[time-nuts] Using a frequency synthesizer replacement for motherboard oscillator

Mark Allwright mark.allwright at shaw.ca
Sat Dec 1 19:34:43 UTC 2012

You need to replace the clock that drives the CPU; in some designs this was 
the 14.318 MHz oscillator that would be multiplied up to the required 
frequency.  You could also replace the 14.318 MHz oscillator with a TCXO or 
better; make your own simple OCXO around a 14.318 MHz oscillator or lock a 
14.318 MHz oscillator to a high stability reference oscillator (Rb, GPSDO 
etc.).  You would need to do some circuit surgery on the PC motherboard for 
this type of stuff.

Some links:

<http://www.moshier.net/#Rubid_pc> Lock 14.318 MHz to Rb
<http://www.wraith.sf.ca.us/ntp/#ocxo-osc> Simple oven
<http://www.techlib.com/electronics/ovenckts.htm> More simple oven circuits
<http://www.febo.com/pages/soekris/index.html> John's note for the Soekris 
and clock hacking




Mark Allwright, VE6NTP

-----Original Message----- 
From: Sarah White
Sent: Friday, November 30, 2012 5:10 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Using a frequency synthesizer replacement for 
motherboard oscillator

On 11/30/2012 6:30 PM, Eric Garner wrote:
> the actual RTC on modern (Intel based) PC's is driven from a standard
> 32,768 Hz crystal attached to the PCH. some of them are in incredibly 
> small
> packages now instead of the old tuning fork-in-a-can ones. peeling off the
> load caps and crystal from the board would allow you plenty of spaces to
> tack down a lead from an external synthesizer.

Yeah, the one on the (Soekis) example was pretty small. So far none of
of the replies have indicated that anyone on here has experience beyond
an embedded system.

Mostly I started this thread because there have been a few with people
discussing implementing NTP on embedded microcontrollers, arduino, etc.
and I was thinking of doing it from the other side (turning a nice-ish
server into a rock-solid timekeeper)

Thanks so far everyone. Really impressed that I already managed to get
4x replies so quickly :)

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