T-Beam V1.0 measuring only 1.8V on the 3.3V pin

T-Beam V1.0 measuring only 1.8V on the 3.3V pin

I have two T-Beams, a V0.7 and a V1.0.
Got the V1.0 recently and haven’t used it much yet.

I have 0.96" OLED displays connected to both T-Beams and the display on the V1.0 is much dimmer. Switching the displays made no difference. Whatever the display, the one on the V1.0 is always much dimmer.

The displays are connected to GPIO 21, 22 and the GND and 3.3V pins next to GPIO 22.
When measuring the 3.3V pins of the V1.0 board it shows only 1.8V. Removing the display makes no difference. Whether battery or USB powered makes no difference.
The 3.3V pin on the V0.7 board correctly measures 3.3V.

On the V1.0 I have enabled all peripherals with the code shown here:
TTGO T-Beam - #179 by jezd

  • Does measuring only 1.8V on the 3.3V pin sound familiar?
  • Can the 1.8V on the 3.3V pin be caused by the power management chip?
  • Can this be fixed with code/configuration?
Pin Voltage on T-Beam V0.7 Voltage on T-Beam V1.0
5V (USB powered) 5.0V 4.9V
5V (battery powered) 5.0 4.0V
3.3V 3.3V 1.8V
LoRa supply 3.3V 3.3V (normal!)
Ublox Neo-M8N supply 3.3V
Ublox Neo-6M supply 2.75V

Voltage of Li-ion battery in each T-Beam is around 4.0V.

Is this a buggy T-Beam V1.0 with malfunctioning power management chip?

Is there any kind of schematic for the power supply on that?

Does the power consumption with as little as possible on rule out some sort of short?

Are you measuring with a meter that would see an average, or something that could see toggling, like a scope?

It’s not clear to me what you mean here.

Measured with a multimeter.
I have not yet checked with a scope but will be good to try for more information.
(I have only one V1.0 so can’t compare any measurements.)

If the voltage is too low due to some electrical fault, that might cause excessive current draw overall; eg if you have two shorted adjacent MCU pins one high and one low which have wrestled each other to a tie, you’ll probably see power wasted. This is probably from a regulator or PMIC not an MCU gpio, but still the principle of faults often showing as excessive power may still apply.

I take it they don’t publish a schematic?

Just power up of AXP192 outputs (as in example you are referencing onto) could be not sufficient :

axp.setPowerOutPut(AXP192_LDO2, AXP202_ON);
axp.setPowerOutPut(AXP192_LDO3, AXP202_ON);
axp.setPowerOutPut(AXP192_DCDC2, AXP202_ON);
axp.setPowerOutPut(AXP192_EXTEN, AXP202_ON);
axp.setPowerOutPut(AXP192_DCDC1, AXP202_ON);

it is worth to make explicit 3.3V setting for DCDC1:


You may use this as a reference

I take it they don’t publish a schematic?

1 Like

Thanks all. Will give it a try soon as I have time.

Will be great if axp.setDCDC1Voltage(3300) can fix my issue.

That fixed it! :+1:

When a pin is labeled 3.3V one expects it to be just that, without first having to setup the power management chip.

Luckily the issue can be fixed in software and is not caused by faulty hardware.