SB-634 Question!!

[Jeff Jones]

A few years ago, while watching TV in my bedroom, I noticed time seemed to 
be flying by. Checked again a few minutes later and indeed the digital clock 
on bedroom radio had advanced several minutes during that program.
To make this brief, I traced it to a OH fan variable speed control. By 
carefully adjusting the pot, and watching the little blinging dots on the 
clock, I found the setting that caused this effect.
Jeff k3kyr
----- Original Message ----- 
From: "Bob Burns" <G3OOU at AOL.COM>
To: <HEATH at LISTS.TEMPE.GOV>
Sent: Thursday, October 22, 2009 3:02 AM
Subject: Re: [HEATH-TEMPE] SB-634 Question!!


>
>
> In a message dated 21/10/2009 23:35:48 GMT Standard Time,
> kgordon2006 at VERIZON.NET writes:
>
>> My  SB-634 works OK, but maybe too OK.the clock seems to run a bit
>>  fast!
>
> Mine too...in my SB-630
>
>> It gains about five seconds  per day.
>
> About like mine does.
>
>
>
>
> Hi Ken and All
>
> Have you tried a mains filter? Is there another fault somewhere? Five
> seconds a day suggests around 300 spikes getting through the internal 
> filter -
> probably more as those spikes that coincide with a cycle peak would
> probably not be counted anyway.
>
> The internal filter is part of a potential divider feeding half cycle 
> mains
> to the clock IC. I would check that the series resistor (8200 ohms) and
> the  filter capacitor (C208, 0.022uF) are still good and if in doubt 
> replace.
> Its  value is not particularly critical and the filter time constant is
> relatively  short compared to the period of the mains frequency. My 
> circuit
> states the  voltage across the capacitor is 14.5v pk-pk and the capacitor 
> is a
> Mylar type.  Is the problem RF based? A ceramic capacitor would in 
> principle
> be  better than a film type for very short spike suppression but that 
> would
> also  depend on the internal wiring layout, lead lengths etc.
>
>
> 73
>
> Bob
>
> Bob F Burns
> Amateur  radio callign G3OOU
> G-QRP member No. 6907
> Joint site with Crystal Palace  Radio & Electronics Club: 
> _www.g3oou.co.uk_
> (http://www.g3oou.co.uk/)
> My technical site: _http://www.qsl.net/g3oou/_ (http://www.qsl.net/g3oou/)
>
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