[time-nuts] HP Z3817A Reverse Engineering

[Ed Palmer]

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