Advice or manual for Goodwill GOS 622 Analog Oscilloscope? - Page 1
Forum section: electronics / testgear

author: alex.martinez
author_rank: Contributor
timestamp: December 27, 2016, 04:58:47 pm
content: Saludos!So after purchasing a cheap broken Hantek USB oscilloscope, and experiencing what kind of crap it is (it burnt the hell out of my USB ports). I decided to go for a second hand analog oscilloscope 20 MHz bandwidth for my Final Degree Project and hobbies. Found one in my area (Spain) where oscilloscopes are quite expensive here and I agreed on 90 € for it with power cord and two probes.It is a Goodwill GOS 622, the point is that it looks a little bit crusty. I tried to look for any kind of manual on the internet but all I find is for an Intek GOS 622G oscilloscope, which is very similar, but from another brand. I would like to read some of the specs before buying it as I only know the bandwidth. The owner claims that he has no manual and I canot find it on the internet. Does anyone know where to find a manual, or knows its specifications? Is it really worth the price? I would really appreciate the help.Here I found the same model on eBay (in German) but again, no manual nor specs on the description:http://www.ebay.es/itm/181515477352?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AITThank you for your help!

author: Fungus
author_rank: Super Contributor
timestamp: December 27, 2016, 05:25:13 pm
content: Bienvenido!20MHz, very basic, green screen 'scope for 90 Euros? Not a good purchase.

author: Gyro
author_rank: Super Contributor
timestamp: December 27, 2016, 05:48:35 pm
content: You should probably be looking at next thread for some tips:https://www.eevblog.com/forum/testgear/old-analog-or-usb-oscilloscope-need-advice/

author: alex.martinez
author_rank: Contributor
timestamp: December 27, 2016, 06:01:22 pm
content: Quote from: Gyro on December 27, 2016, 05:48:35 pmI've already looked for some tips in that thread, found that Intek oscilloscope I was talking about. The point is that I wanted to find the manual for that scope in particular, I want to know what I'm purchasing. I cannot just go to a thread and find an oscilloscope as 90% of sellers won't ship to Canary Islands, so I need to look in the surrounding area for such equipment.Quote from: Fungus on December 27, 2016, 05:25:13 pmIt is what I was fearing. Could you give me areasonable range for that particular kind of scope? I don't want to be one of those annoying newbies asking for help.Thank you in advance !

author: nctnico
author_rank: Super Contributor
timestamp: December 27, 2016, 06:18:29 pm
content: Quote from: Gyro on December 27, 2016, 05:48:35 pmThis thread is also interesting:https://www.eevblog.com/forum/blog/eevblog-954-how-to-setup-an-electronics-lab-for-$300/The USB scope mentioned in there (Owon VDS1022I) seems to have isolation so it shouldn't be able to damage the computer it is connected too.IMHO it shouldn't be hard to order overseas and if an Ebay seller doesn't seem to ship to a certain country it often helps to just ask. In many cases people have no idea which countries they are excluding or including. I always ask if they ship to theNetherlands (West Europe)to hint that I'm residing in a civilised part of the world. The Canary Islands are part of Spain which is also in West EuropeGetting a forwarding address from the US (for example shipito.com which I have used myself) can also make life easier when dealing with US sellers who think there is no world beyond the borders of the US.Anyway I don't think it is wise to sink money in a very old analog oscilloscope. It is very likely to have problems or get them soon.

author: alex.martinez
author_rank: Contributor
timestamp: December 27, 2016, 06:29:59 pm
content: Quote from: nctnico on December 27, 2016, 06:18:29 pmI watched that video before buying the Hantek USB oscilloscope, it's how I got aware that those things existed. I tried to get it from Amazon to the Canary Islands, but the shipping fees are huge. That is one of the reasons why nobody wants to even hear about this part of Spain, it has to be first shipped to the Penisula, and then to the Islands a process that is expensive (if hired a professional curier) or extremly unreliable (if done by the National Post Office). I went with that Hantek because there was a seller already in the Islands.For a standar weight of 10 Kg, the parcel can cost up to 300 €, and that is just unreasonable.

author: Gyro
author_rank: Super Contributor
timestamp: December 27, 2016, 06:48:40 pm
content: Quote from: alex.martinez on December 27, 2016, 06:01:22 pmSorry, that sounded a bit rude in hinsight. I understand your problem (the Canary Islands still sound a bit 'exotic' for some sellers possibly). I don't think you've stated an upper budget limit yet, but assuming you bought the Hantek in the firrst place because it is limited then, yes, the VDS1022I would be a superior, Isolated, alternative. I did a search of ebay.es from your link and there are a couple of sellers in Europe with reasonable postage, but more from China, cheaper and with free worldwide shipping - my Spanish isn't good enough to see any exclusions though. Here's the main teardown thread if it helps...https://www.eevblog.com/forum/testgear/owon-vds1022i-quick-teardown-(versus-the-hantek-6022be)/

author: nctnico
author_rank: Super Contributor
timestamp: December 27, 2016, 07:13:20 pm
content: Go on Aliexpress and you'll find many ship for free worldwide. I can't see any exclusions for the Canary Islands but then again most from Aliexpress is shipped using the local post office by default so count on 4 to 8 weeks delivery time.For example this one is free shipping using China mail or $47 with EMS to the Canary Islands:https://es.aliexpress.com/item/OWON-VDS1022I-USB-Isolation-25MHz-PC-Digital-Storage-Portable-Oscilloscope/32761980300.htmlNote: I don't speak Spanish I just hacked the URL to provide the Spanish version of the page.

author: alex.martinez
author_rank: Contributor
timestamp: December 27, 2016, 07:26:44 pm
content: Quote from: Gyro on December 27, 2016, 06:48:40 pmI should have read your post about the OWON before, it has a better Quality/Cost ratio than the Hantek, and it would have not fried my port. That Hantek had a data cord into the device which then split into two USB to supply the 1 Amp demand. One of those USB terminals was totally open (probed it with a multimeter), so the other USB just drew the enterity of the current from a single port or at least I reasoned so after hours of internet search, it seems to be a recurring problem with the provided cable in that model.Well, my budget is in 100 €, I'm working with biosignals, so I really dont need fancy bandwidths, the needs are satisfied with 20 MHz, some the maximum frequency I would have to deal with are 4 kHz from EEG. I would just like to get a temporal scope to do the job, as when I finish my degree I'm planning on getting some professional stuff. I have designed already a pretty decent amplification and filtering stage, so I would only need a device to give me a taste of what I'm doing.What I've found in my area are two scopes, the one I mentioned earlier (the GOS 622) and an analogue Promax OD - 352 for 80 € (no probes) for which I cannot find the manual. There is an ARAIO AL - 651 A from the 70's which has neither probes nor power cord...so I'm pretty much stuck with that Goodwell GOS.I've been also looking at your OWON recommendation, but it gets out of my budget with shipping, and the experiences I got from importing chinese stuff are not very pleasant, they always get stopped at customs.Thanks in advance

author: Gyro
author_rank: Super Contributor
timestamp: December 27, 2016, 09:09:33 pm
content: Unfortunately, we all have those 'If only...' moments and they do usually occur after something has fried!That's a really lousy collection to have to choose fromI don't envy your position (or location!).I've managed to find the a manual for the GOS-662. There's no service information, just a block diagram, but I doubt if there's anything very challenging inside. I've never heard of either Promax or the ARAIO.http://www.eserviceinfo.com/downloadsm/21726/GoodWill_GOS%20622/623.htmlThe listing just shows a flat line trace, so no info about whether the Y inputs work. The trace looks a bit dim but that's probably the camera, least it's showing one. Maybe you could get further assurance.If you're looking at Bio and EEG signals then I would have thought the ability to store and capture waveforms would be quite important, but I understand your issues. If I were you, I would be watching the EUR / US$ exchange rate like a hawk... you sound quite close.

author: nctnico
author_rank: Super Contributor
timestamp: December 27, 2016, 09:19:13 pm
content: When dealing with EEG signals I'd really get a DSO because analog oscilloscopes are very bad at dealing with low frequencies. Below 50Hz things just get really bad (useless).

author: alex.martinez
author_rank: Contributor
timestamp: December 27, 2016, 09:35:52 pm
content: Quote from: Gyro on December 27, 2016, 09:09:33 pmIndeed, I downloaded the manual and the specifications are included! I see it has an AC coupling low limit of 10 Hz, I think I might work around that, the finest filters I'm using have a 50 Hz low cut off. Has no math options, but after all I'm using an ADC as you may have guessed. However the CMRR is quite low. Well, I will give it a shot, I called the seller and asked if I can test his scope and agreed on that, I will just bring one of the sensors with the filters and test how the signals appears.One thing I don't find any information on is what's Vernier's Vertical Sensitivity, any clue on what is it?Thank you very much!

author: Gyro
author_rank: Super Contributor
timestamp: December 27, 2016, 09:48:18 pm
content: The AC coupling low limit is just set by the internal coupling capacitor and the 1M input resistance - to get lower you would simply select DC mode and use a bigger external capacitor. At those fregencies though, you're mostly just going to see the flicker of the dot scanning.The Vernier Sensitivity is simply the adjustment range of the little fine adjust knob on the front of the main input sensitivity switches (13) on the front panel diagram.It's good that you can at least visit with one of your sensors and have a proper look - It would be sad to follow up one mistake with another one.

author: alex.martinez
author_rank: Contributor
timestamp: December 27, 2016, 09:59:17 pm
content: Quote from: Gyro on December 27, 2016, 09:48:18 pmThank you very much for your help! I hope to understand oscilloscopes one day as you do. Time to time, as we say in spanish.

author: Gyro
author_rank: Super Contributor
timestamp: December 27, 2016, 10:04:08 pm
content: Do please let us know how you get on. It's always nice to hear.

author: Fungus
author_rank: Super Contributor
timestamp: December 27, 2016, 11:10:52 pm
content: Quote from: alex.martinez on December 27, 2016, 06:01:22 pm40 or 50 Euros, max.But...I think it's unsuitable for what you're doing. For "biosignals" it's very usefult to be able to connect it to a PC. An old analog 'scope simply won't do that.Quote from: alex.martinez on December 27, 2016, 06:01:22 pmFor 100 Euros you could also get a basic Picoscope which has better software (I'm assured)https://www.picotech.com/oscilloscope/2000/picoscope-2000-overviewEdit: No you can't. The cheapest one is 139.

author: alex.martinez
author_rank: Contributor
timestamp: December 28, 2016, 02:42:43 pm
content: Quote from: Fungus on December 27, 2016, 11:10:52 pmI know that it won't serve that purpose, I just need to get the feeling of what is happening between stages in the sensor, filters and amplifiers. I use a 16 bit ADC and I do all my math on python. Moreover, I'm just a Engineering student who happened to specialize in a very specific field of electronics, I feel that I could gain a lot of knowledge using this basic scope, I want to explore oscillators in depth, try to test my own built electronics. As I said, I will focus on a proper 600 bucks DSO in the future as for now I cannot justify the expense.Another point is that Spain is not a country with an engineering tradition, the devices on the second hand market are scarce and the few cheap ones are old. It happens that I contacted some of the particular sellers and they did not even know what the scope was for, mainly stuff they found in their father's garage and want to get some money for it. You can argue with them about how overpriced it is, but they won't ease the price, because they see other scopes in the market with that price. The only ones I found suitable are those I mentioned earlier, a single probe that is sold in the US for 5 $ can cost up to 20 €. I've been looking for some old school Tektronix stuff, but all of them are for 150 € or higher, and located on the Peninsula.I also checked the PicoScope you showed me, very decent, but if you want to ship it o Europe it includes a 20 % import tax. So the price scales up to nearly 200 €.For now, I will check those scopes I mentioned, I have a pocket signal generator that emulates brainwaves for my sensors calibration and I will see if it serves any purpose.Thank you for your response!

author: Fungus
author_rank: Super Contributor
timestamp: December 28, 2016, 03:22:46 pm
content: Quote from: alex.martinez on December 28, 2016, 02:42:43 pmSo long as you're clear about that then go ahead. At the end of the day you spent less than 100 Euros.Quote from: alex.martinez on December 28, 2016, 02:42:43 pmTell me about it.(And I live in a big city (Valencia). In Canarias it will be ten times worse).

author: harveyradar
author_rank: Contributor
timestamp: December 29, 2016, 04:45:02 am
content: Goodwill GOS 622 Analog Oscilloscope schematic is found athttp://elektrotanya.com/goodwill_gos_600g_60mhz.pdf/download.htmlregardsharvey

author: alex.martinez
author_rank: Contributor
timestamp: December 29, 2016, 05:33:51 pm
content: Quote from: Gyro on December 27, 2016, 10:04:08 pmWell, I came from the guys home. The oscilloscope is nearly new, he bought it first hand from the vendor, and used it only 2 times. It is in a perfect condition, not even a single scratch or stain! It's basic and I tested it with the waveform generator. The signal at 100 Hz is pretty damn acceptable in the screen (if I want to include any picture in my TFG I will use long long exposure and I will edit the colour curves at low frequencies). I got the manual both in english and spanish (if anyone wants the spanish version I will scan it and upload it, very rare document), the seller even had the packaging with the original foams and silica bags! I finally bought it for 80 €, it will serve well my purpose, I hope I can learn a lot with it, you will definetly hear from me and my Op-Amp adventures in the Beginners forum after my exams haha.I attach some of the pictures I've taken with my phone.Quote from: harveyradar on December 29, 2016, 04:45:02 amThank you very much! I have dowloaded it and saved it in my drive, the seller actually found and gave me the manual.Thank you very much to all, amazing forum and kind people !

author: Gyro
author_rank: Super Contributor
timestamp: December 31, 2016, 07:11:01 pm
content: Glad it worked out so well for you. Thanks for reporting back!