1. 6N135M Substitution Conclusion The 6N135M aligns with the original part in key isolation specifications (5000 Vrms, single channel, transistor output with base pin) and output current (8 mA), making substitution feasible under certain conditions. However, several critical differences must be noted: its package width (10.16 mm) is larger than the original (7.62 mm), which may introduce mechanical compatibility issues; its current transfer ratio (CTR) range is relatively broad (7%–50%), while the original part does not specify CTR—actual signal transfer efficiency in the circuit should be verified; its maximum input forward current (25 mA) is higher than the original (12 mA), offering more margin on the drive side, but the input circuit must be checked to avoid excessive current limiting. Additionally, if the original circuit is timing‑sensitive, the switching times (typically 90 ns/800 ns) should be evaluated for dynamic performance matching. In summary, substitution is acceptable provided the mechanical footprint is compatible and the CTR meets the circuit’s minimum requirement, but bench validation of signal integrity is recommended.