At 9:49 PM -0700 4/8/98, MDellesedi wrote:
>In a message dated 98-04-08 09:42:05 EDT, you write:
>
><< I think the power hadn't been connected yet at all that night, but I'm not
> positive. >>
>John,
>I noticed a few times where I turned on the switch, watched the LED go on,
>heard a slight beep and then nothing. Looking further I noticed that I had
>forgotten to plug in the power supply.

I've seen exactly the same thing. Usually my heart jumps into my throat
when this happens before I realize that the power cord is not connected :-)

>This would indicate that there must be
>a large capacitor in the primary power circuit that holds a residual voltage
>for some time.

That is correct. Mine had not been powered up for several weeks when I
tried this yesterday. Same thing: the LED blinked and a tiny sound was
heard then nothing. It is very easy to remove the power panel (four
Philips screws right on the front) and see the big capacitor and, more
importantly, a fuse.

I don't feel that tracing the circuit is worth it, but it's
>surely indicative of a situation where if someone were to plug in/out the
>keypad the capacitor's residual charge could indeed cause the problems of a
>"hot plug-in" with no power.

What I don't understand is how this can cause damage. Surely the capacitor
is fully charged during normal operation. When the power is disconnected
the capacitor may retain its charge but I would think the voltage would
remain at or below normal. Why does discharging this normal voltage cause
damage?

---
Bill Arnett "Science is a way of trying
San Jose, CA USA not to fool yourself." -- Feynman

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