Check what gets warm. (Besides the 3.3v regulator)
In theory, the 3.3v regulator can handle 500mA. The CPU needs ~50, the SD card might another 40, the OLED display should draw ~20mA and the LEDs should draw ~20mA each. That leaves the BT module, which I’m not sure how much it draws, but I would guess around 150mW.
500mA is quite a lot for a 2x2mm chip though, so it’s not recommended to use the full power. But your setup shouldn’t use more than ~300mW if everything is working well, which I think should be fine.
Also, the 3.3v regulator will become warmer when you give it a higher voltage, which might happen while charging.
Thanks! I’ll get back tomorrow
The board works for 15 seconds, and then gets into reboot loop.
It is hard to figure out what exactly gets warm. All small black chips got warm.
Would it make sense to use an external chip to step down from 4v to 3.3v instead of putting this on the board?
Heat spreads. Unless the 3.3v is just going nuts, only some chips should be getting warm, but it can be very difficult to tell for a small chip.
No?
If the question is: Can you provide 3.3v from outside the board to make it work, the question is a resounding maybe, since it depends on what is actually wrong. If the problem is inside one of the chips that use 3.3v, you’re probably just making it worse by providing more 3.3v power.
I wish I has FLIR camera. It is hard to distinguish what gets worm first.
Obviously the board gets damaged, could be the bluetooth or the oled display. I will probably disconnect the OLED display and the BT module and replace the board. Will only keep the switch LED buttons.
Btw, I used 1 resistor for both switch button LEDs, would that be an issue?
Using one resistor for two leds basically doesn’t work.
At best, the brightness will vary when one led is on and the other is off.
If the LEDs are different colors, then one will turn off when the other is on.
What size resistor did you use?
I used 100ohm resistor. Those are LEDS inside primary and aux switches. They are always on.
I’m trying to disconnect everything from the v3.3 pin and see how the board performs.
Same thing. Feels like the tiny chip right under the SD card heats up most, but I’m not 100% confident. The whole things is pretty warm.
Does it make difference which BATT- is used?
I think you mean Q7, right? (See the part map for details.)
most of the interesting chips are on the other side of the board though…
However, if Q7 is indeed heating up, that would mean that a significant amount of power is flowing through the board. Q7 is supposed to be able to handle 2A, which is way more than what the board needs.
Feels like the Q7, but I cant comment on the other side. It is not accessible.
I ended up switching the board to the last working one. Disconnected the OLED and BT. Kept the LEDs with the single 100ohms resistor. Will see how that works long term.
Do you want me to send you the board for forensic purposes?
No, it’s usually not worth it. Most of the time it’s nearly impossible to tell what actually happened afterwards. Sometimes boards are fixable if you can work out which component is bad, but that’s different.
Sure. Thanks for your help!