Chips on the back of the board:

STMicroelectronics 324 E9SU518 - Possibly an LM324 Quad Op Amp?

STMicroelectronics 339 E9W2513 - Possibly an LM339 Quad Comparator?

Unidentified Texas Instruments chip with the part number sanded off.

A2714 Power MOSFET

Large QFP chip with the part number sanded off and a red and a blue mark on top.

Interestingly, all the chips were covered in a clear coating that made it hard to read the part numbers.

It appears that whoever designed this board was trying to prevent reverse engineering by making it hard to read the part numbers on the chips.