[time-nuts] HP Z3817A Reverse Engineering

[Ed Palmer]

Thanks for the correction, Bruce.  I made the mistake of thinking that 
the Bridge Section was the only thing inside the puck.  I should have 
looked further.

Ed


On 1/9/2012 12:47 PM, Bruce Griffiths wrote:
> 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
>