Another beginners oscilloscope question! Sod all storage space - Page 1
Forum section: electronics / beginners

author: jewelie
author_rank: Regular Contributor
timestamp: June 04, 2016, 07:51:38 pm
content: Eh up!So sorry to be posting a meter/'scope question, but I've been hunting around this and other forums and watching Dave's videos on the subject and I think I'm just going around in circles. I could really do with informed opinions on my situation.I'm getting back into electronics now. I scraped through a Comp Sys Eng degree over 20 years ago mainly based on my already acquired computing knowledge (bad time of life, had a bit of a breakdown, wasn't helped by a degree that really ought to have been spread over at least 4 years and not 3 if it was going to cover so many subject areas!) My EE knowledge is pretty basic, but I'm probably differently newbie to many others here (i.e. I've used oscilloscopes in a little in the past whilst doing the degree and have always owned a soldering iron and a meter - side effect of having been brought up by a Dad who was a Sparky.)I glad to say that I'm learning and advancing at quite a rate of knots now, so much faster than I ever did first time around; I think this is a mixture of age, different attitude, lack of pressure to learn, the ease of access to fantastic tools, resources and information (especially this forum and Dave's videos - *thank you* everyone), and the reduced entry costs for electronic kit projects and non-critical components (*thank you* China!)I think I'm reaching the point where I could do with an oscilloscope soon, to assist with repairing things, understanding circuits and seeing real world outputs, possibly matching against LTSpice simulations of things (for reassurance/learning.)I would *relish* having my own analogue CRO - it was one of those things I always wanted to have but could never have justified until now. I'm aware that Dave's opinion is that the best budget option is to get a 2nd hand eBay one. That sounds really good to me, too!The problem is this-^^^ That. That's my lab, my equipment, andthat's *all* the storage space I have. Okay, there's more boxes behind those, and another couple (with the regular tools in) elsewhere where my partner can get at them. No cupboards we can clear out, no garden, no spare room, no shed, etc. And no, moving isn't an option either.When I geek out, spread the boxes on the bed, make some space on the desk etc, do my thing, it all has to disappear afterwards.Space issoshort that I ended up getting a budget small Windows 10 tablet to browse, do LTSpice circuits etc on, whilst I learn because I can't otherwise fit the electronics gubbins I'm working on AND our old laptop on the desk!I know general opinion is against based Pocket DSOs, PC DSOs. I can't afford nor justify £100s on a modern, thin-ish DSO. But, 2nd hand oscilloscopes that I've seen so far are*big*, relatively speaking.*BUGGER*SO... What do I do? Does anyone have any thoughts?Do I really need an oscilloscope?(Possibly not *just* yet, but I'm getting there I think.)Is there a common old CRO often on eBay etc that's actually really small and/or easy to hide away?(I've seen references to the Hitachi 212 but that still looks bloody huge.)Are there any acceptable alternative compromises?(Often discussed is Hantek 6022BE + alternative software, or Owon VDS1022? I see the Velleman HPS10 go for £30 / US$50 on eBay - something that small might have the advantage of getting used lots as it'd be easy to get out and put away)?Do I just hang it and accept that I'm going to have to find some space under those boxes for an analogue scope (even if it means my partner will bloody kill me and even if being hidden away means it's a pain to get out and set up!)Sorry, I know this is a tricky one (if it wasn't such a tricky one I wouldn't need to post on a forum to ask for advice!)RegardsJuliexxxModerator note: smiley removed from topic title as it invalidates the link in emails.

author: tautech
author_rank: Super Contributor
timestamp: June 04, 2016, 08:20:25 pm
content: Daves recommendation for a CRO as a first scope was mainly for cheaper entry into scope ownership. It also has the advantage of learning and understanding the traps for newbies: triggers, attenuation, graticules and so on.That you have some experience helps and in your predicament probably a USB scope could be the way to go.They've always scared me as my PC's/laptops are more valuable than an entry level DSO should a fatal (to a PC) mistake be made.Most of the entry level DSO's are smaller than a shoebox and ~2.5 kg (5lb).

author: woodchips
author_rank: Frequent Contributor
timestamp: June 04, 2016, 08:39:26 pm
content: I listed some FOC Gould OS300 analogue scopes a little while back. No interest at all, only rained a few times since so might still work after being chucked in the scrap pile.Space huh, what about the 3' at the top of the wall, lots of shelf space there.Many years ago I came across an old chap who was into model engineering, steam locos and similar. Snag was he now lived in a home, and the concept that the residents could actually do things they wanted to do hadn't arrived. He got a bureau and fitted a small lathe in it, close the lid and no one guessed. He was happy, the home were ignorant. Might be some mileage there but any CRT scope will be 15" or more deep, problem, don't even think of a Tek 7000.Have a Fluke 123 I am trying to get the battery to work. Horrible thing, doubt it has 20 hours on in the 25 years since buying it.

author: jewelie
author_rank: Regular Contributor
timestamp: June 04, 2016, 08:46:22 pm
content: Quote from: tautech on June 04, 2016, 08:20:25 pmYes, I'd have a heart attack if I took out the PC (still recovering from the supposedly decent quality PSU in it blowing a short across the mains - although I've learnt that that was probably a purposeful "crowbar style" failure mode and took out the internal fuse so I probably shouldn't be too critical.) Our laptop is ancient but we both now love it after it's processor, RAM and SSD upgrade (was unusable before though!)The tablet was £50, 2Gb RAM, quad core Intel CPU, Windows 10. That's about the same price as the entry level USB 'scopes and would possibly work on it. It turns out that it has two USB ports too (I thought the micro USB on it was just for charging but I'm writing this via a wireless USB mouse/keyboard connected via a USB OTG stuck in that port.) IF the USB scopes are bareable it would certainly be a very space efficient solution. (But I always wanted an excuse to have a REAL CRO!Lol.)

author: tggzzz
author_rank: Super Contributor
timestamp: June 04, 2016, 08:58:48 pm
content: Consider using a scope at a local backspace, e.g. Nottingham. They would also be a good source of help and encouragement.Failing that, I expect to be selling a working Tektronix 465 and a working HP1740a in the near future. I don't know whether that will be at a hamfest, or on eBay, or privately.Whatever you buy will depend on what you want to do with it. Personally I wouldn't bother with anything less than a 100MHz bandwidth, since that is the minimum to begin to show signal integrity problems in logic systems. If you are only interested in audio or mechatronics, then a lower bandwidth might be OK.Don't forget the cost of probes, and IMNSHO a beginner should only buy a working scope.

author: jewelie
author_rank: Regular Contributor
timestamp: June 04, 2016, 09:01:46 pm
content: Quote from: woodchips on June 04, 2016, 08:39:26 pmOr even better the Gould OS300 scopes might be slightly faulty and respond to a bit of repairing, lol? (Sorry, just had the buzz the last few weeks relating to successfully repairing a couple of Fluke DMMs, one slightly bashed up, one completely b*ggered. I think that means I'm now due a complete failure with the next thing I attempt to repair.) If you think either work or would be repairable I'd certainly be interested?You're right though. Although I can't really put anything on the walls (it's the bedroom) there's probably some options for a CRO if I attack this solution a bit more laterally and creatively, like rigging up something under the desk or chatting nicely with my better half to try to persuade her to get rid of some more junk (so I can have more junk. :-p ) It might have to be that I agree to her having more junk so that I can also have some more junk. ::wince:: LOL.

author: tggzzz
author_rank: Super Contributor
timestamp: June 04, 2016, 09:24:21 pm
content: Caution. The first CRO I repaired required me to faultfind waveforms at -2.75kV.

author: rstofer
author_rank: Super Contributor
timestamp: June 04, 2016, 09:41:52 pm
content: Woeking within its limitations, I would highly recommend the Digilent Analog Discovery. In a package the size of a pack of cigarettes, you get a two channel scope, two channels of arbitrary waveform generator, voltmeter, 16 channel digital IO usable as a logic analyzer and a couple of adjustable power supplies.Nope, it's not free or even close. But it is small, highly capable and would work well with a tablet. I have it installed on my Surface Book. I would be very careful about testing unknown voltages with the device hooked up to something as expensive as a Book! The vast majority of my hobby interests run in the 5V range, more often 3.3V I'm not out probing 'mains' stuff, even with a real oscilloscope.http://store.digilentinc.com/analog-discovery-2-100msps-usb-oscilloscope-logic-analyzer-and-variable-power-supply/

author: G0HZU
author_rank: Super Contributor
timestamp: June 04, 2016, 09:55:07 pm
content: The Hameg 1004-3 is a fairly small and modern 100MHz CROhttp://www.testequipmentdepot.com/hameg/pdf/hm1004-3_manu.pdfW 285mmH 125mmD 385mmWeight 6.5kgThis is smallish and quite light for a modern CRO but it is still quite deep. I've got one here salvaged from the skip at work and it's quite a pretty scope although I really don't like the user interface. Not sure what it's worth but NOBODY else wanted it at work. This should tell you that this type of scope has very limited appeal even if they might fetch £50 or more on ebay.Also, unless you are going to be doing lots of old school radio based work then this type of scope probably isn't right for your needs. The vast majority of hobbyists would be better off with a decent USB scope or the Analog Discovery as mentioned above. Better still would be the Rigol 1054.Why not buy a cheap USB scope for the short term and then save up and buy the Rigol at a later date if you find you need to go up a class in oscilloscope?

author: G0HZU
author_rank: Super Contributor
timestamp: June 04, 2016, 10:05:40 pm
content: For completeness, I also salvaged one of these Hameg CRO scopes from the company skip.HM1007 100MHzhttp://www.radiomuseum.org/r/hameg_analog_digital_oscillosc.htmlThis is an analogue/digital combi CRO scope that is slightly bigger than the HM1004 and it can do some basic storage and I much prefer it to the little HM1004-3. It's quite old though.But once again, NOBODY else wanted it at work. I might keep this one as a reserve CRO scope in case my old Tek 465 ever goes BER.The digital storage capability elevates it to 'tolerably usable' if you wanted to do some basic AVR/PIC MCU based work and wanted to look at serial data etc. A basic CRO would be close to useless here. However, the other USB or DSO options are going to be vastly superior here.

author: tggzzz
author_rank: Super Contributor
timestamp: June 04, 2016, 10:38:01 pm
content: Quote from: woodchips on June 04, 2016, 08:39:26 pmThat mirrors what I can see. My local hackspace is often given 20MHz scopes; now we'll only even consider them if they are working.

author: tautech
author_rank: Super Contributor
timestamp: June 04, 2016, 11:00:55 pm
content: Quote from: jewelie on June 04, 2016, 09:01:46 pmSeriously *don't * go there.Yes you're hooked on fixing stuff now and it's great to see especially in a woman.However when I read your posthttps://www.eevblog.com/forum/repair/fluke-87-(original)-product-flaw-l10a-socket-detect-input-alert/msg955286/#msg955286and your apprehension of working with *even* comparatively low voltages you'l be well out of your comfort zone fixing a CRO.Furthermore repairing CRO's is not straightforward and often another scope is needed to diagnose faults.Set your sights on a basic USB scope or a combo unit as rstofer suggests for now but with a target to get a DSO as funds permit.

author: mtdoc
author_rank: Super Contributor
timestamp: June 05, 2016, 03:58:11 am
content: Quote from: rstofer on June 04, 2016, 09:41:52 pmYes. This. Exactly!The size/features/performance/price ratio cannot be beat.

author: tggzzz
author_rank: Super Contributor
timestamp: June 05, 2016, 07:26:32 am
content: If you want averybasic scope, this one is available in Ilkeston:https://www.gumtree.com/p/other-radio-equipment/telequipment-d61a-10mhz-oscilloscope/1172155304If nothing else, it might help you understand what youreallywant/need.

author: jewelie
author_rank: Regular Contributor
timestamp: June 05, 2016, 01:26:33 pm
content: Quote from: tautech on June 04, 2016, 11:00:55 pmYou are absolutely right. After writing that post I realised how stupid I was thinking that: diagnosing DC-type faults at low voltages is in no way comparable to dealing with HF AC issues and high voltages, and as you say even if I had "teh skillz" I'd probably need at least a decent scope to stand a chance in hell of fixing one.

author: jewelie
author_rank: Regular Contributor
timestamp: June 05, 2016, 01:48:06 pm
content: Quote from: tggzzz on June 04, 2016, 08:58:48 pmExcellent point! I've been horridly ill with Crohns disease for the last year or two, which has kept me pretty darned housebound throughout that time, and I had pretty much completely forgotten about the social angle to this, which is ironic given that it was due to the effects others' enthusiasm and can-do attitudes at local geek meet-ups that I slid back into playing with electronics again.Rather luckily, my Crohns is now finally responding to a medication (thank goodness for the NHS) and getting out is a real possibility again, and Nottingham is only one very comfortable, very affordable, 30min coach-style bus ride away.Quote from: tggzzz on June 04, 2016, 08:58:48 pmYes, I've absorbed yours and others responses and know the error of my ways on that: it would need to be working. (I hadn't forgot the cost of the probes, BTW.)I've been having a think what I might want such equipment for, right now, if I had one, rather than just being theoretical-1. I've a printer to try to fix, although it's unlikely fixable by me if it's really a logic-level error.2. I've an intractable issue with a 4-board LED Matrix display connected to a Pi. The display board works most of the time, but after a few hours all four boards stop responding; there's lots of things I can do to try to pin it down (change PSU, check peak current usage again using the Fluke 87s 1ms peak detect range, uprate the PTC, fiddle with the software, read the specs for the Pi's SPI implementation, try to understand the code) but I'm desperately frustrated that I cannot see the signals going to it and I suspect that's where the issue will be (I don't like black boxes, that's why I did the degree I did! I don't even know roughly what frequency it's clocking at.)3. When playing with building AC/oscillating circuits, I really want to be able to see the waveforms - seeing that it appears to work (if it does) isn't really enough.

author: tggzzz
author_rank: Super Contributor
timestamp: June 05, 2016, 01:55:00 pm
content: Quote from: jewelie on June 05, 2016, 01:26:33 pmDon't worry too muchRealising a mistakebeforeit bites you puts you ahead of most of the crowd.I debugged my first scope with a multimeter and mark one eyeballs.The second one was mostly diagnosed with mark one eyeballs and without a scope. Arguably if I had had a scope it would have been diagnosed faster, since I would have quickly pulled the tube and found the broken internal connection. As it was, I faffed around indirectly measuring what was happening in the -2.75kV grid circuit.What isnecessaryis an understanding of how each bit of a scopeoughtto be working, some imagination about how (or if) to measure things, and a knowledge of where the mains/110V/2kV/17kV points are. Some scopes are better than others at keeping the mains and 110V away from fingers.

author: jewelie
author_rank: Regular Contributor
timestamp: June 05, 2016, 02:02:07 pm
content: Quote from: woodchips on June 04, 2016, 08:39:26 pmA rather positive update.... had a chat with my parter, who has been a bit of a junk-hoarder for years. She surprised me and, touch wood, was up for a mahooosive clearout and re-arrange.No Space + A reformed hoarder + 4 hours - 3 Large Bin Bags of junk = SPACE!(In fact, afterwards, too much space, lol. Had to fill it up a bit to not look to bare.)There's at least two lots of 19" x 14" x 22" gaps I can use there.I imagine I could fit an old scope there facing left, towards the desk where I do stuff? I can even cover it over when it's not in use to make it look more like a bedroom again.Juliex

author: tggzzz
author_rank: Super Contributor
timestamp: June 05, 2016, 02:07:41 pm
content: Quote from: jewelie on June 05, 2016, 01:48:06 pmIn an ideal world, I would use a >100MHz scope to ensure there are no PSU integrity, ground bounce, and signal integrity problems, and then use a logic analyser to capture your signals.The third scope I fixed had a common problem that manifested itself in an "interesting" way. When first turned on in the morning, it would take 1-2 minutes to start up. When turned off and on, it would start up instantly. Hence I could do one test every 6 hours, looking for an intermittent problem. That required a storage scope; I used my Analog Discovery.Note that an Analog Discovery contains two 10MHz scope channels (with FFT in software), two 10MHz AWG function generators, a 16 bit 100MS/s pattern generator and a 16 bit 100MS/s logic analyser. They can all be tied together to form a spectrum analyser, a network analyser, a control-loop analyser. It is also very small and you have to be careful of the voltages you apply.

author: jewelie
author_rank: Regular Contributor
timestamp: June 05, 2016, 02:09:53 pm
content: Quote from: tggzzz on June 05, 2016, 07:26:32 amThanks for that. I've mates in Ilkeston who'd probably help me collect it too. £10 for something that although very basic is supposedly also very serviceable and doesn't take up much space might be handy, even if just as a learning opportunity, so I may give them a call and chat about it.

author: jewelie
author_rank: Regular Contributor
timestamp: June 05, 2016, 02:15:20 pm
content: Quote from: tggzzz on June 05, 2016, 02:07:41 pmHmmmm..... it sounds like, for that, I probably want to take the Pi & displays to a hackspace then; better equipment, more (and more experienced) minds?Are oscilloscope probes pretty standard? If I got some nice new probles to use with a really old scope would I still be able to use them on newer scopes (i.e. are the probes a logical place not to trim corners)?

author: GreyWoolfe
author_rank: Unknown
timestamp: June 05, 2016, 02:40:04 pm
content: The probes should at least be rated the same as the scope-100MHz probes for a 100MHz scope. You can use them on a lower bandwidth scope also, just not higher. For basic hobbyist use, the China probes are cheap and usable.

author: jewelie
author_rank: Regular Contributor
timestamp: June 05, 2016, 02:44:10 pm
content: Quote from: GreyWoolfe on June 05, 2016, 02:40:04 pmYou mean the China "P6100" ones? I noticed they were reviewed relatively positively in other posts. There's someone selling them in the UK in pairs for same price as delivered from HK, so might be worth me just buying those now so that if I get cheap old CRO I'll be able to see it working ASAP.

author: tggzzz
author_rank: Super Contributor
timestamp: June 05, 2016, 03:30:13 pm
content: Quote from: GreyWoolfe on June 05, 2016, 02:40:04 pmBe careful, there's ratings and there's specifications.Many 100MHz probes are 3dB down at 100MHz, so with a 100MHz scope the combination would be 70MHz. Others are "for use with a 100MHz scope", which presumably means the combination would be 100MHz.

author: tggzzz
author_rank: Super Contributor
timestamp: June 05, 2016, 03:42:00 pm
content: Quote from: jewelie on June 05, 2016, 02:15:20 pmI have no idea what equipment they have, but I would expect they havesomeexperience.QuoteYou can get new probes from £10 to >£10,000. Tektronix have just introduced probetipswhich cost you £5 every time theytoucha circuit!Seehttps://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/for references about choosing and using probessafely. For you, the key points will be the safety issues, the types of probe, and the ground connection.QuoteModern professional probes contain their own calibration, and inform the scope of it when they are plugged in. Clearly those aren't completely portable between scopes!However, for your purposes, old probes and equipment they can be mixed-and-matchedprovidedthe probe's "compensation range" encompasses the scope's input capacitance. A dodgy probe can ruin your measurements, but I doubt it is worth you spending much money on them - for now. You'll know when you have to spend more

author: woodchips
author_rank: Frequent Contributor
timestamp: June 05, 2016, 04:32:40 pm
content: Looks like this is moot, but pulled the bottom OS300 from the pile and after a day in the sunshine works ok.Finished charging and cycling the Fluke 123 battery and definitely naff, scope works ok though on the charger.

author: jewelie
author_rank: Regular Contributor
timestamp: June 05, 2016, 09:01:17 pm
content: Quote from: tggzzz on June 05, 2016, 07:26:32 amIt was from RF pros who have a family run business, son & father, who do installs and maintenance of radio transmitters. It even came with the manual, including schematics and calibration instructions (it will need a bit of a calibration I think.)Turns out where they lived was on the bus route just nearest where I live, and they had a stop outside their door. The £10 was worth it just for the time spent chatting (was 2hrs until the bus home) and a look at their equipment (a *lot* of nice equipment in a small space, lol, seems to be a common thing.)Made new friends and discovered there's a big local Radio Rally coming up next weekend (and there's a bus from right outside where I live all the way there to it.)Mind you, I had a sad for ten minutes when I got home and couldn't get it working again (they demo'd it to me before so it was definitely working.) Could not get traces on the screen for far too long.... hadn't noticed that the trigger level knob pulled out to set to auto mode, doh. It needs a little calibration, but it definitely works! I know it's only 10M but I think it'll be fun playing with it if nothing else and, as you indicate, it'll give me an idea what I want to do with one in future.Been a nice hot sunny day too. Days like this are gold!THANK all.RegardsJulie

author: tautech
author_rank: Super Contributor
timestamp: June 05, 2016, 09:23:18 pm
content: That's a good start.My first scope was it's big brother, a 60 MHz D83 that was manufactured after Tek had acquired Telequipment and were running them as their UK division.They are quite repairable and that old girl is quite likely all discretes, maybe even a few glowing onesI've never looked inside one. Many of the semiconductors in these are getting hard to find and when I had mine I made a transistor substitution list that I've got tucked away should you need it.There's a few TQ manuals online, I'll grab a D61A and have a look for any things you need to be aware of.

author: tggzzz
author_rank: Super Contributor
timestamp: June 05, 2016, 09:48:21 pm
content: I expect they were glad to see it go to someone that will appreciate it.Get some cheap *10 probes from fleabay - make sure the probes's compensation range includes the scope's input capacitance, e.g 15pF-30pF for a 20pF scope.Don't rush into fiddling with the calibration; you can see and understand a lot without it. Get comfortable with how the scope works. (And make sure you know all the locations of the nasty voltages inside the scope!).If you use understanding and imagination, you will be able to use the scope and other test equipment to do more than some (typically youngsters) think is possible.As I told my daughter, "have fun, safely".

author: alsetalokin4017
author_rank: Super Contributor
timestamp: June 05, 2016, 10:37:49 pm
content: Congratulations on your cute scope! Seems to fit in its new home quite well.Here's a pdf version of the Instruction and Service Manual. I've had a quick look at it and it seems very straightforward.http://4hv.org/e107_files/public/1341783999_3414_FT141370_d61a.pdfOne thing to note is the input capacitance of 35 pF. This is the top end of the compensation range of the typical Chinese cheapo probes like these:http://www.ebay.com/itm/Two-P6100-DC-100MHZ-Oscilloscope-Scope-Clip-Probe-100MHz-For-Tektronix-HP-DG-/172050381946?hash=item280f007c7a:g:dhUAAOSwJkJWifXiWhatever probes you decide to purchase, you should make sure that their compensation range goes as high as 35 pF.Enjoy!

author: chris_leyson
author_rank: Super Contributor
timestamp: June 05, 2016, 10:54:02 pm
content: Nice one jewelie, and a lot cheaper than an Analog Discovery. I think you will learn a lot from it as tggzzz said "understanding and imagination". My first scope was a Cossor 339, it would have been three bus trips and a long walk, got my dad to give me a ride, he wasn't impressed, I could see it on his face, you paid how much for that ? I think it was £25 but i weighed 40lb. I learnt a lot from seeing voltages. Glad you've got youself a nice scope.

author: chris_leyson
author_rank: Super Contributor
timestamp: June 05, 2016, 11:06:35 pm
content: Come to think of it, the Telequipment Serviscope Minor was quite cute but useless at the same time, it had a nice warm valve smell anyway.

author: tggzzz
author_rank: Super Contributor
timestamp: June 05, 2016, 11:21:27 pm
content: Most scopes have a "cal" output. Donotpresume the amplitude and frequency are as stated and suitable for calibrating the Y scale and time scales.Thesolepurpose of the cal out is to enable tweaking of theprobesfrequency response, and that only requires a constant amplitude and well-defined fast-ish transitions.

author: tautech
author_rank: Super Contributor
timestamp: June 06, 2016, 01:44:32 am
content: I'd nearly forgotten how nice the manuals are for Telequipment scopes.Principles of Operation is delightful to read and Maintenence & Calibration is nicely step by step and easy to follow.Schematics are very well drawn and not at all cluttered with a nice component finder reference.Just beautiful.PDA is derived from a 1kV winding on the PSU transformer and a discrete doubler. Couldn't be much simpler.No valves other than the CRT in these but the worrying thing is the unspecified 3 FETs listed as F.E.T. TEL. SPEC.They're all N channel and 2 are listed as the same part so if you were unlucky and one of those failed you might be able to match parameters from the other.How to test FET's ....well you'll have to Google that.For the transistors that X-referenced with my old list....as outlined below:BC107 NPN = Available use BC547BC109C NPN = Available Hfe 420-800 use BC547CMPS6518 PNP = 151-0320-01 = 2N5401I've always tried to be careful with transistor selection in CRO's in order to have a small spread of Hfe, easy to do with any of the cheap DMM's that have that functionality.Other semiconductors, well just yell and someone will do the homework for accurate substitution.

author: jewelie
author_rank: Regular Contributor
timestamp: June 06, 2016, 12:18:36 pm
content: Quote from: tautech on June 05, 2016, 09:23:18 pmYou're totally right about it being all discrete components too - there's not a chip in sight. I was looking through the manual last night. They don't make stuff with manuals like this now, do they? Even just the manual is a thing of beauty.It's its own learning experience too, lots of details of the theory of operation; whoever design it was quite proud of their work.I guess it's possible that I might need the subs list at some point in the future if you ever find it again.Things I've already noticed to be aware of-Danger danger, high voltage! If I do open it up I'm going to have to be really careful, but then it's a CRO and I already knew that. There's 1kV coming off the mains transformer that's made into 2.5kV for the tube with diode/capacitor arrangement (forgotten what that's called.) Even the focus knob on the front is actually connected to 110V. Yes, I know disconnecting it from the mains doesn't make it safe, etc.Looking at the circuit diagrams... probe inputs don't seem to be a differential type inputs? Ground is, I think, mains Earth? I don't think there's a whole lot of input protection?

author: jewelie
author_rank: Regular Contributor
timestamp: June 06, 2016, 12:59:50 pm
content: Quote from: tggzzz on June 05, 2016, 09:48:21 pmThese are the probes I've got coming-eBay auction: #181872651104. It didn't make sense to spend much more at this stage than the minimum required. Someone else has pointed out that they're just within the scopes range.Using it's own 0.5Vpp calibration point, the display looks spot on for vertical. Horizontal does seem off. But yeah, I totally don't intend to be opening anything or attempting calibration for some time yet, not least of which if I don't use it a good length of time first I won't really know what it's flaws are.Opening it to calibrate it would be a bit anxiety provoking and I would certainly not do without a long line of precautions (including having someone competent there with me) but may actually do me good - with my Dad having come from a Sparky background he had always drilled in to me the importance of safety but I have, to some extent, done myself a little injustice over the years breeding too much anxiety with regards to higher than about 12V DC and have done too much avoidance -- I'm not unaware of proper procedures when dealing with mains, CRTs etc I just don't willingly risk it unless seriously unavoidable. To use your phrase, rather than "have fun, safely" I've only ever done the "safely" bit and consequently missed out on a lot of fun (that's, sadly, describes far too much of my earlier life!) There's a balance to be struck and I've often got that balance wrong (in the opposite way to most that do.) At University I was surrounded by people who habitually took things apart -- I never took things apart (unless they were definitely "serviceably" broken.) At Uni I've friends who'd do childish things like make capacitor guns out of electrolytics, I'd never do such things. I do NOT like things going bang, thanks, lol. With this oscilloscope there will be gradually higher voltages that need to be faced, going from about 7.5V to 110V (I won't be going anywhere near the 1kV, full stop.) I guess I've been surrounded by mentors who just impressed caution part and assumed people would seek the fun themselves - but that's where I needed, and perhaps still need, encouragement, but I'm getting there...With regards to imagination, I didn't get to the end of the day without wondering and Googling if I could drive it from the Pi or an Arduino as a vector display (it MAY even be possible to wire it up as a real raster display, it has X-Y mode and a brightness input at the back - could it be as simple as a sync separator chip and some appropriate filtering/amplification?)A random aside.... the SPI driven Pi LED Matrix display that I mentioned earlier appears to be working fine for extended periods now I hacked the software to reduce the clock from 0.5MHz to 50KHz (although for short durations at least it seems to work fine at 5MHz too so I'm still not convinced it was just clocked too fast for the dodgy wiring to handle.) I'm already wondering what the data signal would look like on the oscilloscope if I triggered on the chip select, whether I'd manage to get anything steady (don't spoil it by telling me :-P )

author: jewelie
author_rank: Regular Contributor
timestamp: June 06, 2016, 01:05:22 pm
content: Quote from: tautech on June 06, 2016, 01:44:32 amThank you!Ah yes, the Hfe function that Dave says nobody uses, I do have a DMM with a Hfe function and have used it a few times (managed to fry one transistor so far, doh, but also reassuring to see the Hfe staying the same when I just think I might have hurt it.)

author: jewelie
author_rank: Regular Contributor
timestamp: June 06, 2016, 01:10:56 pm
content: Quote from: woodchips on June 05, 2016, 04:32:40 pmTo be fair, I've got a lot of testing of the D61A to do yet, it might be poorly still. (I've not had a clean non-zero signal trace on it yet.) But thank you.Have you read this?https://www.eevblog.com/forum/testgear/fluke-123-scopemeter-and-battery-replacement/

author: AndyC_772
author_rank: Super Contributor
timestamp: June 06, 2016, 01:29:51 pm
content: Quote from: jewelie on June 06, 2016, 12:59:50 pmThe frequency of a scope's cal output can be pretty arbitrary; as long as it's roughly in the right ballpark, it's OK for its intended purpose.If you want to do a quick check of whether or not the scope's time base is remotely accurate, all you need to do is touch the end of the probe, and measure the frequency of the sine(ish) wave that you see on the screen. It should be 50 Hz. (Free time base reference, courtesy of your local electricity supplier!)

author: jewelie
author_rank: Regular Contributor
timestamp: June 06, 2016, 01:46:53 pm
content: Quote from: AndyC_772 on June 06, 2016, 01:29:51 pmHave done, see pic, hence why I know it's a bit out. The Cal signal is derived from the mains too. Both say it's about 30% out from what I can tell!

author: tggzzz
author_rank: Super Contributor
timestamp: June 06, 2016, 02:41:52 pm
content: Quote from: jewelie on June 06, 2016, 01:46:53 pmI haven't read the manual (that's your job), but I wouldn't trust the cal signal. When calibrating the Y axis, I would use any convenient DC voltage source and measure it with a voltmeter. When calibrating the time axis, I would use a cheap crystal oscillator followed by lots of divide by 10 (or even divide by two). For the latter, the RPi's oscillator is probably much better than the scope, and you can probably program some counter/timer chip to give other frequencies. Since it is a 2 channel scope, you can easily verify that you've chosen the desired integer division ratio.

author: jewelie
author_rank: Regular Contributor
timestamp: June 07, 2016, 02:40:05 am
content: Quote from: tggzzz on June 06, 2016, 02:41:52 pmWhen I said I had done I meant that I'd used the Cal to check the timebase/X - as that's just the mains frequency I can be fairly sure it's accurate and the display was about 30% out.I've got a 2.5V Vref IC so I can use that to check the Y when I've got the probes, then, yes, I could probably get the Pi doing some test frequencies.

author: tggzzz
author_rank: Super Contributor
timestamp: June 07, 2016, 07:40:26 am
content: Quote from: jewelie on June 07, 2016, 02:40:05 amThe mains frequency is variable and is a good indicator of the amount of excess generatimg capacity. It can be 0.2% out, which is the same as the scope's accuracy; as I write this it is 49.983Hz or 0.3% out. Seehttp://www.gridwatch.templar.co.uk/for the instantaneous frequency and history. That also has many other interesting measurements, e.g. for the last 3 days the total UK wind output is <10% of peak output and for the last day <3%. That demonstrably puts the lie to the innumerate argument that "the wind is always blowing somewhere".You don't need a voltage that is accurate to <2%. You do need voltage(s) that areknownto <2%.

author: jewelie
author_rank: Regular Contributor
timestamp: June 08, 2016, 02:35:49 pm
content: SHINY ALERT!Leads arrived, so I adjusted the compensation as probes as per the scope's manual and then got the frequency generator software going (https://github.com/JennyList/LanguageSpy/tree/master/RaspberryPi/rf/freq_pi) generating some signals (after hacking out a version to use a lower frequency source base oscillator.)It actually took me *FAR* too long to diagnose why I couldn't get the sweeps working with a trigger. I though it was me having a fundamental misunderstanding about using scopes or the limits of this scope..... then I discovered I'd plugged the ****ing jump lead into the wrong GPIO pin on the Pi (which is, of course, why I couldn't neither see nor lock to the trigger, whatever I did!)It's much fun. Now to work out what to do with it! :-pAlso my Arduino Nano V3.0 clone arrived. I can't believe how flexible that thing is. The size of my little pinky and only £1.50 delivered. So, SHINY!!! x 2.*** THANK YOU FOR YOUR HELP, EVERYONE! ***

author: jewelie
author_rank: Regular Contributor
timestamp: June 08, 2016, 02:38:30 pm
content: Quote from: tggzzz on June 07, 2016, 07:40:26 amSo I could potentially use the Cal signal from this, combined with that page, to check low frequency accuracy of my meters' frequency readings?Quote from: tggzzz on June 07, 2016, 07:40:26 amAh yes.... known and stable more important more useful than accurate but unknown?

author: StillTrying
author_rank: Super Contributor
timestamp: June 08, 2016, 03:43:54 pm
content: List of time stamped UK 50Hz readings.http://www.bmreports.com/bsp/additional/soapfunctions.php?output=XML&element=rollingfrequency

author: tggzzz
author_rank: Super Contributor
timestamp: June 08, 2016, 05:19:28 pm
content: Quote from: jewelie on June 08, 2016, 02:38:30 pmPrecisely. This afternoon I tweaked my new Tek 475's voltage gain from 10V/div to 5mV/div using a bench power supply and multimeter. The service manual said apply 20mV, the bench PSU said it was 20mV but the DMM said 21.5mV. So instead of tweaking it to be 4 divisions, I tweaked the gain until it was 4.3 divisions.It sounds like you are learning a lot! Have fun, safely.