Re: Loses Time


redarlington <rdarlington@...>
 

Hey guys, just to add a little info that is hopefully useful to others, I took some pictures after going through this adjustment.


I'm using a 10x probe. 100x might be better but I don't know the circuit.  I don't like loading down oscillators which could shift the frequency I'm trying to adjust.  This is a cheap but very good $120 or so frequency counter from China and is being fed around the back with a 10MHz external reference (Trimble Thunderbolt GPSDO).  This version is good out to like 6GHz.  Not a sales pitch, but my HP units can't beat it for portability.

I needed to use a pretty skinny probe to reach back to the PCB.  There's a hole for the tip of the probe to slip into if you can reach it (I couldn't with the original probe I tried).    Definitely ground your probe shield somewhere.  I'm clipped to a 1/4" jack for paddles.  The little hole right next to it has the trimmer pot/cap (can't quite tell from out here).  I used a ceramic blade adjustment tool, but plastic would likely be better only due to the fact that it's a tight fit and the ceramic isn't exactly bendy.  Plastic probably would get around the scope probe a little easier -at least with mine.

My gut feeling is to recommend some minimum warmup time like 15-20 minutes before doing this adjustment.  I turned it on and spent maybe 5 minutes looking around for the counter (lost the darn thing on the workbench -it's small!)  I've already drifted about 0.12 Hz, but this kind of thing isn't exactly a precision oscillator with double ovens and all that.   That said, I'm optimistic that my clock won't be terrible now.

-Bob N3XKB

On Thu, Jul 9, 2020 at 11:25 AM Keith_WE6R <keithtrinity@...> wrote:
Yes, sorry. The K3S clock trimmer TP is 32.768 Khz behind the VFO A knob.
Keith WE6R

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