Hello,
While trying to fix an SMPS, I hear a ticking sound.
I've checked all capacitors, but none seem to be shorted.
I then suspected an issue with the flyback transformer which has 3 leads on the primary (used in a push-pull configuration ?) and one of them, which is always connected to GND has a resistance reading in the order of Mega ohms with any of the other 2 leads on the primary.
But I thought let's check the MOSFETs first::
The circuit also contains a PFC circuit, controlled by a UCC3818D (D stands for the SMD version), with no TI logo on it...
I removed the MOSFETs from the circuit and tested them one by one with a multimeter in diode mode.
After "charging" the gate with the red probe on G and the black probe on S, I moved the red multimeter probe to the Drain, D.
At that point, one of the MOSFETs maintains a voltage drop reading across D and S for only 3 seconds. Other MOSFETs maintain the voltage drop as long as the probes are still connected to the MOSFET's leads.
Is this a problem with the MOSFET ? Or is it completely normal ?
Do MOSFETs also produce a ticking sound when defective ?
Thank you in advance,
Roger
While trying to fix an SMPS, I hear a ticking sound.
I've checked all capacitors, but none seem to be shorted.
I then suspected an issue with the flyback transformer which has 3 leads on the primary (used in a push-pull configuration ?) and one of them, which is always connected to GND has a resistance reading in the order of Mega ohms with any of the other 2 leads on the primary.
But I thought let's check the MOSFETs first::
The circuit also contains a PFC circuit, controlled by a UCC3818D (D stands for the SMD version), with no TI logo on it...
I removed the MOSFETs from the circuit and tested them one by one with a multimeter in diode mode.
After "charging" the gate with the red probe on G and the black probe on S, I moved the red multimeter probe to the Drain, D.
At that point, one of the MOSFETs maintains a voltage drop reading across D and S for only 3 seconds. Other MOSFETs maintain the voltage drop as long as the probes are still connected to the MOSFET's leads.
Is this a problem with the MOSFET ? Or is it completely normal ?
Do MOSFETs also produce a ticking sound when defective ?
Thank you in advance,
Roger
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