PDF datasheet for the SN7403N, a quad 2-input positive NAND gate with open-collector outputs, from the standard TTL 7400 family in plastic DIP form. Unlike the totem-pole 7400, its outputs need external pull-up resistors, an important detail when a line refuses to go high. The 15 KB document gives pinout, supply range and output ratings for bench diagnosis. Use it to identify gate inputs and outputs while probing, and confirm the device marking matches before substituting another part.
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