Datasheet for the LM556, a dual timer that packs two 555-type timers into one package, as a 158 KB PDF. It describes pinout for both timers, supply range, trigger and threshold levels and typical astable and monostable circuits. Technicians use it to identify each section's trigger, threshold, discharge, reset and output pins, then check timing components and output waveforms with a scope. Compare the package and marking on the board with the document, since DIP and surface-mount versions share the same pin functions.
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