| Reference | Typical Value | Function | Failure Indicator | | :--- | :--- | :--- | :--- | | | 2A – 5A 250V | Protection | Open circuit (no continuity) | | RT1 | 5D-11 | Inrush limit | Cracked, high resistance (>50Ω) | | C1 | 100µF/400V | Bulk storage | Bulging top, low capacitance | | Rstart | 150k-300k | Startup | Open circuit (no P_IC VCC) | | Q1 | 600V N-MOSFET | Switching | Shorted G-D-S | | U1 | UC3844 | PWM control | No oscillation on pin 6 (Gate) | | U2 | PC817 | Feedback | Low CTR (output can’t pull low) | | D5, D6 | UF4007 | Rectification | Shorted or open | | U4 | 7815/7824 | Linear reg | Input voltage present, output zero |
: Often color-coded to distinguish fire-fighting water from domestic supply. Isolation Valves Yp-05 Schematic