The case for buying a used oscilloscope

Not all test labs need oscilloscopes sporting 1 GHz bandwidths and multi-million-point digital waveform recording. When the needs lean more toward the basic side, used scopes can sometimes fit the bill and do so economically. Here are a few points to consider before ponying up for a used scope.

The go-to website for used equipment is, of course, eBay. But it may be worth checking local CraigsList sites if you happen to reside near a major tech hub. For example, when we checked the CraigsList site near Silicon Valley we found 17 legitimate listings for oscilloscopes. The average asking price was $260 but many listings were lumped around $100. However, scopes are likely to be more rare on CraigsList even in other U.S. tech hubs. Around Austin, Tex., for example, we only found eight scope listings. Around Huntsville, Ala. there were only three; around Raleigh, N.C., 14 scopes. You are likely to come up dry around less technically savvy locales. Around Cleveland, Ohio, we only found one scope listed within 50 miles.

The point of first trying local avenues such as Craigslist is two fold. First, it can save you the cost of shipping a scope from a more remote location. Shipping costs for scope listings we saw were sometimes in the $40-50 range, especially for older, heavier analog models. Second, scopes for sale that are close enough to drive to may allow you to inspect instruments billed as “working” to ensure they live up to their advertised condition.

When you can’t inspect a used scope in person, there are a few details to look for in the listing that may help assure the instrument actually functions. The key detail to look for is in the picture of the instrument: The scope should show a trace–that’s a good sign the instrument really does work. If you can also zoom in close enough to read the scope front-panel settings, they should correspond to the kind of trace you see on the scope screen.

Another bit of advice: It is easy to over-pay for old scopes. Psychologists say people often value goods they own higher than they would if they were to buy the same goods on the open market. That seems to also be true for oscilloscopes. To take just one example, consider a listing we found for a BK Precision 2120 20-MHz scope. The seller was asking $295 for this old two-channel analog scope. A little searching turned up the same model scope going for $120 from a different seller. Both instruments were advertised as being in working condition. Revealingly, a quick search on Amazon revealed 100 MHz two-channel digital scopes with a built-in signal generator and 1 GS/sec sampling going for $185. Which of these do you think is the better deal?

Advice we’ve seen recommends paying no more than about $50 for any working analog scope. A low-ball offer may get the seller angry at you, but clicking around on Amazon can reveal what your walk-away price should be.