[time-nuts] HP Z3817A Reverse Engineering

Ed Palmer ed_palmer at sasktel.net
Mon Jan 9 16:26:13 UTC 2012


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.

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

> Bob
>
>
>
> ----- Original Message ----- From: "Ed Palmer" <ed_palmer at sasktel.net>
> To: "Discussion of precise time and frequency measurement" 
> <time-nuts at febo.com>
> Sent: Sunday, January 08, 2012 10:07 PM
> Subject: Re: [time-nuts] HP Z3817A Reverse Engineering
>
>
>> Hi Bob,
>>
>> I bought mine on eBay from fluke.l for about $114 (including 
>> shipping).  I don't know if he has any more.
>>
>> He didn't get positive feedback from me.  His pictures showed a 
>> reasonable, used unit.  The unit he shipped was dented badly enough 
>> that it was slightly crushed and appeared to have been out in the 
>> rain.  It does work, but the E1938 seems to be taking a long time to 
>> settle down.  I hope the crystal wasn't damaged when it took the hit 
>> that dented the case. There is no physical damage to any of the 
>> boards.  I've dealt with him before and was surprised and 
>> disappointed that he didn't describe the condition better.  Buyer 
>> beware.
>>
>> As for your 'lazy' E1938, have you grabbed the schematics and circuit 
>> description from
>>
>> http://www.prc68.com/I/HPE1938.shtml ?
>>
>>
>> Ed
>>
>>
>> On 1/8/2012 5:58 PM, Robert Benward wrote:
>>> Hi Ed,
>>> May I ask where did you get your STLN4096A and what you paid for 
>>> it?  Do they have any more?
>>>
>>> My E1938 recently crapped out.  If I put a substitute 10MHz near the 
>>> first buffer, the PIC processor comes alive, then I can remove the 
>>> 10MHz and it begins to oscillate on it's own.  I can quickly recycle 
>>> power and it still oscillates.  Let it cool down and I need to 
>>> repeat the "stimulus" procedure. Anybody have any ideas?
>>>
>>> Thanks,
>>> Bob
>>>
>>> ----- Original Message ----- From: "Ed Palmer" <ed_palmer at sasktel.net>
>>> To: "Time-Nuts" <time-nuts at febo.com>
>>> Sent: Sunday, January 08, 2012 12:20 PM
>>> Subject: [time-nuts] HP Z3817A Reverse Engineering
>>>
>>>
>>>> I recently purchased a Motorola STLN4096A with the HP E1938A 
>>>> oscillator. I bought it for the oscillator only.
>>>>
>>>> Then I got intrigued by the HP Z3817A GPSDO that's included.  I've 
>>>> reverse engineered most of it and I've got it running.  The 1 PPS 
>>>> is really good ( 1000 measurements, Std. Dev. of <200 ps, min to 
>>>> max range of <1.5 ns) and the HUP is very slowly dropping 
>>>> (currently at 13 us after ~1.5 days) as the oscillator works out 
>>>> the kinks after it's long sleep.  It's dropping much slower than my 
>>>> Z3801A did when I first turned it on.
>>>>
>>>> There's one input that I haven't been able to figure out.  I've got 
>>>> data in and 1 PPS in from the GPS receiver.  Everything seems to be 
>>>> working so I'm at a loss what that the other input could be for.  
>>>> There are no clues to it's function because it appears to go into 
>>>> one of the Xilinx chips.
>>>>
>>>> Does anyone have any more info on the unit?  Has anyone figured out 
>>>> the other input?
>>>>
>>>> I have searched the net and the archives.  There's very little info 
>>>> or discussion on this unit.
>>>>
>>>> Ed



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