Yesterday I was testing capacitors when my tester decided to die. Let’s see what went wrong.
It’s a cheap, chinesium transistor tester, model K120263BSJH. I modded it to use 2×18650 instead of 9V battery, but for troubleshooting I soldered it to my variable PSU. Why?
That’s why.
Something got shorted, because I refuse to believe that a 100mA 5V LDO can draw ~340mA. What’s more, the LED indicator was very faintly lit all the time.
That kind of power draw results in hot components. Usually, a thermal camera would be used for this, but since I don’t have one, I used the IPA method.
Exactly as predicted, 7550A-1, the LDO got hot enough to evaporate the IPA. Time to desolder it.
But there was a surprise. LDO wasn’t shorted. On the PCB resistance from 5V to GND was about 3 Ohms. Filtering capacitor got shorted? Nope, after desoldering it the short was still there.
Well, time for voltage injection.
I hooked up my PSU to output of that LDO, set the voltage to 5V and…
Copious amout of smoke came from the area of the ZIF socket. After closer inspection, the SVR5-04 seemed to be burnt.
A quick google later I found out that this component is a protection circuit and it’s not necessary for operation. I still would like to have protection on my tester, so I will try to get one later, but for now I need a working tester, so for now I just removed it.
After turning it on power draw was more reasonable.
As I mentioned previously, I’ll need to get the protection chip and resolder the batteries, but otherwise it’s working again. Now I can again know how terrible some of my Chinese caps are :).
Thanks for reading!