A20112 Power Supply Schematic -
Apply an external 12V (current-limited) to the output. Measure TL431 Ref pin – should be 2.5V. If not, check R12/R13. Then check optocoupler LED voltage (should be ~1.1V). If both are fine, the optocoupler transistor side on the primary may be open.
Share your findings in the comments below. And remember: the schematic doesn’t lie—but component tolerances do. Always verify, measure twice, and power up safely. Keywords used: a20112 power supply schematic, a20112 circuit diagram, flyback converter, PWM controller, TL431 feedback, switching power supply repair, UC3842 application, 12V power supply troubleshooting. a20112 power supply schematic
Check D5 (Schottky) for shorts. Measure resistance across output terminals – if very low (<10 ohms), the output capacitor may be shorted. Apply an external 12V (current-limited) to the output
Apply an external 12V (current-limited) to the output. Measure TL431 Ref pin – should be 2.5V. If not, check R12/R13. Then check optocoupler LED voltage (should be ~1.1V). If both are fine, the optocoupler transistor side on the primary may be open.
Share your findings in the comments below. And remember: the schematic doesn’t lie—but component tolerances do. Always verify, measure twice, and power up safely. Keywords used: a20112 power supply schematic, a20112 circuit diagram, flyback converter, PWM controller, TL431 feedback, switching power supply repair, UC3842 application, 12V power supply troubleshooting.
Check D5 (Schottky) for shorts. Measure resistance across output terminals – if very low (<10 ohms), the output capacitor may be shorted.