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?
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.
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.
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.