I got a Non-Linear Systems (NLS) MS-215 Miniscope for $20 at a hamfest. After removing the three D-sized lead-acid batteries and running it on 7.2vdc, it works great! Shown above is the output of my KX1 on 80m.
I've consulted with Paul NA5N and he said the battery is the main issue:
These batteries are usually the culprit. The power supply takes 12-18v from a wallwart (the DC barrel connector), which drives an internal switching power supply. The internal batteries are part of the filtering network. When these batteries go bad, they become a short circuit, which becomes a short across the internal power supply. Simply disconnect the spade lugs (black and red wires) from the battery and tape up to keep from shorting against something else.
I've also read that the CMOS 4066 switches (socketd) are sometimes bad.
I don't have an MS-215 manual but here's an MS-230 manual (from BAMA): MS-230 manual
Here is more information from Tom W0EAJ:
The xfmr feeding the miniscope is only 9 VAC.
The scope does not have a switching power supply (except the flip-flop for the HV); it merely contains a regulator / charging circuit for the (3) 2v 2ah lead-acid batteries, formerly made by GATES (p/n 0810-0004), but now sold by Battery Mart for about $9.00 each.
Although the scope will run on 7.2v, it is not recommended per NLS, which is still in business. They no longer make the scope (can't get the CRTs anymore), but did up to about 2005.
Most frequent problem with them is dirty slide and toggle switches, and dirty pots. An application of DeOxIT (caig labs) will fix all of that.
www.batterymart.com (enter the original Gates p/n and it'll show you the one you want)