[time-nuts] Z3815A

[Stewart Cobb]

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