Hi Guys,
I have another unit that's beating me up here.
This set starts up and is in standby mode. Upon pressing the power button the set makes a relay clicking sound and then the on board "piezo speaker" which sounds when pressing any of the on board buttons starts making a long beeping sound. In the mean time the secondary voltages (those that should start up when pressing the power button) do not come up.
This is my findings so far.
1. When adding a 680 ohm resistor from +3.5V rail to the "Power ON" pin to force PSU secondary voltages on my PFC circuit does work because my mains smoothing cap voltage goes from 330VDC to 393VDC.
2. The power supply section responsible to generate the secondary voltages is operated by a L6599D. I scoped the gate drive pulses on switch on and i could briefly see some square waves but it shut down.
3. I then checked all secondary diodes for short. Only thing i saw was the Schottky diode is leaky in reverse bias but that's normal.
4. I replaced L6599D with no difference
5. I checked opto coupler and zener on the feedback circuit and found no fault. There is however a SMD chip with a marking "438" which is 3 pin and might be a SMD type KIA431, not sure could not test.
I have added pictures as needed to assist you in your diagnosis.
All tests above were done without the main connected and PSU forced on.
I have another unit that's beating me up here.
This set starts up and is in standby mode. Upon pressing the power button the set makes a relay clicking sound and then the on board "piezo speaker" which sounds when pressing any of the on board buttons starts making a long beeping sound. In the mean time the secondary voltages (those that should start up when pressing the power button) do not come up.
This is my findings so far.
1. When adding a 680 ohm resistor from +3.5V rail to the "Power ON" pin to force PSU secondary voltages on my PFC circuit does work because my mains smoothing cap voltage goes from 330VDC to 393VDC.
2. The power supply section responsible to generate the secondary voltages is operated by a L6599D. I scoped the gate drive pulses on switch on and i could briefly see some square waves but it shut down.
3. I then checked all secondary diodes for short. Only thing i saw was the Schottky diode is leaky in reverse bias but that's normal.
4. I replaced L6599D with no difference
5. I checked opto coupler and zener on the feedback circuit and found no fault. There is however a SMD chip with a marking "438" which is 3 pin and might be a SMD type KIA431, not sure could not test.
I have added pictures as needed to assist you in your diagnosis.
All tests above were done without the main connected and PSU forced on.
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