Intermittent Power Down on Ignition and Rapid Beeps

I’m experiencing an intermittent but frequent issue with a saber I’m installing with proffie v3.9. When igniting the saber, it powers up, and then down again. It does this as if the switch had been pressed twice, not as if power was suddenly cut (happens both with switch and gesture ignition). Subsequent ignition attempts can sometimes be successful. One other symptom that I observed was the 5 rapid beeps that I understand indicate low battery. This will usually occur moments after powering down the saber. I’ve checked solder joints for anything loose that could be causing issues, but haven’t found anything.

For more build and config details, see the following link to another post where I’m working a different issue:

[Neopixel Blade Doesn’t Light Up](Neopixel Blade Doesn't Light Up

I found a post on this forum referencing a failure of a voltage regulator that would cause the 3.3V pad to read higher, but the pad on my board reads around 3V. As mentioned in the post linked above, the battery voltage I’m getting from the board via multimeter is around 4V.

I’m not sure what’s causing these two symptoms, but I suspect they’re related. Any insight would be much appreciated.

Could be cold solders, or a weak battery.
If you measure the voltage between BATT+ and BATT- on the board while turning on the saber, what do you see?
What does the serial monitor say?

I thought of cold solders, and the possibility of a weak battery. I redid any solder joints that looked even slightly questionable. The serial monitor reveals at least why the board is behaving the way it is. While a meter reads around 4V on the battery while the saber is both on and off, the serial monitor reads around 3V when the saber is off, and a drop to around 2.5V when it’s on. That would explain why it shuts down and emits the low battery beeping. Both of those readings would constitute low battery on a 3.7V 18650.

  1. Measure the voltage at BATT+ and BATT- on the board. Is it the same as the battery voltatage?
  2. Measure the 3.3v ↔ GND voltage, is it 3.3 volts?

The board is where I was measuring the battery voltage. Previously, I had also measured at the exposed leads, and it returned the same value as at the board, around 4V. The 3.3V pad, however, is now reading more like 3.6V with the meter.

That’s weird, and bad.
But it does explain why the battery readings are low.
Do you have warranty on this board? If so you might want to use it.

I talked to the Saber Bay where I bought it; and after a bit of a runaround, they said that I would have to talk to the manufacturer (TCSS in this case). I was hoping to avoid that, but it seems there’s no choice now. Both the speaker booster and the 3.3V pad regulator are bad. I gather that the former was easy enough to work around, but not the latter.

For my own curiosity, how does a malfunctioning regulator to an unused pad create the voltage drop on the board?

The code uses the input voltage to compare to, so if the input voltage is too high, then every other measured voltage will seem lower. Theoretically, this could be improved since the chip has a way to measure the input voltage against an internal voltage reference, but normally there is no need since the input voltage is always supposed to be 3.3 volts.