Looked up the S814 series of cmos voltage regulators and there is a 3 pin type with SOT-89-3 case same as yours BUT....... without the suffix numbers there is little chance of finding the correct one.
They range in output from 2v up to 6v.
pdf link below.....
Appear to be low dropout regulator meaning the difference between the input and the output can be small and the regulator will still operate whereas standard regulators will cease with around 2v difference.
Measuring the input voltage may show an indication of voltage required.
Noticed the 2 electrolytic caps close by originally and voltage markings on them will be above the regulated level so not much help there.
The quad chip operates over a range of 3 to 36v so that's no help either.
Only possibility would be original thoughts with the microcontroller operating voltage of 5v.
That would be about the limit of any help from a distance I'm afraid.
https://digchip.com/datasheets/parts/datasheet/432/S-814-pdf.php