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Used oscilloscope considerations

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ABCD:
I see a lot of used scopes claiming they can't say if the unit is calibrated, or what the calibration status is.  If I buy one of these, I may not be able to tell if it is out of calibration or not, or can I?  Another question is with regards to probes.  Most don't come with probes, or power cords for that matter.  How generic are probes?  (I assume power cords are generic enough.)

I'm trying to sort through the many listings out there and those two things (no probes, unknown cal) stick out the most.

joelby:
Calibration's not always a huge problem, and you can always check if it's not *too* far out of spec using a voltage source and decent multimeter, and a signal generator or oscillator module.

Generic probes are usually okay for most things, but be careful if the oscilloscope has a 'smart' input that detects the type of probe. I have a DSO that doesn't allow the probe divider to be set through the menu, so without the manufacturer's probes or some fiddling/reverse engineering (sometimes it's a specific resistor value to the extra pin, and sometimes it's an I2C/SPI ROM), you're stuck at 1x. If there's a good photo of the probe input you'll be able to see if there are any extra pins around the BNC jack. If you can get a copy of the manual, you'll be able to see if there's a menu option!

vk6zgo:
Most Oscilloscopes use normal domestic type IEC cables---some very old types had special connectors.
People get very uptight about calibration with Oscilloscopes,but you very rarely need any great degree of accuracy.

You can do a good check on DC coupled voltage accuracy with an AA cell & a DMM.
Just measure the open circuit voltage of the cell,& compare it with the deflection on the screen,with the Oscilloscope on "auto".

1 cycle of 50Hz mains is 20 milliseconds ,or of 60Hz is 16.666 milliseconds.(don't cram your probe into the mains socket,you can pick up enough hum out of the air)

PAL  line sync pulses (& I think NTSC ,too),are 4.7uSecs wide.

If you don't have "Smart" probes,you will have to do the 10X calculation in your head,like everyone did in the old days--it isn't at all hard!

VK6ZGO

ABCD:
Thanks for the replies.  The scope in question is a 20MHz analog scope, going for around $50.  I guess I can't go too wrong with that.

Simon:

--- Quote from: vk6zgo on June 02, 2011, 02:21:29 am ---
1 cycle of 50Hz mains is 20 milliseconds ,or of 60Hz is 16.666 milliseconds.(don't cram your probe into the mains socket,you can pick up enough hum out of the air)


VK6ZGO

--- End quote ---

Had to chuckle at that

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