Falla
Placa de control bloqueada / sin PWM
Tracks alimentado placas de control con blocked PWM salida due to shutdown, realimentación o protección paths.
What sin PWM actually means
No-PWM is different from no potencia. The control IC may be alimentado y still produce sin salida because a shutdown, VRD, thermal, overcurrent o realimentación path is holding it off. This is common in SG3525 y UC3846 soldadora placas de control.
shutdown lógica flow
Fuente auxiliar correcta
↓
PWM IC alimentado
↓
Referencia voltage OK
↓
Protection / VRD / realimentación signal comprobacióned
↓
shutdown inactive
↓
PWM salida appears
↓
Etapa driver habilitaciónd
Where to measure
| Comprobación | Normal / valor esperado | Significado si es anormal |
|---|---|---|
| PWM IC VCC | Stable | Auxiliary supply issue if low |
| Referencia pin | Stable reference | IC o supply falla |
| arranque suave node | Ramps normally | capacitor o clamp falla |
| shutdown/protect pin | Not active | Protection path is blocking PWM |
| salida pins | PWM forma de onda | Control IC disabled o damaged |
| Driver entrada | Waveform reaches driver | Broken trace o driver transistor falla |
Likely componente fallados
- PC817 optocoupler in protección o VRD path.
- S8050/S8550 small transistor holding shutdown active.
- sensado de corriente resistencia o peak-realimentación de corriente network.
- CA3140/LM324/LM358 realimentación comparador etapa.
- arranque suave capacitor, diodo o clamp component.
Repair principle
Never bypass a shutdown path permanently on customer equipment. It can be useful para falla aislamiento on the bench, but the final repair should restore the intended protección behavior.