I have two NanoVNAs here that both seem to have the same problem in that they very often don't power on.
The first NanoVNA is a white/gecko model (2 traces firmware, micro-USB, official ttrftech branded). It didn't come with a battery installed, so I ordered a 500mAh and soldered it to the + and - battery solder points on the pcb.
The second NanoVNA was purchased of eBay a couple of weeks ago (probably a clone) and is black with a USB-C connector and has no identifiable manufacturer's markings on it but it did come with a battery installed.
The batteries in both units have what seems to be a small integrated control circuit underneath some yellow kapton tape.
When I plug in a USB cable to charge the battery they just begin blinking the onboard LED slowly until the battery is full (and the blinking turns into a solid-on). I then unplug the USB cable and let the unit sit there for a few minutes until the LED turns off.
When I now move the switch into the ON position, nothing happens. This is the case for both models.
Here comes the weird part. When I briefly insert and unplug the USB cable so that the unit's LED comes solid-on for a while the unit DOES switch on. I can repeat this several times and it always works. The white/gecko NanoVNA doesn't even switch on when it's charging the battery.
The batteries in both units seem ok; I've tested them for an hour of continuous operation and they didn't run out of juice.
I've read some posts in this forum on installing a silicon diode for battery sensing, none of the units have this diode installed, but I don't think that matters. The firmware on both also doesn't show a battery indicator.
I'm a bit lost as to how to tackle this issue. The only thing I can think of is that maybe the integrated battery protection board causes a slight voltage drop that causes the on-board voltage regulator to trip up, but I have no substantial evidence for that.
Anyone else seen this behavior? Any idea as to what might be the cause and possible fix for this?
Marcel
VK2CEL
