This paper presents a detailed study of 4 eclipsing binary systems: TIC 142154041, TIC 1400824435, TIC 237278994, and TIC 140638648 using photometric data from the TESS space telescope. We classified the stars using a modern classification system based on the concepts of Roche lobes and Lagrange points. We computed and corrected their orbital periods and initial epochs through O – C diagram analysis. For better understanding of their variability, the phase curves and light curves are also presented in the article. No significant period variations were observed for TIC 142154041 and TIC 1400824435. We constructed an O – C diagram for TIC 237278994 and found quasi-periodic variability, with the primary and secondary extrema showing antiphase behavior. This pattern is consistent with the O’Connell effect. Using a Lomb-Scargle periodogram, we estimated a rough period of the O – C variability for each type of extrema and suggested that it may be related to star spots on the surface of one of the components. In addition, we identified cases of the O’Connell effect for TIC 140638648. For TIC 140638648 the primary and secondary minima (using Fourier decomposition) were found to be in antiphase, confirmed by the dominance of the second harmonic (0.0751 mag) over the first (0.021 mag) with a phase shift of δ₂ = 3.098 rad. These results show that O – C analysis of high quality photometry can reveal effects like the O’Connell variability and harmonic patterns that are hard to notice based only on the light curve; this gives new data and clues about how star spots and surface activity shape the light curve of eclipsing binary systems.