Which isolated o'scope for mains SMPS repair? - Page 1
Forum section: electronics / testgear

author: crystallattice
author_rank: Contributor
timestamp: February 15, 2018, 07:19:58 am
content: Hi,I need an oscilloscope for SMPS, VFD and other high voltage repairs, so isolated inputs are a must. I'm looking at the Tektronix THS720 with its isolated inputs.Is this the best option or are there other options like a cheap handheld scope + some isolated differential probes added on for isolation?The THS720 is 20+ years old already and I was wondering if there is anything newer that can replace it or if I should just buy the THS720 and stop looking for anything else? The schematics and service manual for the THS720 is available which makes it more attractive than a similar priced alternative of which these will not be available.It seems the THS720 can range from about $300-800 depending on what version you go for. I was hoping to find something cheaper but also don't want to waste my money on junk and buy again later, but also not invest a lot of money in an outdated piece of kit when something newer/better is available.What would you guys suggest?

author: kripton2035
author_rank: Super Contributor
timestamp: February 15, 2018, 07:26:43 am
content: I found some years ago a used Metrix OX8042 that is just suited for that . you can find some on ebay sometimes, but mainly in europe.there was also the ox8062 with better bandwith.

author: HKJ
author_rank: Super Contributor
timestamp: February 15, 2018, 07:53:27 am
content: Siglent has some handheld isolated scopes, I do not know how good they are:http://www.siglent.com/ENs/pdxx.aspx?id=93&T=2&tid=2

author: tautech
author_rank: Super Contributor
timestamp: February 15, 2018, 08:04:46 am
content: Quote from: HKJ on February 15, 2018, 07:53:27 amYeah.....nah !For the OP's needs he should get a 4 channel scope......but if he's serious about it, it won't stop there.100:1 probesDifferential probes $ $Current probes $ $ $And maybe a Power Analysis option for the scope too. $ $ $

author: BravoV
author_rank: Super Contributor
timestamp: February 15, 2018, 08:22:21 am
content: Quote from: crystallattice on February 15, 2018, 07:19:58 amWithout upper budget limit, this discussion is meaningless and pointless.As people will start to bombard you by suggesting tons of various products without concern the depth of your pocket.

author: BravoV
author_rank: Super Contributor
timestamp: February 15, 2018, 08:33:08 am
content: Regarding Tektronix THS72xx series, we have a huge thread on it, and hacking too, that turns the low end model into full featured top end model, and free bandwidth upgrade too.Imo, the Tek THS72xx series, even its 20+ years old, the price for used ones are still quite high is for a reason.

author: capt bullshot
author_rank: Super Contributor
timestamp: February 15, 2018, 08:50:49 am
content: If you can find one for a reasonable price, I'd prefer the TPS2024 (or one of the other TPS 20xx models) over the THS7x0 - it's colour screen and way more easier to operate, more responsive. The TPS series has the same isolated inputs as the THS series, swappable internal battery, basically all the features but better. Still very small sample memory, even the latest modern ones have 10k (or maybe 20k) samples only.BTW, IMO the power analysis option (THS720P) is pretty much useless (line frequency only, and slow as molasses). Didn't check this option on the TPS2024.

author: crystallattice
author_rank: Contributor
timestamp: February 15, 2018, 09:15:56 am
content: I thought I mentioned that the THS720 was around $300-800 so that is roughly where my budget lies, or less...The TPS2024 and the SHS1062 are more than double the THS720 price, and then you still have to buy the fancy probes!So the THS720P is not worth it? rather buy a THS720A and upgrade it? Recently bought a Flir E4, and upgraded it, nice when these options are available!

author: capt bullshot
author_rank: Super Contributor
timestamp: February 15, 2018, 09:27:39 am
content: QuoteTHS720P is the same as the THS720A. You'll just have to change an internal jumper to make the "P". IMO it's not worth the effort.QuoteThese are proper isolated scopes, not "just open the earth wire" floated scopes. Voltage applied to the input BNC shell will not appear anywhere else on these scopes, and the channels are isolated per channel. If you use the proper probes (with the isolated BNC connectors), you're safe within the specified limits.If used properly, they can do a way much better job than a diff probe, especially for floating small signals.

author: BravoV
author_rank: Super Contributor
timestamp: February 15, 2018, 09:29:15 am
content: Quote from: blueskull on February 15, 2018, 09:17:12 amIf you mean the Tek THS7xxx series, how ?Its designed from ground up to be float scope "AND" isolated.From the manual ...You just can NOT do with your ordinary scope like this ... but the Tek is designed to be used like this example condition.

author: BravoV
author_rank: Super Contributor
timestamp: February 15, 2018, 09:34:12 am
content: Quote from: capt bullshot on February 15, 2018, 09:27:39 am+1An example of the Tek THS7xxx , watch the BNC probe's inputs, no exposed metal at all.

author: tautech
author_rank: Super Contributor
timestamp: February 15, 2018, 09:34:51 am
content: Quote from: crystallattice on February 15, 2018, 09:15:56 amI'm unsure about SHS1k probes.The online images suggest they come with good HV probes but there's some inconsistencies listed between standard accessories and optional.If they come with the PB925 style 10x probe:Safe voltage levels: CAT II 1000 V, CAT III 600 VFrom the datasheet, confirmed:Two special 10:1, CATII 1000V, CATIII 600V, 100MHz oscilloscope probesObviously the PB925 are the optional 250 MHz probes.At least these HH's have a reasonable amount of memory depth, sure only 2Mpts but that's a heap more than the Teks.

author: BravoV
author_rank: Super Contributor
timestamp: February 15, 2018, 09:55:03 am
content: Quote from: crystallattice on February 15, 2018, 09:15:56 amWhen it comes to isolated "AND" floating scope, its always expensive, even used.Should you decided to pick THS7xxx series, watch out for the isolated probe, as usually the one that included with original probes is much more expensive than the one without any probe or with some random grabbed ordinary one.As the standard isolated probe is fully isolated with no exposed metal, watch closely the BNC connector below, its fully encased in a strong black plastic, while ordinary scope's probe usually have some sort of metal part exposed.It will become pointless, if you bought this expensive scope but used with a probe that with exposed metal parts, as this defies the original purpose to have the protection, so be careful before deciding it.

author: crystallattice
author_rank: Contributor
timestamp: February 15, 2018, 10:22:13 am
content: Yeah, the isolated probes are expensive!Whats the difference between the P5102 and the P6117 probes?It would appear that the THS720 is the scope that I should get/can kind-of afford.

author: crystallattice
author_rank: Contributor
timestamp: February 15, 2018, 11:02:40 am
content: Just found a TPS2024B 4ch locally for about $1300Waiting to hear what probes it has...A bit more than I was planning on spending but maybe this is more worth it, than the THS720 for around $300-800?

author: capt bullshot
author_rank: Super Contributor
timestamp: February 15, 2018, 11:43:15 am
content: Used scopes most often come without probes.< $1000 IMO would be a real bargain on a TPS2024B (without probes), if I was in the need of one, I'd rather buy the TPS2024 for $1300 than a THS720 for $300.The user interface of the THS is really annoying ... plus 4 channels instead of two, 200MHz BW and a decent colour screen instead of a lousy B/W LCD. And I like the TPS form factor more than the handheld THS. Annoying with both is their external wall wart / power brick.At work, I've used both (TPS2024 and THS720A), I'd never touch the THS if I can get the TPS.

author: JPortici
author_rank: Super Contributor
timestamp: February 15, 2018, 12:49:04 pm
content: I agree. the TPS was built with this specific application in mind (altough we use ours to probe high and low voltage sensors in cars)Four isolated channels are very nice! and battery operation!!but i wish there were more options.. this scope is just another ancient, very noisy tek which is still being sold (i think the only difference between variants is that the CF card slot was replaced with USB at some point)I suppose other manufacturers prefer to sell differential and current probes

author: Hydron
author_rank: Super Contributor
timestamp: February 15, 2018, 01:47:50 pm
content: Testec do some fully insulated probes, see here under "Probes for battery-powered Oscilloscopes SP Series":http://www.testec.de/en/products/product-categories/standard-probes/The same probes also seem to be available from Multi-Contact - no idea who is the actual manufacturer:http://ec.staubli.com/products/hfline/1Prices from RS for the insulated probes start from about 40GBP (e.g.https://uk.rs-online.com/web/p/oscilloscope-probes/5180971/)

author: nctnico
author_rank: Super Contributor
timestamp: February 15, 2018, 06:23:57 pm
content: Quote from: crystallattice on February 15, 2018, 07:19:58 amIMHO the main problem is that scopes with isolated inputs are also very limited when it comes to features because they are geared towards field/mobile use. I would recommend to get a regular scope and differential probes.

author: mos6502
author_rank: Frequent Contributor
timestamp: February 15, 2018, 08:20:31 pm
content: The Fluke 190 series has input channels that are fully isolated from each other. Also, the scope is rated CAT III 1000V and CAT IV 600V. If you're working on live circuits and your life is worth anything to you, that's what I would use. They're a bit pricy though.

author: artag
author_rank: Super Contributor
timestamp: February 15, 2018, 10:16:49 pm
content: Or you can float the power supply with an isolating transformer.Much easier.

author: schmitt trigger
author_rank: Super Contributor
timestamp: February 15, 2018, 10:29:52 pm
content: A good insulation transformer. Some ITs have so much interwinding capacitance that at the switching frequencies they allow hundreds of milliamps of leakage.Thee way the windings are arranged, plus any shielding, will determine how much leakage one gets.

author: crystallattice
author_rank: Contributor
timestamp: February 16, 2018, 06:28:32 am
content: Thanks for the input guys!I am concerned by spending all that money for a "special purpose" scope but I also have an old CRT scope(s!). I have used these with the earth disconnected and also with a isolation transformer but feel like the proper thing is in order, besides I do not own a digital scope although I have access to them.The chap with the TPS2024B has not replied so not sure if it is still available, seems like I have to wait a bit and keep my eyes peeled.

author: tautech
author_rank: Super Contributor
timestamp: February 16, 2018, 06:45:54 am
content: I just remembered this thread for you to get a closer look at the SHS1000 models:https://www.eevblog.com/forum/testgear/review-siglent-shs-1602-isolated-scopemeter/

author: BravoV
author_rank: Super Contributor
timestamp: February 16, 2018, 07:11:09 am
content: Or an alternative, find an used Tektronix probe isolator, basically this gadget turns your ordinary scope's probes into a fully isolated and floated ones.At the market, these used isolators are "relatively" much-much cheaper than a full blown used isolated scope you're looking for, but alas, it has the same problem as we discussed before, as it came with its own special prorietary isolated probes standard accessory, so if the seller doesn't include it, again, then probe isolator will become an expensive paper weight.As an hobbyist, I had been thru the path like yours actually, in the search of scoping mains related signal, and at some gadget, I had to wait for years to get a decent priced one, so I think I can feel your pain.

author: crystallattice
author_rank: Contributor
timestamp: February 16, 2018, 08:14:21 am
content: Thanks BravoV,A crappy scope with a fancy gadget attached is , well , just that!I'll have a look at the gadget you mentioned and then also look for a cheap digital scope/portable scope. What did you end up going for The THS720?PS. the TPS2024B is still available, but only has generic probes. He is planning on getting some standard Tektronix probes but I told him rather not let me get the high voltage ones. Still negotiating.....Would standard 10:1 100:1 probes not also "work" if you are willing to "live on the edge"?

author: BravoV
author_rank: Super Contributor
timestamp: February 16, 2018, 08:55:49 am
content: Quote from: crystallattice on February 16, 2018, 08:14:21 amLOL, yeah, but beware though, these ancient Tek probe isolator is gigantic, here the one I scored last year, I just let the photo speaks for it self, comparing to common current cheap DSO size. Its like the probe is swallowing it's own scope.Luckily it works as expected, love it very much.Quote from: crystallattice on February 16, 2018, 08:14:21 am4 years ago I scored a THS710A with complete accessories, actually I made a questioning thread for it during the bargaining period ->HERE.Quote from: crystallattice on February 16, 2018, 08:14:21 amSuggesting to be careful for such expensive "used" stuff, isn't this way over your budget ? My worry is as its used, the risk of its not working properly or out of cal. If that is local offer, if possible, do a physical verification. For me personally, able to do a physical verification worth 10 to 20% of the price rather than buying it online relying just on the photo and the seller's claim.Regarding isolated probe, well, if you're willing to bet on it, here, Aliexpress's grade probe, these are just examples, there are many same offer there. Its all fully isolated with no exposed metal at all.Price wise, these probe is relatively cheap imo, say compared to 1st tier branded ones.P2301C Probe 100:1 High Voltage Withstand 5KV 300MHzhttps://www.aliexpress.com/item/1PCS-wholesale-P2300C-Oscilloscope-Probe-100-1-High-Voltage-Withstand-5KV-300MHz-for-oscilloscope-Tektronix-HP/32352684108.htmlP2301B Probe 10:1 BNC protective cap DC-300MHzhttps://www.aliexpress.com/item/Authentic-1PCS-P2300B-Oscilloscope-Probe-BNC-protective-cap-DC-300MHz-Scope-Clip-Probe-300MHz-For-Tektronix/32352680753.htmlHope this helps.

author: crystallattice
author_rank: Contributor
timestamp: February 16, 2018, 09:18:30 am
content: Wow, that probe makes your scope look like the accessory!Spoke to the TPS scope guy and he is also collecting test equipment for his hobby but sounds like he settled on Fluke 190 so selling the Tektronix, he has offered to bring it along next month when he is in my area so I can test it. Not sure if it will still be available though....Thanks for the probe links. I have bought a set of test leads from the same "brand" and they seem quite decent, at least for what you pay. Unfortunately I had a bad run in with Aliexpress a while back so staying clear from them. Ebay buyer protection is at least fair!

author: capt bullshot
author_rank: Super Contributor
timestamp: February 16, 2018, 11:15:35 am
content: Quote from: crystallattice on February 16, 2018, 08:14:21 amAs far as I know, the TPS2024 has standard probes (10:1) when delivered. The high voltage isolated ones have to be bought extra (e.g. the P5120 20:1 ones). Any probe that you can compensate will work with the TPS2024 (as with any other oscilloscope). The user interface (and all the other features) of the TPS2024 is quite similar to the TDS2024 (non-isolated) series, so you'll get a "normal" DSO with the additional isolation feature.

author: David Hess
author_rank: Super Contributor
timestamp: February 16, 2018, 06:44:15 pm
content: Quote from: mos6502 on February 15, 2018, 08:20:31 pmThe older Fluke Scopemeters can be had for reasonable prices. Usually the only problem with them will be worn out batteries.The LCD displays they have are not very good but are usable and they support peak detection making them a reasonable DSO if you cannot have something with a better display.One of their advantages is that they also make pretty good multimeters.

author: shakalnokturn
author_rank: Super Contributor
timestamp: February 16, 2018, 11:53:21 pm
content: On the paper the Chauvin-Arnoux/Metrix Scopix III or Scopix IV look really overkill handheld scopes: Up to 4x 300MHz, 2.5GS/s, 12bit ADC.No clue how good the user interface is though, that is a detail that can ruin decent hardware.http://www.chauvin-arnoux.co.uk/sites/default/files/D00SAK91_16.PDFhttp://www.chauvin-arnoux.co.uk/sites/default/files/HLHBDYSZ_0.PDF

author: crystallattice
author_rank: Contributor
timestamp: February 19, 2018, 09:02:53 am
content: hi,The Chauvin-Arnoux/Metrix Scopix does look pretty impressive but I think the price tag will put me off a bit, secondhand they are already expensive! Also, it seems they are sold under different names...The chap with the TPS2024b has agreed to $1000 without fancy probes (just 4 generics). The question now is how to properly test the scope? The warranty sticker at the back has been broken so not sure if it was opened/repaired/calibrated or just accidentally broken?Scope comes from a cell repair shop that went bust and an employee bought it on the auction, or so the story goes.So are there any quick tests that one can perform with limited tools to verify the integrity of the scope? I'm not talking about calibration accuracy, but just make sure everything is functioning as it should?

author: capt bullshot
author_rank: Super Contributor
timestamp: February 19, 2018, 10:26:09 am
content: You can check basic functionality by measuring the "Probe Comp" signal with each channel, using the supplied probes. This should display a nice rectanglar waveform, if the probes are properly compensated. Just connect one probe to channel 1, and probe this signal, adjust the scope for a stable waveform, if the waveform does not have clean edges, try to adjust the probe compensation. Then move the probe to CH 2 and repeat. You should also check all probes this way.Then search the "error log" and "self test" (or "self cal") within the menus, and check those.

author: crystallattice
author_rank: Contributor
timestamp: February 19, 2018, 12:11:42 pm
content: Will check error log, didn't know it existed.How "accurate" or reliable is the self test? Is this what the factory uses on the assembly line before they ship it....

author: Fungus
author_rank: Super Contributor
timestamp: February 19, 2018, 12:32:55 pm
content: Quote from: crystallattice on February 19, 2018, 12:11:42 pmOscilloscopes aren't multimeters. Their main use is to see wiggly lines on screen, you can only expect accuracy of a few percent in readings.Quote from: crystallattice on February 19, 2018, 12:11:42 pmYes.

author: Fungus
author_rank: Super Contributor
timestamp: February 19, 2018, 12:44:34 pm
content: Quote from: capt bullshot on February 19, 2018, 10:26:09 amSorry, no. Each probe should be calibrated for a particular channel. You should only connect a probe to the channel it was compensated for. Most probes come with little colored rings to put on the plug so you know where they're supposed to go.

author: forrestc
author_rank: Unknown
timestamp: February 19, 2018, 01:16:03 pm
content: Since this thread is still alive:Quote from: crystallattice on February 15, 2018, 07:19:58 amI've recently become a big fan of differential probes, and specifically the EEVBlog HVP-70's that Dave sells. But I'm using these on a bench with a fixed oscilloscope, not sure if you really are looking for something portable - dealing with the separate probe box and batteries or power supplies would be a pain in a mobile situation.-forrest