While an invaluable tool, the Blue Ring Tester does have a few blind spots to keep in mind:
If you work with power supplies, CRT monitors, or motor drives, you know that a "shorted turn" in a transformer or inductor is a technician's nightmare. A standard multimeter will show perfect continuity, but the component will fail under load.
In a healthy coil, the energy rings down slowly over several cycles (high Q). If a short exists, it acts as a heavy load, absorbing the energy and causing the ringing to collapse immediately (low Q). Core Blocks of the Schematic Diagram blue ring tester schematic diagram exclusive
I’ve reverse-engineered and enhanced this schematic from a rare 1990s German repair manual. Build it on perfboard in 20 minutes. Test a known good inductor. Then test a dead CFL ballast transformer.
: Because it operates at low voltage, it cannot detect insulation breakdowns that only occur under high-power operating conditions. Transformer Testing with a Ring Tester Part 1 While an invaluable tool, the Blue Ring Tester
Detects the ringing amplitude.
Here is the you have been searching for. While many generic diagrams exist online, this version includes modern component substitutions and corrections for common errors found in vintage copies. If a short exists, it acts as a
| Reference | Value/Type | Role | Exclusive Note | | :--- | :--- | :--- | :--- | | | NE555P or TLC555 | Timer (Pulse) | Use CMOS TLC555 for low power/better stability | | Q1 | IRFZ44N or 2N7000 | MOSFET Switch | IRFZ44N handles high current flybacks better | | D1 | 1N4148 (Fast) & 1N4007 | Signal diode / Protection | The exclusive trick: Use a UF4007 (Ultrafast) for accuracy | | LEDs | Red, Yellow, Green | Status Output | 5mm high-brightness | | R-Core | 10 Ohm – 100 Ohm | Current sense | Variable pot (47R) allows calibration | | C_Pulse | 0.1uF – 1uF Polyester | Tank capacitor | Must be low ESR; avoid ceramic |
The microcontroller or discrete logic counter reads the number of pulses generated by the LM393 and displays the health status via an 8-LED bar graph. Shorted turn or completely dead coil. 4–5 LEDs (Yellow): Marginal component or low-Q inductor.
: A late design revision changed resistor R7 to 510 ohms to increase sensitivity for low-impedance components like horizontal deflection coils.
: A momentary push-button switches a current pulse through a