Need help identifying SOT23-6 with marking code B984 (boost circuit controller)

ro0ter

Joined Jul 9, 2013
14
Photos attached.

This is part of the case circuitry of a bluetooth earphone set.
Unfortunately the case no longer charges the earpieces, see video: https://www.mediafire.com/folder/n4nfj3j2qpdyg/pamu+not+charging+case

The main part I am interested in is the B98̅4 (tried to put the combing overline only over 8, aint working that good):

I managed to find many many sot23-6 components (boost / step-up converters suitable for battery operation - e.g. very low quiescent current) but unfortunately none matches the pinout on the board...

I would also be interested to find the other parts on the board, it seems that there is no more led display of the case battery, although it does charge its 902030 (size) lithium battery when I connect the microusb. The led display is surely controlled by the (ST Micro) STC 15w404as cpu which might also be dead (but I dont really care about it).

The 57b4 might be some version of tp4057 but Im not sure what the YJ32 SOT23-5 is....

I had attached pictures with the entire circuit and closeups with all the parts in detail.

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pmd34

Joined Feb 22, 2014
520
Hi ro0ter, you could probably at least fault find the part of the circuit with the B984 on it, check for example if there is voltage across the 2 big capacitors which would be input and output. See if there are pulses on one of the terminals of the inductor.

ro0ter

Joined Jul 9, 2013
14
Hello pmd34,

Indeed, there is 5v across the output cap (and on the pogo pins touching the earpieces), but it cant hold the 5V when theres a consumer (e.g. under 100mA - what both earphones need). It cant even hold the 5V for one charging earpiece (requires 44mA).

Cleaned the earpiece contacts with isopropyl (although there are no debris, no oxidation process)... Charging the earpieces outside of the case (dont ask me how I did it...) will work, they will charge from whatever charge level to 100% in a couple of hours, eating max 44mA and 20mA towards the end of the charge cycle.

The boost controller is clearly the culrpit.

Heres a better view of the circuit boards front:

And heres a gif I just made (almos nailed it.. yet the vias are a little far.. no camera lens distortion correction, don`t know how to do that in gimp):

Hi ro0ter, you could probably at least fault find the part of the circuit with the B984 on it, check for example if there is voltage across the 2 big capacitors which would be input and output. See if there are pulses on one of the terminals of the inductor.

pmd34

Joined Feb 22, 2014
520
Hmm... the package marking is very elusive! Whether you can reverse engineer it and replace it with something similar..
See what frequency it is, check the feedback voltage (pin 3 by the looks of it)...

pmd34

Joined Feb 22, 2014
520
I would start by rigging in an external DC-DC regulator board first, a cheap one from ebay or amazon etc. and just make sure that it does solve the problem first.