The ringing signal is AC-coupled via C4 and clamped by D1, D2 to protect the comparator. The LM393 compares the ringing waveform to ground. For a healthy coil, the ringing crosses zero many times. The comparator outputs a series of pulses for each zero-crossing.
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The circuit is designed for high sensitivity and safety, operating at low voltages that allow for in-circuit testing without damaging sensitive semiconductors. Integrated Logic: The ringing signal is AC-coupled via C4 and
A Blue Ring Tester is an indispensable diagnostic tool for electronics technicians and hobbyists. It provides a quick, in-circuit check for high-Q inductive components like flyback transformers, deflection yokes, and switch-mode power supply (SMPS) transformers. The comparator outputs a series of pulses for
This avoids calibration and gives numeric results (e.g., “Rings = 12”).
Because inductors can produce high-voltage spikes (back EMF) when pulsed, the schematic includes clamping diodes. These protect the sensitive ICs from being fried by the very component they are trying to test. Component List for the Schematic
must be a low-loss, high-voltage component. Polypropylene (MKP) film capacitors rated for 630V or 1000V are ideal. Standard cheap ceramic discs will drift with temperature and yield false results.