What to look for in a used Oscilloscope

[stl_jones@yahoo.com]

Quick question: I'm going to look at/buy an oscilloscope on craigslist tonight. What do I need to do to test that it is fully functional?

 

[Sceadwian]

You should never pick 'one night' to buy an item on Craigslist, watch the posts for weeks, or you could end up buying scrap, pretty much anything sold there is 'as is' so you have the word of the owner and any images they posts as to the actual condition. Testing it is simple, you plug it in and try to use it to measure signals that are supposed to be within it's range, if you get what you expect it's good, if you don't it's either broken or you don't know what you're doing =)

 

[RCinFLA]

If it has rotary switches, for scale setting, and timebase setting make sure they are not intermittant causing jumpy settings. Make sure any potentiometers are solid and not noisy, intermittant as they are rotated. Look for burn spots in the CRT phosphors.

Check calibration if you have a function generator or other means to calibrate it against.

If two channel scope make sure there are two good sets of probes.

 

[Sceadwian]

Okay my post in hindsight seems totally inadequate.

If you can go to the location to test the unit, bring an MP3 player and generate a sweeping frequency as high as you can record. It's only audio but it'll test the basics. Probes aren't too much of a problem as long as you're not going high frequency range, they can be bought inexpensively. But a scope with probes obviously takes that out of the equation.

You never mentioned what kind of scope you're looking for, purpose is very important. If you're gonna mow your lawn and you have 25 acres you don't want to buy a push mower =)

 

[ronv]

I'm with RCA. I've had some old ones and purchase some use ones (tektronix) and the only problems I have seen have been with the switches and pots. It's really aggravating to try to use one that doesn't switch well.
Most have a calibrate test point you can use for test.

 

[stl_jones@yahoo.com]

THanks for your input. I wound up buying a 20Mhz 1020Leader scope off craigslist for $125, and a sweet signal generator/variable powersupply/ breadboard combo for $20. Was this a decent price for the scope?

 

[Dean Huster]

Don't be terribly concerned with noisy pots in a Tektronix scope. With pots, the general rule is "lose it if you don't use it". A noisy vertical position or vertical variable gain pot will clean itself with use. Rip the offending pot throughout its range 20 or 30 times and it will usually work like new. Since we tend to use "Channel 1" most of the time, the "Channel 2" pots get noisy as does the delayed sweep trigger level control. Make it a habit of turning these lesser-used pots throughout their range at least once a week.