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I purchased a used 20/100 MHz oscilloscope many years ago. It has always served me well to look at very simple sine and square waves for my hobby projects.

However, I have wanted to know if I got a 100% functional o-scope. Is there a way I can test or calibrate it to see if it is operating up to spec? I do not own a function generator.

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Well, the oscilloscope should have its own internal function generator for calibration purposes. Usually there will be two exposed pins on the front panel where the probe should be connected. It should be explained in the manual what type of waveform you should expect. This is also important for probe calibration too.

I don't know of any other easy way to calibrate it.

You could always mess with microcontrollers and try to generate some sort of calibration signal, but unless you have another oscilloscope to confirm that the device is producing correct signal, you can't be sure if the oscilloscope or the home made function generator or both are broken.

Another option would be to get it professionally calibrated, but that could be expensive.

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    \$\begingroup\$ O-scopes are not useful for high precision measurements. Maybe some of the high-dollar ones will do the job, but if you need a precision voltage measurement, use a voltmeter. If you need a precision frequency measurement, use a frequency counter, and so on. (Both of my digital scopes use 8-bit converters.) If your scope agrees with your voltmeter, and you see power-line frequency when your finger touches the probe, I'd consider it good enough. \$\endgroup\$
    – markrages
    Mar 4, 2011 at 19:49
  • \$\begingroup\$ Yeah, I don't use scopes for measurement, even at work. They're for looking at the wave, generally, not measuring it. \$\endgroup\$
    – endolith
    Mar 4, 2011 at 20:22
  • \$\begingroup\$ This clears up some things - I recently was testing an automotive ABS module where I should have expected an 11 volt square wave. The scope showed only a constant DC 8V whereas a voltmeter showed 11.9V. (As it turns out, the module was broken, no square wave at all was present.) But the voltage difference between the two measurement devices made me question the scope's accuracy. \$\endgroup\$
    – JYelton
    Mar 4, 2011 at 21:44
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    \$\begingroup\$ That's a pretty severe difference. I bet the module was in a high-impedance state, such that the impedance difference between the scope and voltmeter influenced the reading. If you measure low impedance, a battery or something, they should read about the same. \$\endgroup\$
    – markrages
    Mar 4, 2011 at 22:29
  • \$\begingroup\$ My scope has a rated DC gain accuracy of ±1.5% in the manual, and it cost $3,300 US new in '93. However, I've heard that a newer scope from Rhode+Schwartz may have a 14-bit ADC, and presumably with that kind of ADC they'd compliment it with high gain accuracy. However, if you have to ask the price - you can't afford it... \$\endgroup\$
    – Thomas O
    Mar 5, 2011 at 0:27

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