4N29 datasheet in PDF, describing a photodarlington optocoupler in six-pin DIP that offers higher current transfer ratio than plain phototransistor types such as the 4N25. The document lists pinout, LED ratings, CTR, isolation voltage and the slower switching speed typical of Darlington outputs. Repair technicians use it to test isolation stages in supplies and interfaces and to choose replacements; avoid swapping a darlington part for a standard phototransistor without checking that drive and timing still suit the circuit.
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