The transformer (labeled T101) had ambiguous pin markings on the draft. Using an LCR meter and ring tester, the primary inductance (1.2 mH), leakage inductance (32 µH), and turns ratio (primary:aux:secondary = 10:3:1) were measured. The verified pinout was added as a correction note.
| Symptom | Likely failure (from schematic) | Test point | |-----------------------------|-----------------------------------------------------|------------------------------------| | No output, fuse intact | Startup resistor open, or IC1 dead | Voltage at IC1 pin 7 (should rise) | | Output voltage jumps / unstable | TL431 divider resistors drifted, optocoupler weak | Output divider junction (~2.5V) | | Output low (e.g., 8V instead of 12V) | Secondary filter capacitor high ESR, or feedback loop broken | Check C2, C3 with ESR meter | | Squealing noise + no output | Transformer shorted turns, or output short circuit | Resistance across secondary winding | | Blows fuse immediately | Bridge rectifier shorted, MOSFET shorted D‑S, bulk capacitor shorted | Diode test on D1–D4, MOSFET | wannien 101v0 power supply schematic verified
3.3 V rail
power supply board. Finding a verified schematic is the first step toward a successful repair rather than a costly replacement. Understanding the Wannien 101V0 Board The transformer (labeled T101) had ambiguous pin markings
Three days of searching. Three days of wading through broken forum links, blurry images from Russian repair blogs, and a single, useless datasheet in Mandarin. He’d almost given up. Almost harvested it for parts. | Symptom | Likely failure (from schematic) |