On 17 April 2010 22:22, Russell McMahon <apptechnz@gmail.com> wrote:
>> > ... some psu's have a "hiccup" mode
>> > where they shut down, pause and retry under fault conditions. If the
>> > psu is marginally overloaded it may go into that mode as things warm
>> > up.
>
>> I've also heard ticking from PSUs that are underloaded which may be a
>> similar symptom.
>
> Similar. That's "burst mode" where eg the system when running as
> throttled back as possible still charges the output capacitor at a
> rate in excess of the amount needed. eg if the amount of energy in one
> charge discharge cycle of the main inductor is greater thna the energy
> used during that cycle then the output will "pump up" if not turned
> off occasionally. So the supply cycles on and off to reduce the
> average power out.
>
> Similar to the 'hit and miss' (or similar term?) motors of yore (<
> 1940's typically) which have =A0a governor which prevents firing when
> the revs are too high. One firing stroke boosts flywheel speed enough
> that it will then run for N cycles with no spark until revs fall
> enough for another hit.
>
> Some electronic psus have two modes (in some cases integrated into the
> IC controller design) , perhaps PWM across most of the range and PFM
> at the bottom end to increase low power efficiency.
>
>
The load on the PSU is unchanged. It never used to make this noise, so
I can only assume it's related to the age/running time of the PSU.
It's a bit disapointing as it's probably less than a year old.
I think I'll have to buy a replacement then maybe I'll look at fixing
it when I have some spare time.

Thanks to everyone for all the troubleshooting advice.

Matt

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