Re: Chirping //e

[pausch@saaf.se (Paul Schlyter)]

In article <1C5S8.3011$ZM3.850405@news20.bellglobal.com>,
Don  Kelly <don.kelly@sympatico.ca> wrote:
 
> The Apple II (all models) used a switching power supply. These power
> supplies use high speed (frequency) switching to generate the required
> output voltages (very simplistic explanation) which allows for smaller
> components, more stable voltages and a bunch of other advantages including
> cheaper construction.
 
A non-switching power supply works like this: the mains AC voltage is fed
directly to a transformer, when thus works at 50 or 60 Hz (depending on
where you live).  After the transformer, the AC is rectified into DC
and may also be stabilized.
 
A switching power supply works like this: the mains AC voltage is
directly rectified into DC, then it's converted into higher-frequency
AC (many kHz).  That higher-frequency AC is fed to a transformer.
The AC output from the transformer is then rectified/etc.
 
Thus the major difference between the switching and the non-switching
power suply is the frequency the transformer works at: 50/60 Hz for
a non-switching power supply; many kHz for a switching power supply.
At the higher frequency the tranformer can be made smaller and still
handle the same amount of power.
 
A switching power supply is of course more expensive than a
corresponding non-switching power supply -- but it is considerably
smaller and lighter.
 
> Anyway it is not uncommon to hear these power supplies sing (especially
> older ones) when transformers are not screwed down tight or the transformer
> cores are loose. Equally it is not uncommon to hear them chirp when turned
> on and/or off as the switching frequency builds up or falls off for similar
> reasons. This does not normally impact their operation, its just annoying.
> 
> Switching supplies often employed varesistor which, in older versions when
> they were "new" technology, had a tendency to partially come apart.
> Basically they were a special carbon disk (small one) between two metal
> contacts  ( ---|---) and the contacts came unglued from the disk.
> Particularly during startup these components would chirp (loose again)
> though normally they worked fine. Occasionally they went up in smoke when
> the "looseness" of the connections generated excessive heat.
> 
> If it was up to me I would run the chirpy power supply until it failed, if
> ever.
> 
> 
> "Simon Williams" <ludditetech@mac.com> wrote in message
> 9f61cf69.0206250424.10b92aae@posting.google.com">news:9f61cf69.0206250424.10b92aae@posting.google.com...
>> I have a //e Platinum which makes an gives out a high 'chirp' when I
>> shut it down. I disconnected the speaker and disk drives and still it
>> cheeps at me... sounds like it may be coming from the power supply,
>> but it's one of those sounds that's really hard to pinpoint.
>> Thought? Theories?
>>
>> Assuming the P/S is on it's way out, can I swap in one from a beige
>> //e?
 
-- 
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Paul Schlyter,  Swedish Amateur Astronomer's Society (SAAF)
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