I have three 1998 SkyHawk ATX PSUs model SH250A8 that have a weird design of the auxiliary power supply (which is rated 0.8A).
There is no additional transistor on the primary heatsink and also no additional transformer. +5VSB is supplied by 7805 regulator running from the +12V line somehow?! On the secondary side, there is a branch from the +12V line that leads through a diode (and maybe some resistor) to 7805's input and there is a 100uF/50V cap there. When in soft-off mode, the PSU produces a buzzing sound and there are some voltages on all outputs. When it gets old, that 100uF cap goes bad, the buzzing sound gets louder and output voltages bigger. One of them now produces 5.6V on the +12V line when off!
When I replaced the cap with 220uF/25V, it became much quieter and the voltage on the +12V line was "only" about 1.2V. It looks like pretty bad design to me. These PSUs are not Deer (as newer models are) and are quite powerful - I use one for testing purposes (I always unplug it and never leave it in soft-off). But this auxiliary power supply design is really braindead
There is no additional transistor on the primary heatsink and also no additional transformer. +5VSB is supplied by 7805 regulator running from the +12V line somehow?! On the secondary side, there is a branch from the +12V line that leads through a diode (and maybe some resistor) to 7805's input and there is a 100uF/50V cap there. When in soft-off mode, the PSU produces a buzzing sound and there are some voltages on all outputs. When it gets old, that 100uF cap goes bad, the buzzing sound gets louder and output voltages bigger. One of them now produces 5.6V on the +12V line when off!
When I replaced the cap with 220uF/25V, it became much quieter and the voltage on the +12V line was "only" about 1.2V. It looks like pretty bad design to me. These PSUs are not Deer (as newer models are) and are quite powerful - I use one for testing purposes (I always unplug it and never leave it in soft-off). But this auxiliary power supply design is really braindead
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