188362 Schematic ⚡ Proven
To speed up your future repairs, compile the following data table based on your specific board revision:
| Test Point | Expected Voltage | Waveform | Common Failure |
|------------|----------------|----------|----------------|
| AC Input (L-N) | 110/230 VAC | Sine wave | Blown fuse, MOV shorted |
| Main Bulk Cap (+) | 170V / 325V DC | Ripple <15V | Open capacitor, bad bridge |
| PWM IC VCC (pin 7) | 12-15V DC | Stable | Startup resistor open |
| PWM Output (pin 6) | 0-12V pulsed | Square wave @ 50-100kHz | Dead IC, shorted MOSFET |
| Secondary +12V | 12V ±5% | Ripple <50mV | Bad Schottky, bad cap |
| Optocoupler LED (Anode) | 1.1-1.4V DC | Steady | Open TL431 or divider | 188362 schematic
Symptoms: Fuse is black, and you measure 0Ω between drain and source of the main MOSFET. To speed up your future repairs, compile the
Fix: Replace the MOSFET and the PWM IC. The IC often dies when the MOSFET fails. Also check the current sense resistor (typically 0.22Ω to 0.47Ω) between the MOSFET source and ground – if open, the IC will see no current feedback and may destroy the new MOSFET. Also check the current sense resistor (typically 0
Trace from the output (+5V or +12V) through the resistor divider to the TL431 cathode. The cathode drives the optocoupler LED. Then follow the optocoupler output back to the PWM IC.
To speed up your future repairs, compile the following data table based on your specific board revision:
| Test Point | Expected Voltage | Waveform | Common Failure |
|------------|----------------|----------|----------------|
| AC Input (L-N) | 110/230 VAC | Sine wave | Blown fuse, MOV shorted |
| Main Bulk Cap (+) | 170V / 325V DC | Ripple <15V | Open capacitor, bad bridge |
| PWM IC VCC (pin 7) | 12-15V DC | Stable | Startup resistor open |
| PWM Output (pin 6) | 0-12V pulsed | Square wave @ 50-100kHz | Dead IC, shorted MOSFET |
| Secondary +12V | 12V ±5% | Ripple <50mV | Bad Schottky, bad cap |
| Optocoupler LED (Anode) | 1.1-1.4V DC | Steady | Open TL431 or divider |
Symptoms: Fuse is black, and you measure 0Ω between drain and source of the main MOSFET.
Fix: Replace the MOSFET and the PWM IC. The IC often dies when the MOSFET fails. Also check the current sense resistor (typically 0.22Ω to 0.47Ω) between the MOSFET source and ground – if open, the IC will see no current feedback and may destroy the new MOSFET.
Trace from the output (+5V or +12V) through the resistor divider to the TL431 cathode. The cathode drives the optocoupler LED. Then follow the optocoupler output back to the PWM IC.
