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.

Measure voltage across C4 (VCC pin of PWM IC). It should rise to 12–18V. If it stays below 10V, replace C4 and check R5 (startup resistor). If still low, the PWM IC may be shorted. a20112 power supply schematic

Measure across C1. You should see ~300V DC (for 230V AC). If zero, check F1, MOV1, DB1. Check D5 (Schottky) for shorts

Introduction The A20112 power supply is a widely recognized model in the electronics repair and industrial maintenance community. Commonly found in LED display controllers, industrial automation equipment, and telecommunications hardware, this compact switching power supply unit (PSU) is valued for its reliability and moderate output capacity. However, like any electronic component, it can fail. When it does, having access to the A20112 power supply schematic is not just helpful—it is essential. It should rise to 12–18V

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.