[time-nuts] Z3815A

Azelio Boriani azelio.boriani at screen.it
Tue May 28 19:16:01 EDT 2013

I'm powering my Z3815A from 48V, the telecom standard voltage.

On Wed, May 29, 2013 at 12:12 AM, Stewart Cobb <stewart.cobb at gmail.com> wrote:
> Your Z3815A may need more cooling than it's getting, especially if you have
> it resting "horizontally" as it looks like it should.  I bought one of
> those "kits from China" about a year and a half ago.  Powered it up, waited
> for it to lock ... and it was dead within a week, with the unmistakable
> smell of overheated electronics.  One of the Vicor power bricks inside
> (probably) overheated and shorted out.  Here's what I learned:
> The Z3815A board was designed to go into a VXI-like mainframe, with a
> carefully specified amount of cooling airflow.  I think that particular
> board was designed to require that airflow, and overheats without it.
> There's a group in Australia which has experience with these boxes, and I
> got the impression from my contacts with them that they see the Vicor
> bricks fail pretty regularly.  That would imply that they're not getting
> the cooling they need, because Vicor bricks in other applications are
> pretty reliable in my experience.
> You can see a photo of the original Z3815A on TVB's website here:
> <http://www.leapsecond.com/museum/z3815a/>
> The Z3815A I got from China was in a different case, just two bent pieces
> of sheet aluminum.  The case _looks_ official, with the right label on the
> front and silkscreen on the back.  But the board inside had a lot more crud
> and corrosion than the nice clean case did, and parts of the plastic edge
> connector on the back of the board were broken.  Worst of all, the coaxial
> cable from the antenna connector ended in a one-inch flying lead soldered
> to the board.  The "shield" of the coax cable ended in another flying lead,
> soldered to ground somewhere else.  (Any RF engineers reading this are
> probably cringing now.)  I'm pretty sure that no one at HP designed or
> approved that connection.  Once I saw it, I understood why the GPS receiver
> appeared to be "deaf."  Even connected to a very good antenna, it never saw
> more than 4 satellites, and even those had weak signals.
> Did someone in China find a cache of bare Z3815 boards in a scrapyard
> somewhere, and fab an official-looking case to match?  I don't know, but it
> might be the way to bet.  Meanwhile, take the lid off your Z3815A and feel
> the heatsinks on the power bricks.  If they're too hot to touch, they're
> too hot; give them some air.
> Cheers!
> --Stu
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