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_pal...@sasktel.net>
To: "Discussion of precise time and frequency measurement"
<time-nuts@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_pal...@sasktel.net>
To: "Time-Nuts" <time-nuts@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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