SB-634 Question!!

[Bob Burns]

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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