[time-nuts] HP Z3817A Reverse Engineering

Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Jan 9 18:47:31 UTC 2012


Ed Palmer wrote:
>
> On 1/9/2012 8:58 AM, Robert Benward wrote:
>> Hi Ed,
>> I just tracked down Fluke and he offered me one, and per your advice 
>> I will try and confirm the condition before purchasing from him (not 
>> that there are alternate sources) . 
>
> I have to say that fluke.l did guarantee that the E1938A was alive and 
> it was.  According to other messages on this list, he's been very good 
> about replacing defective items.
>
>> I have the schematics, but taking apart the hocky puck is another 
>> matter, I pry and pry but get nowhere.    I don't think it was 
>> designed to take apart.  What buggs me is that if I warm up the oven 
>> and stimulate the oscillator with an external signal, it will 
>> oscillate.  So it DOES work, and if I go into the puck to trouble 
>> shoot it, I probably won't find anything defective.
>
> Are you certain that the problem is inside the puck?  If I'm reading 
> the schematic correctly, the only thing in there are the crystal and a 
> few passive components.  The oscillator circuit is on the external 
> board.  A bad connection or failed component could be interfering with 
> the oscillation.  When the puck is hot, it's almost able to overcome 
> the external problem and your stimulus signal is enough to get it going.
>
Wrong, the oscillator is within the oven, its buffer amplifier is 
outside the oven.

Everything shown on the first schematic is inside the oven.

> When your E1938A is working, is it working properly, on frequency and 
> good stability?  If so, that would suggest that the crystal is okay.  
> The problem could be nothing more serious than a bad solder joint.  
> I've noticed that precision oscillators have something of a 'diva' 
> personality and can be quite temperamental.  I have an Oscilloquartz 
> BVA oscillator that takes 5 - 10 seconds to start up after you apply 
> power.
>
> Have you asked Rick Karlquist for advice on dissecting your E1938A?  
> He's an active member of this list and one of the designers of the 
> E1938A.  You might want to start a new message thread called something 
> like 'E1938A repair' to get the attention of the right people.
>
> Ed
Bruce




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