Cheap oscilloscopes on eBay

My oscilloscope was sick & shuts off after a few minutes. I checked eBay and found many scopes for less than $100 and some less than $50. Most of them don't have probes. That is probably why they are being sold. I guess people don't know they can buy probes for less than $10 and these are on sale for $3.95. https://www.mpja.com/40MHz-Oscilloscope-Probe/productinfo/15086+TE

So I got a working scope delivered for $68.00. I had 2 probes from my old scope but bought 2 of those because at that price, I can abuse them and not worry about it. They work just as well as my old probes.

The key about buying stuff on Ebay is to understand the reasons how come they are so cheap in the first place.

If those "gotchas" are known in advance, there will be less frustration, and actually satisfaction, later.

They said it works fine & guaranteed it But I did wonder how they knew it worked if they didn't have probes to test it.

When I worked in marinas, we had golf carts to get around. I noticed that a flat tire could be fatal for a golf cart. Instead of fixing the tire, they would grab another golf cart & put that one in the corner. People would consider it dead & start taking parts off as needed. That one would never run again.
That may be what is happening to these scopes.

I also hate it when my scopes tire goes flat. Right pain in the ass to change it

ClydeCrashKop said:

But I did wonder how they knew it worked if they didn't have probes to test it.

Click to expand...

You do not need probes in order to test/calibrate an oscilloscope.
There is nothing wrong with connecting a known signal (voltage/frequency) directly in to the Y inputs and seeing what comes up on the screen.
I am quite sure that this is what Tektronics et al do all the time.

Probes become useful/essential when the impedance (x pF capacitance) of the connecting cable and the input impedance (1MOhm resistance and 10 to 20pf capacitance) have a loading effect upon the circuit under test.

JimB

ClydeCrashKop said:

They said it works fine & guaranteed it But I did wonder how they knew it worked if they didn't have probes to test it.

When I worked in marinas, we had golf carts to get around. I noticed that a flat tire could be fatal for a golf cart. Instead of fixing the tire, they would grab another golf cart & put that one in the corner. People would consider it dead & start taking parts off as needed. That one would never run again.
That may be what is happening to these scopes.

Click to expand...

This is actually well researched by behavior scientists.

If I remember correctly, it is the broken window syndrome.

I always just assumed that the low prices for used scopes were simply due to availability more than the lack of probes. The market for used scopes is pretty well saturated with everything from basically new models to older analog scopes and everything in between. I don't know what kind of scope you got, but I suspect that the influx of relatively low-cost digital scopes with LCDs and USB scopes for hobbyists has helped drive down the prices on the more bulky CRT oscilloscopes in recent years. From there, dropping prices on older CRT DSOs has also driven down the price of analog scopes even further.

For my own part, I've always been just fine using the generic P6100-type 100MHz probes you can find on eBay. I was always under the impression that these were pretty common for many hobbyists to use. I never thought that low-cost passive probes were a secret or anything.

There are probes and then there are probes. I have a Tektronix 3.5Ghz active probe that retails used for about $1500 USD, several 4Ghz actives for about $250 used and some 500Mhz passives at around $80 used.
A sub $10 probe is exactly that. Don't expect a lot, a few Mhz capability.

I have probably too many old scopes about the place, I also have a cheapo usb one with cheapo probes, it does most jobs now and works ok.
Cheap probes are not so great at higher freq's, and watch out for cheap usb and handheld scopes, a lot are dc coupled only.

Perhaps in a decade or two, ALL analog scopes will become collectible items.

Right now, only analog Tek scopes enjoy that distinction.

I still use my 'fluke analogue scope, it outperforms all bu the best digi ones, cant remember what you call the tube now, but it'll respond to runt signals only nS long.