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I'd like to repair older computers, such as C64's, Atari's, Apple IIe's etc and their power supplies. I have a multimeter already but I'd like to get an oscilloscope. I've been offered an Owon PDS5022S really cheap, would this be suitable to start with?

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    \$\begingroup\$ If you are just starting out, anything is good to start with, if only to learn how to use them, and to discover what you really need. \$\endgroup\$ – gbarry Sep 22 '12 at 2:45
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    \$\begingroup\$ True, but I'd like to know I'm on the right track at least. In particular, if the bandwidth would be suitable for that kind of work. \$\endgroup\$ – TheWombat Sep 22 '12 at 2:52
  • \$\begingroup\$ EEVBlog has several videos that cover entry-level oscilloscope selection: youtube.com/watch?v=JTG6jWL0ZqA, and youtube.com/watch?v=R_PbjbRaO2E for example. \$\endgroup\$ – JYelton Jul 24 '13 at 4:51
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Yes, the Owon should do okay for all the mentioned computers. 20MHz bandwidth is a perfectly good choice for your first scope, and will cover most of the "less complex" and older digital electronic components, for example small microcontrollers (e.g. PIC10, 12, 16, and 18F and similar Atmel, TI, etc offerings)

The highest clock speed out of the computers mentioned would be probably the Ataris - you don't specify which one but for example the Atari ST used a motorola running at 8MHz, and a later model used a 16MHz processor.
The C64 and Apple IIe used ~1MHz clock speed, so obviously they are no problem.

Note that most of the signals you will be looking at will be much slower than the clock speed, so even if the clock speed is above your scope bandwidth it doesn't necessarily mean you cannot use it. It just gives a very rough guide, as you know (almost) for sure all the signals will be slower than the main clock speed (barring things like wireless peripherals or video ICs that may generate their own high speed clocks)

Another thing thing to note is although the bandwidth is given as 20MHz, the sample rate is only 100Msps (mega samples per second), so a 20MHz square wave will not look very square at all (as you will only get 5 samples to recreate one cycle of the waveform).
Usually decent scopes are specified with a bandwidth of around a 10th of the sample rate, so over 10MHz this Owon will not be ideal. Looks like they were pushing the specs a bit to make it sound a better.
However, they are pretty good scopes for the price - I have a 200MHz later SDS model which samples at 2GHz, so it looks like they may have reconsidered about the sample rate vs bandwidth specs.

Out of interest, how much will you be paying (just to make sure it's a reasonable price)

EDIT - $150 (I assume USD) sounds pretty reasonable for a new DSO of this spec. Here are a few interesting alternatives:

TEKTRONIX 2235A 100MHZ OSCILLOSCOPE - $175 (analogue scope) USED - you can get plenty of higher bandwidth analogue scopes for the same price. The downside with an analogue scope is you cannot save the waveform, or see before the trigger (pre-trigger) or do FFTs/waveform arithmetic. Still very usable though - even though I have a good DSO I still use my analogue scopes regularly.

Tektronix TDS 1002 Two Channel Digital Storage Oscilloscope 60 MHz 1 GS/s LCD Bid currently at $172 (USED) - probably go for double this but definitely worth watching, a nice scope.

HP 54542A Oscilloscope 500MHz / 2GS/s , 4-Channel - Just for interest, be nice if it went cheap...

Siglent SDS1062C Digital Oscilloscope 1Gsps/60MHZ DS1052E - £189 (GBP) NEW - There are quite a few scopes around this price up to 1Gsps/100MHz or so, which is four times the bandwidth of the Owon PDS5022S. In case you want to spend a bit more.

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  • \$\begingroup\$ I can get the Owon for around $150 \$\endgroup\$ – TheWombat Sep 22 '12 at 3:39
  • \$\begingroup\$ That sounds like a decent price, I'd probably go for it. I added a few different types of option (used, new, digital analogue) just so you can get an idea of what else is out there. For $150 new you will not get better than the Owon, but you can get some pretty good used stuff (make sure it's working and there is a return option though if you go this route) My first couple of scopes were analogue Tektronix like the first option, and they are both still working fine after lots of use - Tek make very solid analogue scopes, mine are both over 20 years old. \$\endgroup\$ – Oli Glaser Sep 22 '12 at 6:10
  • \$\begingroup\$ @Oli Glaser Sorry for the off-topic, but did you mention you had problems with fan on your scope? If that was you, how did it turn out in the end? \$\endgroup\$ – AndrejaKo Sep 22 '12 at 9:57
  • \$\begingroup\$ @OliGlaser in your opinion, what brand is best to go with? Reliability, most solid basic feature set, etc. \$\endgroup\$ – Toby Lawrence Sep 22 '12 at 12:23
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    \$\begingroup\$ @TobyLawrence - I think picking one brand is not possible, since they all make good/bad models. For reliability/support/quality the big names like Tektronix, Agilent, Lecroy are the ones you would probably always choose if money is no object. For the price/specs the "lower end" names like Rigol/Owon/Atten/Sigilent are almost always going to give you better raw bandwidth (and likely buffer memory) for the money. If you look at e.g. the latest Tek offerings for ~£500 you only get 2.5k samples buffer memory and 50MHz BW. \$\endgroup\$ – Oli Glaser Sep 22 '12 at 22:48
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Regarding the general characteristics of the oscilloscope I think it should be good for analog signals.

One thing I've noticed about the Owon PDS5022S is the low memory per channel. If you are working with digital signals, specially serial data you will find that 5K per channel is useless. In my opinion, for digital signals, memory length is one of the most important things to pay attention.

I own a Rigol DS1052D that have 512K per channel and sometimes I feel the need for a little more.

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I would personally save the $150 and put it towards a reasonable-quality digital storage oscilloscope.

I started my career with analog gear, then one sunny day I got my mitts on a Philips Combiscope. Analog mode, meh, just like any other scope. Digital mode, hmmm... and "aaaaaaa" went the angelic choir as my eyes were opened widely.

Silly anecdote aside, there are many advantages brought to the table by DSOs over analog scopes:

  • waveform capture and retrieval to a PC
  • communication protocol decoding
  • mathematical functions on waveforms (including FFT for pseudo-spectrum analysis)
  • deep-zoom memory (acquire lots of samples and zoom in on important parts)
  • waveform measurements (peak, average, RMS, etc.)
  • easy automation via GPIB/USB/RS232/Ethernet

There are some limitations in terms of resolution (most DSOs have 8-bit vertical resolution) but trust me, once you go digital you may never want to go back.

I currently use an Agilent DSO5014 for my daily work (8 MB memory and I2C / SPI decoding enabled) and I absolutely love it. This isn't a cheap scope, but lower-end DSOs offer many of the features of the fancier ones. I would seriously consider a used HP / Agilent / Tektronix, or even go for a new Rigol scope.

Go for 100MHz bandwidth at minimum. You can always turn on 20MHz BWL when needed, and the bandwidth is needed when dealing with fast analog stuff (switching MOSFETs and diodes) and high-speed digital. Since you're wanting to work on power supplies, 20MHz is too slow in my opinion.

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Lower speed, but free, Google "oscilloscope computer sound card".

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    \$\begingroup\$ It's always nice to see activity from recent members, but do keep in mind that in general we like a bit more elaborate answers here. \$\endgroup\$ – AndrejaKo Sep 22 '12 at 10:09
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    \$\begingroup\$ @AndrejaKo I know that's what the group seems to want, but I prefer short and to the point as this answer is. \$\endgroup\$ – kenny Sep 22 '12 at 14:33

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