[time-nuts] Z3815A

Mark C. Stephens marks at non-stop.com.au
Tue May 28 22:35:50 EDT 2013

I believe these were all rescued from the Tip (Dump, Trash) judging by the water damage and bent cases.

Mine had been tested in Japan and had approximate co-ordinates in it: 

Initially I had a OCXO communication error which I fixed by a :syst:pres
(shrug, I thought it was pretty major at the time, I can tell you!)

At the moment it's in an air scrubbed and temperature controlled room, naked, without its case. 
Both heatsinks are just slightly warm to the touch.
However the Puck is fairly warm..

I still have "Holdover Uncertainty Predict: --" which is a bit of a worry.

Also the 1PPS TI is always about -100ns relative to GPS, which is way out there..


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Stewart Cobb
Sent: Wednesday, 29 May 2013 8:13 AM
To: time-nuts at febo.com
Subject: Re: [time-nuts] Z3815A

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:


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.

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