3V3 output and current draw on SWITCH OLED

[retronexus]

Hi all,

I have an issue with a Switch OLED I am trying to fix up. Currently only injecting 4.2V/1A at the charging coil to test the soft boot stage and voltages.
The cap at the top right has the correct 4.2V on the input, while the output only shows 0.8V instead of 3V3 I have expected.

On top, just by connecting the PSU to the device with 4.2V/1A and no further action, I see a current draw of 0.62A. I would have expected 0.001-0.005A.

As a next debugging step, I injected 1V at the 3V3 output of the cap to measure the current draw, which would hint towards an IC drawing down the voltage. Though the amperage was significantly below 0.1A, which would exclude an issue on the 3V3 rail itself.

Could it be the 3V3 regulator itself then?

I would need some help how you would troubleshoot this

Thanks

 

[jkyoho]

did you put 10k resistor on battery thermal pin?

 

[retronexus]

did you put 10k resistor on battery thermal pin?

Nope, at this point I didn't fully boot up the device, so I didn't put the resistor in place. Would that be needed in any case to work?

 

[jkyoho]

Nope, at this point I didn't fully boot up the device, so I didn't put the resistor in place. Would that be needed in any case to work?

device wont boot without the 10k bypass resistor on the 3rd battery connector pin when you trying to simulate battery plug-in with Bench DC supply injecting 4.2v into 2R2 charge coil. Without 10k bypass resistor, switch wont turn on or go black after 1st logo( from my bad memory)

 

[retronexus]

Ah interesting, I thought it would not be needed for the first boot stage. I will try and see if this changes anything, Though I think the issue might be with the Voltage Regulator, given the injection of 1V directly into the output of 3V3 Cap shows no significant current draw downstream.

 

[retronexus]

It became even more strange now. I changed the 3V3 IC, with no change. The board still draws 600mA at 4.2V /1A injection before boot.

Then I removed for testing the MT92 and BQ chip, and still there is current draw of around 550mA. I am not sure anymore what to look for at this point?