[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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