caso de reparación
UC3846 shutdown Pin Active: sin PWM salida
Use this caso when a UC3846/KA3846 placa de control has supply voltage but the PWM drive is blocked because the shutdown o protección path is active.
Why the pin shutdown matters
On many placas de soldadoras inverter de control, the UC3846 shutdown path is tied to overcurrent, undervoltage, overtemperature, realimentación y arranque suave circuits. A máquina can look like it has a bad PWM chip even when an external protección branch is intentionally stopping it.
Comprobaciones to perform
| Comprobación | Valor esperado resultado | Si es anormal |
|---|---|---|
| UC3846 VCC | Stable control supply | Auxiliary supply o regulator falla |
| Referencia salida | Referencia present | Shorted reference load o damaged IC |
| Oscillator | Timing forma de onda present | Timing component o IC oscilador issue |
| pin shutdown | Not forced into shutdown during idle test | Protection transistor, optocoupler o comparador path active |
| salida pins | PWM appears when shutdown is released | Driver load, IC salida o downstream compuerta-drive issue |
Isolation lógica
Verify VCC y reference
↓
Measure pin shutdown state
↓
Trace protección transistor / comparador path
↓
Comprobación optocoupler y current-realimentación branch
↓
Release false clamp y retest PWM
Likely componente fallados
- Leakage o short in a small signal transistor connected to shutdown.
- Fallay optocoupler in realimentación o protección path.
- Salida del comparador stuck low/high depending on placa design.
- Open sensado de corriente resistencia path causing false protección.
- Bad solder joint around the UC3846 socket o driver connector.