Part identification, or alternative part - 63 613 Power Management chip
Looking for ic markings starting with 63, the OB2263 and twins HT2263 and another duplicate seem a very good candidate.

The first datasheet shows Marking Information "63 YWW" which would be 2006, week 13.



My assumptions:


Gate pin is connected by 22 ohm resistor and anti-parallel diode to a
through-hole mosfet.
FB pin and GND pin are connected to through-hole optocoupler located below silkscreen text D4 (like TYPICAL APPLICATION in datasheet). Note C3 on the PCB is the capacitor close to the optocoupler in TYPICAL APPLICATION.
R5 and C1 form a RC filter connected to the SENSE pin
the through-hole component between silk R1 and R2 is an elco, and forms with R1 a filter for the power supply to the chip as in TYPICAL APPLICATION.