lots of opinions coming. I'd prefer the price a little lower but I say yea sure, it's fine to start out with for what you are going to work on.
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For analog id go with the tek 22xx series you may source something for 50bucks, simple, easy to source and repairable. Id definitely get a used digital (lots of rigols/agilents with pretty decent uses but low on memory, which does not seems to be a need for you).
Id totally avoid teks tdsxxx series as they are terrible to use (slow as fuck)
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I was looking at local 2nd hand ads and found a Hameg 404 for 100€, it's a 40mhz analog scope, would this be a good beginners scope? Is the price decent?
No, not for 100 but for max 30 to barely 50 it could, depending on condition. since you mention your circumstances you could as well just add 20euro and go for a all in one thing.
https://usa.banggood.com/OWON-HDS200-Series-2CH-Handheld-Oscilloscope-40-or-70MHz-Bandwidth-20000-Counts-Multiumeter-OSC-+-DMM-+-Waveform-Generator-3-in-1-Suitable-for-Automobile-Maintenance-and-Power-Detection-p-1802427.html?cur_warehouse=CN&ID=6301777&rmmds=search (https://usa.banggood.com/OWON-HDS200-Series-2CH-Handheld-Oscilloscope-40-or-70MHz-Bandwidth-20000-Counts-Multiumeter-OSC-+-DMM-+-Waveform-Generator-3-in-1-Suitable-for-Automobile-Maintenance-and-Power-Detection-p-1802427.html?cur_warehouse=CN&ID=6301777&rmmds=search)
https://www.youtube.com/watch?v=Y5tBPK34RSU (https://www.youtube.com/watch?v=Y5tBPK34RSU)
https://www.youtube.com/watch?v=fiZrZFvIkww (https://www.youtube.com/watch?v=fiZrZFvIkww)
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If you don't mind paying a bit more for a HDS200 you can get rebadged versions from
farnell and element14 (multicomp MP720780, MP720782, MP720781, MP720783).
There's also an EEVblog thread:
https://www.eevblog.com/forum/testgear/owon-hds-200-handheld-oscilloscope-w-builtin-dmmawg/ (https://www.eevblog.com/forum/testgear/owon-hds-200-handheld-oscilloscope-w-builtin-dmmawg/)
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Judging by the logo on the screen I would guess it is one of the later analog scopes produced. The most usually seen fault would likely be failing caps in the power supply, so the newer the better. Can you get a copy of the factory service manual? One of the advantages of the old Tek scopes is that they have excellent service manuals and most of them are available free or cheap.
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I found the regular manual, the front of the scope says 404, but the bottom plate says it's a 404-2:
https://www.sm5cbw.se/hameg/hmosc/hm404-2.pdf (https://www.sm5cbw.se/hameg/hmosc/hm404-2.pdf)
(https://i.imgur.com/wDYqPag.png)
And the service manual here
https://elektrotanya.com/hameg_hm404-2_oscilloscope_sch.pdf/download.html#dl (https://elektrotanya.com/hameg_hm404-2_oscilloscope_sch.pdf/download.html#dl)
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If you would like to learn how to use a scope properly with analogue circuits, you should definitely start with an analogue scope. The important bit is that analogue scopes do not lie. What you see is what you get. This Hameg looks good and the price is fair for its age and condition. I still use a very similar Hameg at work for fault-finding and HV work when a 10K Tek DSO feels somewhat less expendable. At home I deal with analogue circuits almost exclusively and use a couple of old analogue Teks. I do have a DSO but it gets switched on perhaps twice in a year.
Cheers
Alex
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My personal opinion: If you're interested to learn about analog electronics I'd grab that scope if it's working and comes with probes. I don't think 100EUR is so bad for Europe. Hameg scopes are simple and usually reliable. For checking out or alining Tape decks or amps it's ideal.
You're saying you're new to scopes. I firmly believe it's easier to get to know how a scope works and how to drive it using an analog scope.
A digital scope has so many functions it could be overwhelming for a beginner.
I admit I do not know most digital handheld scopes, but what I've seen so far was mostly dreadful. Most cheap handhelds have a terrible UI and are often buggy. If you want a digital scope go for one of the entry level proper scopes that are around. Or maybe even an older HP/Agilent 516xx scope. I find those are miles ahead of e.g. a Rigol DS1054z. I've recently bought a 54621A and it has replaced the Rigol on my bench for the most part. The UI is responsive, logical and simple. It's a joy to use.
Or maybe I'm just used to analog scopes and love the green glow and the clicky knobs? YMMV. You can always flog the Hameg if you find it's not for you.
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I found the regular manual, the front of the scope says 404, but the bottom plate says it's a 404-2:
https://www.sm5cbw.se/hameg/hmosc/hm404-2.pdf (https://www.sm5cbw.se/hameg/hmosc/hm404-2.pdf)
(https://i.imgur.com/wDYqPag.png)
And the service manual here
https://elektrotanya.com/hameg_hm404-2_oscilloscope_sch.pdf/download.html#dl (https://elektrotanya.com/hameg_hm404-2_oscilloscope_sch.pdf/download.html#dl)
Interesting that the x-ray dose is specified in "pA/kg", the SI version of the older Röntgens/sec, the measure of ionization in air, rather than in Gy/hr or Sv/hr, the SI units of dose rate (energy deposition).
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I'd get the Hameg. If that is the article in question, looks like it is in nice shape. It will serve you well. Handheld scopes honestly kinda suck to use unless you really need one (and you don't for the stuff you mentioned)...you'll enjoy the controls of the Hameg much more.
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If it is in good condition (and it looks so) and the 100€ isn't a frightful amount of money for you, go for it. You might have been able to buy them cheaper a few years ago, but stuff like this seems to be going for a lot of money nowadays, even in junk condition. Paying a few extra bucks for a nice one is a much better idea.
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At least in the pictures that Hameg looks pretty nice, 100EUR sounds high to me but I know prices for used test gear in other parts of the world tend to be higher than here and the selection is more limited. I normally recommend digital, but the digital scopes you can buy new in that price range are pretty much toys, for the sort of work you want to do a good analog scope is probably a better choice at that price point. If you could afford more I'd recommend one of the Rigol or Siglent DSOs but they are going to be around 3x the price. You might see if you can talk them down a bit on price, an offer of 80EUR is probably a reasonable starting point.
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Thanks for all the feedback, I put in an offer on the Hameg. I am a bit skeptical of these small handheld scopes.
Maybe some day I'll invest in a proper DSO or find a good deal on a used one, but this will hopefully be mine and serve me until that time. I note that this scope seems ot have a recall and save button, so I think it might have some digital features.
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In your position I would choose the Hameg too.
Look at the CT button on the lower left corner, it is a curve tracer function that some Hameg scopes have, very nice and not common to see.
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Handheld scopes honestly kinda suck to use unless you really need one (and you don't for the stuff you mentioned)...you'll enjoy the controls of the Hameg much more.
I would have said the same thing. The "handheld" scopes in that price range are toys compared to a older analog oscilloscope with real 1 megohm BNC inputs.
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Hello, I am looking at possibly buying a scope.
I think it could be useful when working on repairing old equipment and perhaps help me deepen my knowledge of electronics (just from finding new stuff to play with I guess).
I am currently working on things such as cassette decks and amplifiers (for my own use) and I have worked on welders. Mostly older stuff. I admist I have not yet needed a scope to fix them. I understand a scope can be good for audio purposes though, particularly for tuning a cassette player it'd be useful.
I was looking at local 2nd hand ads and found a Hameg 404 for 100€, it's a 40mhz analog scope, would this be a good beginners scope? Is the price decent?
(https://i.imgur.com/JaibWTK.jpg)
I was also recommended to look at some of the new handheld digital scopes, such as the Mini DSO203 which is in a similar price range, but digital. Though I have read some negative stuff on this on these forums when I googled it.
Hameg seems to be german quality engineering, though it's less capable in terms of features as well as bulky (tho I have the space) and it might be of that age where it needs servicing, but seller claims it's fully functional.
I guess on an emotional l level I like the old analog CRTs (I like old tech in generaö), but I try not to let it affect my decision making.
To be honest I am open to the idea that I don't need a scope yet, maybe I should get an electronics book instead. All feedback is apprecaited though, I know a lot of beginners wanna get the next tool before they have a need for it and I might suffer from that too.
Between these two. With your description about you and your use and needs etc...
I do not think even one second between this utterly useless toy Mini DSO203 an this displayed Hameg here.
Specially if you know this Hameg is in good condition, as it looks like in this image really nice condition with display (if some test signal displayed also... then know more. ) best if you buy it in Finland locally and can check (or very trusted seller).
If/when your needs rise later, you also know more what things you need from scope your next move is buy modern real digital oscilloscope. (What recommend to do now but not The Toy, but yes, it need more money and still, these bit better analog scopes are somehow nice, specially with repair/service older things. )
With this Hameg you can in real time look everything what you have told about your needs. With this SainSmart DSO203 toy, you come only frustrated, angry and get lesson how to loose money, they are just made for fooling money from peoples who do not know enough and do not have any experience.
( Fi: Kai olet ostamassa sitä suomalaiselta tai muuten paikallisesti suoraan jotta voit varmistua kunnosta ja ehkä yrittää tinkiäkin hinnasta! Hamegit kuuluu oikeasti ns hyvän laadun luokkaan. Jos kunto on lähes "mint" ja mukana hyvät probet, hinta lienee lähellä oikeaa. Aikalailla suorastaan monipuolinen skooppi kun katseli user manuaalia.)
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I was able to bargain it down a little, enough that it covered the shipping costs (Matkahuolto). Scope was in Oulu and I am near the Vaasa area, south of it. So it was not possible for me to test it in, but it was sold as fully functional and pictures looks like it's been well taken care of.
If am real lucky it'll be here tonight, but more likely on monday.
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It did arrive today, fast shipping!
It looks to be in fine order. I watched eevblogs video on how not to blow your scope up and now i am very afraid to hook it up to anything lol - But I hooked it up to my cassette decks output (deck power plug has no earth pin), so i had something to take a photo of. As far as I can tell everything looks to be in order.
(https://i.imgur.com/3MtqB34h.jpg)
(https://i.imgur.com/LQsa85eh.jpg)
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You shouldn't be afraid to hook it up to anything, just stay away from the mains side of anything. If the device you are testing has a switchmode power supply just stay out of the power supply entirely. If it has an iron transformer, stay on the secondary side. As long as you do that everything will be fine.
Looks like a real nice scope, I think it will serve you well. Pick up a set of P6100 probes if you don't have probes with it already, they're quite good despite their low cost.
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IT all looks very clean and nice. Hameg is a good brand and the on-screen measurements are a cut above the average CRT 'scope.
If it all works then I'd say it's definitely worth 100 Euros. :-+
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Thanks for posting photos of your new scope, it seems to be in mint condition, congratulations!
These cursors/on screen measurements are very handy.
If you have a diode around, try to use the scope curve tracer, pressing the CT button - "Component Tester". You should see a nice I-V curve.
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Just remember to use the 10X probes to protect the scope and get better measurements.
It is a lot harder to damage the input of a scope using a 10X probe.
When uncertain use AC coupling, DC coupling is for measuring DC volts and it will do this nicely, it is cool to see the line go up and down with change in DC volts but usually this is only used for small voltages, Like tuning volts on a PLL.... like 0-10 volts although it will measure lots more. best to use a voltmeter for higher volts.
The high input impedance of scopes makes it better in some aspects for measuring small DC than some volt ohm meters.
Try measuring DC volts on a small battery for example, to see how it works and how accurate it is.
These older low freq scopes are easier to use on audio frequencies than the computerized digital scopes. In my opinion, also much better. Just my opinion.
About the price, seems quit good even for USA. You will learn a lot. Think of how much an electronics course would cost.
For accurate traces use a probe that is matched to your input. I think your input is 20 Pico Farad. These low freq probes are cheap. If you dont have the correct probe, you will get unreliable traces.
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It did arrive today, fast shipping!
It looks to be in fine order. I watched eevblogs video on how not to blow your scope up and now i am very afraid to hook it up to anything lol - But I hooked it up to my cassette decks output (deck power plug has no earth pin), so i had something to take a photo of. As far as I can tell everything looks to be in order.
(https://i.imgur.com/3MtqB34h.jpg)
(https://i.imgur.com/LQsa85eh.jpg)
It looks really good.
As shown in the attached manual, it also has a component testing function and also an RS232 remote control.
Forum member @w2aew has also made very good general instructional videos on the use of (analog) oscilloscopes. He really knows what he's doing. In addition, they are produced well and carefully and thoughtfully and calmly for easy follow and learn. Definitely in the real top class. There is enough authentic knowledge and experience and the teaching skills are good.
You can start here if you haven't already ...
https://www.eevblog.com/forum/beginners/oscilloscope-training-class-(long)/msg50100/#msg50100 (https://www.eevblog.com/forum/beginners/oscilloscope-training-class-(long)/msg50100/#msg50100)
Attached User manual
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Thanks, I'll check that out, as for the probes, I got two, one is a 1x-10x of this brand
https://www.globalmediapro.com/dp/A26S45/Pintek-CP-360-Scope-Probe-60MHz-pack-10-pcs/ (https://www.globalmediapro.com/dp/A26S45/Pintek-CP-360-Scope-Probe-60MHz-pack-10-pcs/)
The other probe says Pomona minipincer and does not have a resistor at all that I can see.
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FWIW, the original Hameg probes are rebadged Testec, a nice and affordable German prone brand. I like them a lot.
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FWIW, the original Hameg probes are rebadged Testec, a nice and affordable German prone brand. I like them a lot.
Me too. 1+ :-+
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For what you do take a cheap old one that works good.
No need for those digital scopes.
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Thanks, I'll check that out, as for the probes, I got two, one is a 1x-10x of this brand
https://www.globalmediapro.com/dp/A26S45/Pintek-CP-360-Scope-Probe-60MHz-pack-10-pcs/ (https://www.globalmediapro.com/dp/A26S45/Pintek-CP-360-Scope-Probe-60MHz-pack-10-pcs/)
The other probe says Pomona minipincer and does not have a resistor at all that I can see.
No specific brand recommendations, but I'd recommend getting yourself a pair of fixed 10X probes instead. Those switchable ones are ripe for a mistake down the road that might blow something up.
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The Hameg you purchased is perfect for audio repairs. If later on you venture into other aspects of electronics requiring more bandwidth, you can always upgrade to something more. In audio repairs there is little danger of blowing your scope.
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The Hameg you purchased is perfect for audio repairs. In audio repairs there is little danger of blowing your scope.
It's the "welders" that worry me...
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I've repaired old welders yes, usually it has just been a matter of replacing capacitors with new ones. Another thing that can wrong with them might be diodes or thyristors, in the types of welders I have anyway. No modern inverters. I don't really know if an oscilloscope would be of use there or not, but certainly it's a high power application. Fortunately my welders all work fine now... I have been thinking of building a pulse unit for my tig though, that's strictly a 10v affair however.
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The advice of only using fixed 10x probes is good advice. It can save your 'scope when the voltages get real.
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No specific brand recommendations, but I'd recommend getting yourself a pair of fixed 10X probes instead. Those switchable ones are ripe for a mistake down the road that might blow something up.
I don't like the switchable aspect either, but the P6100 probes are common and dirt cheap and they're quite reasonably made. I have a set of them on on of my older scopes that I just glued the switches in the 10X position so I wouldn't have to worry about it. I have never once that I recall intentionally used a scope probe in 1X mode.
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Great idea about the glue, I was having issues finding fixed 10x probes. Mostly 1/10x ones.
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Great idea about the glue, I was having issues finding fixed 10x probes. Mostly 1/10x ones.
You’re in Europe so you should have no trouble getting Testec probes at a reasonable price. They have fixed 10x probes.
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I was fiddling around the scope today, mostly just reading audiosignals from a player. I notice that the channel 1 input was not able to get the same kind of oscillation regardless of settings, it's as it'd diminished compared to the channel two input, I was able to get a much clearer audio signal through the 2nd channel. Is this an indication of something wrong, Iwould have thought both inputs should be able to show the same values when adjusted the same way.
Channel two
(https://i.imgur.com/CJaXQ9Rl.jpg)
Channel one
(https://i.imgur.com/5MXOuxQl.jpg)
edit: I think the probe might also be the cause (I can change the intensity by fiddlign with the wire), need to get new ones I can trust. Probe is in 10x mode all the time.
edit2: Nah I think it's the actual input port, now I am pretty sure there's a loose contact there.
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It doesn't look like you have one or the other input in "VAR" mode which would be uncalibrated and allow one channel to be adjusted in amplitude. I've run across older equipment that has dirty BNC female pins. Try to clean the inside of the BNC pin with a small cleaning tool like a small piece of hard paper or pipe cleaner and alcohol.
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... I just glued the switches ...
Or (transparent) heat shrink tube.
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It doesn't look like you have one or the other input in "VAR" mode which would be uncalibrated and allow one channel to be adjusted in amplitude. I've run across older equipment that has dirty BNC female pins. Try to clean the inside of the BNC pin with a small cleaning tool like a small piece of hard paper or pipe cleaner and alcohol.
None of them where in VAR mode that I could see, and now I am without a probe, the damn connector just came apart in my hands as I removed it. So I'll need two new ones at least.
Looking at testec, but someone said I earlier IS hould matchmy probes to my input, which is 1mΩ 20pf, can't find anything that matches that exactly though, so how important is it? A Testec TT-LF-312 is 10 MΩ, 15.5 pF for instance.
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It doesn't look like you have one or the other input in "VAR" mode which would be uncalibrated and allow one channel to be adjusted in amplitude. I've run across older equipment that has dirty BNC female pins. Try to clean the inside of the BNC pin with a small cleaning tool like a small piece of hard paper or pipe cleaner and alcohol.
None of them where in VAR mode that I could see, and now I am without a probe, the damn connector just came apart in my hands as I removed it. So I'll need two new ones at least.
Looking at testec, but someone said I earlier IS hould matchmy probes to my input, which is 1mΩ 20pf, can't find anything that matches that exactly though, so how important is it? A Testec TT-LF-312 is 10 MΩ, 15.5 pF for instance.
Passive probe have two capacitance specs: capacitance at tip, and capacitance compensation range on the side of the scope connector (in your case 1MOhm 20 pF). The capacitance you are looking for is compensation range one and yes, Testec probes are fine.. They have good range.
You don't need anything better than Testec TT-LF-312 (for 1X/10X probe)
https://www.reichelt.com/hr/en/modular-probe-15-150-mhz-x1-x10-testec-lf-312-p32416.html?&trstct=pos_0&nbc=1 (https://www.reichelt.com/hr/en/modular-probe-15-150-mhz-x1-x10-testec-lf-312-p32416.html?&trstct=pos_0&nbc=1)
https://www.reichelt.com/hr/en/double-set-of-15-150mhz-modular-probes-testec-lf-312-2-p32420.html?&trstct=pos_1&nbc=1 (https://www.reichelt.com/hr/en/double-set-of-15-150mhz-modular-probes-testec-lf-312-2-p32420.html?&trstct=pos_1&nbc=1)
OR
Testec TT-LF-212 (for 10X probe only)
https://www.reichelt.com/hr/en/modular-probe-150-mhz-x10-testec-lf-212-p32415.html?&trstct=pos_0&nbc=1 (https://www.reichelt.com/hr/en/modular-probe-150-mhz-x10-testec-lf-212-p32415.html?&trstct=pos_0&nbc=1)
Also maybe:
https://www.reichelt.com/hr/en/set-of-2-probe-tips-tastspitzen-p32435.html?&trstct=pos_0&nbc=1 (https://www.reichelt.com/hr/en/set-of-2-probe-tips-tastspitzen-p32435.html?&trstct=pos_0&nbc=1)
https://www.reichelt.com/hr/en/spring-hook-for-probes-federhaken-p7644.html?&trstct=pos_1&nbc=1 (https://www.reichelt.com/hr/en/spring-hook-for-probes-federhaken-p7644.html?&trstct=pos_1&nbc=1)
these get damaged and displaced so few spares are not bad to have.
P.S. also look at https://www.batterfly.com/shop/en?route=product/search&search=TESTEC (https://www.batterfly.com/shop/en?route=product/search&search=TESTEC) they have good choice and prices.
best,
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Try using the built in probe compensation calibrator, at least I assume it has one. Connect both probes to that and set both channels the same, you should see the same square wave on both. You could also get a cheap function generator and use that to play around, you'll probably want one of those anyway for working with audio circuits.
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I agree with the other comments about 1X 10X probes. I really do not like the 1X 10X probes,they can cause problems if you unintentionally have them set at 1X, Sometimes the switch can go wonky also. In general they do not work as well as unswitched probes, maybe stray capacitance?
I spent years with inadequate probes that did not match the scopes I was using. In retrospect, that was stupid. At the really cheap prices that are common today there is little reason not to get the correct probes. Usually good to get probes that are rated higher than your scope. since your scope is 40 MHz this should not be a problem. You do have a calibrator connector just under the screen for calibrating your new probes. Should be nice square wave.The BNC connector part of the probe should have an adjustment (really just an adjustable cap) that is used to make the wave square. This is what "matches" the capacitance of the probe with the input capacitance of the scope.
About max freq....in analog scopes this is usually the frequency where the trace is 80% of what is should be. The scope can go higher, sometimes much higher, but the amplitude of the trace will not be accurate. Sometimes there is a "hole" in the freq range just above the Max where the scope has low response then maybe the scope gets back on track with even higher freq.
That is a real nice scope. Much more than a "beginner" scope.
Don't clean the surface with any solvents, could erase the lettering, use soap if necessary
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Don't clean the surface with any solvents, could erase the lettering, use soap if necessary
I learned that the hard way with a Tek 2215 that was filthy. I washed the knobs in warm soapy water and they cleaned up beautifully, all the grime came right off, as did all of the printing on the transparent portion. |O
This scope doesn't appear to have anything like that though, just a screen printed vinyl overlay, those are pretty durable as long as you don't use any harsh solvents. I often use Windex or Oil Eater to clean off stubborn grunge but this one already looks clean.
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Don't clean the surface with any solvents, could erase the lettering, use soap if necessary
I learned that the hard way with a Tek 2215 that was filthy. I washed the knobs in warm soapy water and they cleaned up beautifully, all the grime came right off, as did all of the printing on the transparent portion. |O
This scope doesn't appear to have anything like that though, just a screen printed vinyl overlay, those are pretty durable as long as you don't use any harsh solvents. I often use Windex or Oil Eater to clean off stubborn grunge but this one already looks clean.
Ever had to deal with super duper permanent marker? I am in the middle of repairing a Tek Type 575 that someone wrote on (probably an auctioneer; fortunately on one of the side panels) with one of those ultra super duper permanent Sharpies. The only thing that would touch it was acetone. Took off some paint too, but not all of it, and it looks a damn sight better than the huge ugly handwriting. |O
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I've had reasonable luck removing permanent marker using that magic eraser melamine foam stuff. Sometimes it helps to moisten it with rubbing alcohol.
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Hello again, today my new probes arrived so I could test the scope. I used the 1khz signal generated by the scope itself. And it does seem there is something wrong with channel 1.
This is channel 2, I tuned both probes capacitance on channel two:
(https://i.imgur.com/pfe6K0Dh.jpg)
Channel 1, not able to get anywhere near even with 20mv on the volts/div knob
(https://i.imgur.com/KmjXpwqh.jpg)
On channel 1 I am not able to tune the capacitance to get flat square wave either. Signal seems both weaker and wrong. I am suspecting, well hoping that it's a bad connection to the BNC connector on front.
I suppose the next step is to open it up and have a look near the ch.1 connector....
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Ch 1 response looks exactly like a broken connection to the input circuitry, with only a small capacitance between the signal and the high-Z (1 megohm) input. If that BNC is a PCB-mount right-angle BNC, excess leverage against it in the past may have broken the solder joint between the "hot" pin and the PCB.
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I was going to say that looks like the input is very loosely AC coupled, but I see Tim said what is effectively exactly the same thing. It looks like the channel is mostly working just fine, but the path is broken somewhere near the input and capacitively coupling.
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Check the AC/DC switch contacts - that signal could be capacitatively coupled through a layer of dirt
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Started opening it up, it's not as easily accessible as I had hoped. The board which has the connectors is inside the silver casing to the bottom behind the front:
(https://i.imgur.com/OBWixrFh.jpg)
I am afraid that to get the silver casing out I willalso have to remove the PCB for the front control panel, and desolder these two wires, kind of look like they might have been desoldered before:
(https://i.imgur.com/Y2AzIDRh.jpg)
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Here's the front control boar and the board with the BNC connectors.
(https://i.imgur.com/O9db8S0h.jpg)
The board with the BNC connectors is enclosed in a welded shut box. I have absolutely no idea on how to get it out. I'm stumped. Break the welds and force the box open perhaps. I can see nuts on the inside that I think are holding the BNC connectors and board to the front of the inside, so I think opening up the box is the ony way to go.
EDIT:
Check the AC/DC switch contacts - that signal could be capacitatively coupled through a layer of dirt
They looked clean as far as I could tell, the inside of the scope looks clean overall.
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No more time last night for anything more so I went to sleep. This morning I started wondering.... Put the soldering iron to the welds and they melted. So looking a little bit better. Going to work now so we'll have to see later. Think I need to go into the city and get some deoxit and electronics cleaner as well. Might as well give all the pots a clean.
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It's pretty common for shielding to be soldered over sensitive stuff like that, it would be highly unusual for it to be welded. Take your time and be careful not to damage anything. Remember that you have two identical channels so you should be able to make comparisons pretty easily. You should have a 1M input impedance, so follow that until it you find where it becomes open circuit.
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One channel not working is quite common in my experience. The problem can be in input attenuators or in the first JFET, usually a dual FET
Usually if it is the attenuator (if your unit has one) it is usually just one of the attenuators and does not affect all ranges.
I do not have the schematics in front of me but these are the common problems usually because someone did not use a 10X probe and fed in too much voltage into DC.
If you can find the first JFET test it with as ohmeter and compare it to the other channel. If it is this problem, it is easy to fix.
Wally
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Aaaahhhhhhh last night left me feeling so horrible...
I opened up my oscilloscope and I opened up the AT board enclosure. I found the error almost at once. An obviously broken solder to the BNC connector well that was a simple fix I thought! I resoldered it and reassembled and... whole scope was acting erractic and weird, I even lost the traces sometimes. Lost the ability to modulate the amplitude (v/div). Was feeling really down, thinking I broke the scope with ESD, I had it on a mat though and I kept touching an earthed metal piece now and then. I was pretty sure I'd gone and ruined something. Went to bed feeling pretty lousy.
Fortunately I got a tip from someone else and I started looking at the ribbon cables. Turns out one of them had broken but looked whole. I soldered in another cable for test and hey it works again! Now I am feeling really satisfied :)
Both channels work identically now, feeding a 3khz sinewave from my computers headphone socket:
(https://i.imgur.com/OFjBJw1l.jpg)
I still need to properly replace that 3-ribbon cable however.
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Great news...
And just think....you did not pay anything extra for the learning experience HA!
Your tenacity is to be lauded..good repair.
Perhaps leaving the soldered in ribbon might be preferable. if it fits nicely. If this unit uses plug in ribbon connectors, they are not always easy to replace.
Now you can use the scope to repair other scopes, since you had so much fun with this one.
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That's great news. This is also a great illustration of the warnings often given about old analog scopes, finding one that is truly fully working is easier said than done these days. It is also a good example of the sort of problems that often come up and how they can usually be repaired with a bit of perseverance. Now if it ever has any sort of problem again you will feel a lot more comfortable opening it up and troubleshooting.
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I have 2 scopes.
An analogue scope I got off ebay second hand for £45.
A USB PC scope I got off ebay for less than £20.
For storage stuff I use the USB scope. I did a lot of DCC model railway work with that and it was great.
For general analogue work I use the other scope.
Had it 10 years now so its paid for itself many times over.
My max working speed is less than 20MHZ usually so this is fine.