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I bought a cheap china tablet and it worked fine for a few weeks. Yesterday while charging and using at the same time it got warm. I opened it and recharged the battery manually and it worked again. But it is not accepting any change through the USB port. Today I took a more closer look and found one IC was burned. The tablet is a BS109.

Is is possible to know what this chip could be? I'm guessing some voltage regulator, since voltage at battery +/- should be 4.x Volts and now only is 2.5 Volts. I see only a 4 then a burned hole and a 0 and a 3 (4?03). On row 2 I guess it is year and week. On another picture I think I see 4C03

Update. On a similar tablet I found that the chip is marked 4603

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    \$\begingroup\$ Guessing a pass FET or possibly a Vreg. \$\endgroup\$
    – TonyM
    Commented Aug 20, 2017 at 9:09
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    \$\begingroup\$ Partially reverse engineering a schematic usually helps \$\endgroup\$
    – PlasmaHH
    Commented Aug 20, 2017 at 9:13
  • \$\begingroup\$ Please provide a picture showing more of the area around that SOT-23-5 (it may help reverse engineering or proofing assumptions). Crop the existing image to the chip itself. \$\endgroup\$
    – try-catch-finally
    Commented Aug 20, 2017 at 9:14
  • \$\begingroup\$ I checked another tablet. The chip is marked 4603. I think it is a voltage regulator of some kind. If I measure voltage on the 2 pins on the left (on second picture), the lower is positive and the above is negative. Without USB power it gives 3.6 Volts. The three other pins give 0 Volts when only running on battery. If USB is plugged in, the 2 pins give 3.8V and the 3 pins below gives about 5V. \$\endgroup\$
    – Magnus
    Commented Aug 20, 2017 at 11:50
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    \$\begingroup\$ Search the obvious place for "SOT-23-5 4603" and you'll get a number of possibilities. At least two of them are buck converters, apparently with different pinouts, and another is a 2.5 ohm FET switch. You'll have to do some legwork and testing (e.g. which pins are connected to GND) to eliminate the wrong ones : hopefully you'll be left with one possibility, and hopefully that one will work. \$\endgroup\$
    – user16324
    Commented Aug 20, 2017 at 12:37

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After digging I found that it is probably a WS4603 from Will Semiconductors Ltd. This chip is hard to find. I will try and replace it with a SY6280AAC

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