Buying a Used Oscilloscope – What Should I Test Beforehand? - Page 1
Forum section: electronics / testgear

author: LooksikR
author_rank: Newbie
timestamp: July 21, 2025, 07:33:17 am
content: Hey everyone, I'm planning to buy a used oscilloscope and want to make sure I test it properly before handing over any cash. I have a cheap DSO138 DIY oscilloscope that comes with a built-in square wave generator, would that be enough to check if the used scope is working correctly? Any tips on what else I should look out for during testing?

author: tautech
author_rank: Super Contributor
timestamp: July 21, 2025, 07:56:35 am
content: Quote from: LooksikR on July 21, 2025, 07:33:17 amWelcome to the forum.Your first sanity check foranyscope is the probe compensation output, usually 1 kHz @ 3-5V amplitude.Older CRO's didn't offer these atprecisefrequency/amplitude but good enough to check inputs and probes were operating correctly.What are you looking to buy ?

author: tunk
author_rank: Super Contributor
timestamp: July 21, 2025, 11:22:28 am
content: Budget, and what will you be using it for?Depending on your budget, you may be better off with a new Zoyi ZT-703S (~$75) or Zeeweii DSO3D12 (~$90).

author: Grandchuck
author_rank: Super Contributor
timestamp: July 21, 2025, 11:29:34 am
content: Careful physical inspection first. Then use your signal source and operate all the controls on the scope you are considering to see if they respond as expected.

author: Aldo22
author_rank: Super Contributor
timestamp: July 21, 2025, 01:07:32 pm
content: CRO or DSO?Which models come into consideration?Perhaps there are known problems with certain models that you could check.

author: Fungus
author_rank: Super Contributor
timestamp: July 21, 2025, 02:17:13 pm
content: Quote from: LooksikR on July 21, 2025, 07:33:17 amWhat 'scope is it? Hard to say what to test without knowing that.Quote from: LooksikR on July 21, 2025, 07:33:17 amYes, but the 'scope will have a test signal output on the front panel.Use that...

author: coromonadalix
author_rank: Super Contributor
timestamp: July 21, 2025, 05:16:24 pm
content: normally you ask to see a screenshot of all passed tests or failed ones or with error codes,and all the probes to the 1khz signal test .... at same time or one after the otherif not stay away, look away

author: Doctorandus_P
author_rank: Super Contributor
timestamp: July 22, 2025, 03:13:32 pm
content: Check if all buttons and switches on the front panel do at least something.Rotary encoders going bad on DSO's is a common fault.Put some test signals into the scope, and test over a wide range of frequencies and amplitudes.Connect both (or more) probes to the same signal, and see if they track over each other on the screen. If there is a deviation, either the input amplifier or one of the probes is bad.If the scope should have a (noisy) fan, but is quiet, check if the fan is blocked. If it's blocked on purpose (to sell a quiet scope). Punch the con man in the face and run away.

author: Eagcress88
author_rank: Contributor
timestamp: August 14, 2025, 07:34:20 am
content: Quote from: Doctorandus_P on July 22, 2025, 03:13:32 pmGood tips! I’d also suggest inspecting for burnt components or capacitor bulging before deeper troubleshooting, as it can save much time!

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: August 14, 2025, 12:51:43 pm
content: Once you have found a used scope that you like, you can search in the forum for the scope and see if there are any problems inherent to the scope that you should investigate. The advice about seeing if the scope works using the front cal square wave is a good start in evaluating used scope. Also you might wish to make sure the probes are correct in their capacitance rating for the scope. The capacitance should be stated on the scope near the BNC and on the the probes. Of course look for a scope that meets your expectations in bandwidth....do you want a scope capable of higher RF ...

author: Grey_Dawn_Breaking
author_rank: Newbie
timestamp: August 14, 2025, 02:16:44 pm
content: Has anyone mentioned this video?I've used it myself for testing o-scopes before buying.