The tester read it as 9881 ohms. Sure enough, when is a 10K 5% resistor. Capacitors – ceramic disc, electrolytic, and surface mount all worked as well. The tester even provided ESR values. The real test would be a transistor. When you pull an old 2N2222 in a TO-18 metal can, and poppe it in the tester and you will see the thing work – it show the schematic symbol for an NPN transistor with Collector, Base, and Emitter connected to Pins 1,2,and 3 respectively. Flipping the pins around and re-testing work as well. The tester show hFe as 216, and forward voltage as 692 mV, both reasonable numbers for a 2N2222.
The tester work surprisingly well – Tester is able to correctly identify BJTs, FETs, even esoteric parts.
So what exactly is driving this little tester? There are about 20 versions of it on the market, all of them from China.91 make is a seller on taobao.com, often referred to as “China’s ebay.” 91make’s front page features no less than 7 versions of the transistor tester, with various cases and LCDs. The Subversion repository for the project shows it is quite active, with the most recent check-in only a few hours ago. The project is also well documented. The English PDF is 103 pages, explaining theory of operation, the circuit itself, and the software. The document even explains some of the shortcomings of the Chinese versions of the tester, including using a zener diode where the original schematic calls for a precision 2.5V reference.
The devs also don’t officially support the clones, considering the quality and changes in design each manufacturer is baking in to their own version. There is a huge thead on the EEVblog Forum covering these testers. Some can be modified to be closer to the official version. In fact, with an ISP tool the intrepid hacker can update the firmware to the current rev from [Karl-Heinz’s] repository.
So the final verdict on this tester is that it is a thumbs up with a small caveat. These testers are built down to a cost (and that cost is as close to zero as possible). They’re great for sorting parts, but they’re no substitute for a higher quality measuring device.