Hello,
first thank you for sharing this project. I made a (mostly) through-hole version and when I first tested it, it seemed to work. I was getting the 100mV for a 1ohm resistor (after minor tweak of the pot), a then tried a few different caps that appeared to have somewhat reasonable vals. Before the first test I also double and triple checked that everything was correctly connected etc..
So after the test I removed the battery again and left the circuit untouched (in the same location where I tested) for a day, until I could buy a plastic box to put it in. I put it in the box, soldered the 1-pol switch and connectors for test leads to the prepared wires, the same wires to which I had clamped the test components and DMM earlier. Really nothing there that could've caused any kind of issues.
I then went ahead to try it, again with the 1ohm resistor, but now everything was dead. I wasn't getting any readings. After checking the circuit it turns out the 78L05 seems dead. It's getting the 9V in, but 0 comes out. So, first time it worked, I even measured the output during my first test, then without having done anything inbetween that in any way should be able to affect the functionality, the volt. reg. has died.
Now, I'm
very amateur. If some device, typically older, breaks down I usually check for bad caps. I figured this tool could help me with that. Otherwise my usual "constructions" are in the form of a microprocessor and a few surrounding components, so my skills to determine what could've gone wrong are limited. Googling what might cause the volt. reg. to fail, the only normal thing I could find was that they don't like reverse current/voltage and typically you're suggested to add one or two diodes to prevent this.
The ua78L05 datasheet (
http://www.ti.com/lit/ds/symlink/ua78l05.pdf) confirmed this, in section 8.2.2, and also mentions it can happen during startup. I'm not seeing this kind of protection in the ESR meter circuit, so I'm wondering is that reverse voltage situation not possible here? If not, does anyone have any idea what else could break the regulator? Could I add those diodes only and have everything else still working without changes?
Any hints would be greatly appreciated.
(I do have one regulator left, but it feels like simply replacing it doesn't fix the root cause and only risks breaking that as well. Then I'd have a problem because ordering new ones within forseeable future isn't in the books with the rediculous shipping costs around here.)