[time-nuts] Tale of Two GPStars...

[Bruce Lane]

	After many moons, my trusty GPStar 365 (updated to a 565 through
firmware and a receiver change) finally bit the dust. Symptom: It kept
flipping between 'Coasting' and 'Recovering,' never quite reaching
'Locked.' The DAC value either ended up maxed (65534) or min'd (00000).

	Contacted Tim Gavin at Zyfer-FEI for advice. Strongest possibility:
OCXO went south. Tried manually setting the DAC for mid-point (32768)
and manually tweaking the coarse tuning on said OCXO against a
known-good 10MHz source of equal precision (translation: Another GPSDO).

	Didn't work. Tried replacing the OCXO itself, and doing the alignment
trick. Still no joy.

	Considering the lack of schematics: Emit large sigh, put unit aside,
start searching Ebay for replacement.

	Found a late-model (black case) 565-310 for a reasonable price, bought
it. Arrived a week later (yesterday at work). Opened it up, delighted to
find I got a better deal than I thought in that the thing's got a
rubidium module (FE-5650A to be exact).

	Did initial power-up/burn-in test with a local GPS antenna; Unit went
to TFOM 4 and 'Locked' within a half-hour and stayed that way all day,
DAC number just slightly above mid-point.

	However -- Date way off due to outdated Motorola UT+ receiver module.
Replaced said UT+ with the M12M drop-in module from Synergy GPS. Fired
up -- and got NO satellite tracking ID's!

	Mutter something vulgar. Do more poking around. Suddenly realize the
firmware in the replacement 565 is at 1.06, while my original unit was
at 1.08. "I wonder if..."

	Swap 1.08 firmware chip into replacement 565. Power on. Goes through
factory reset -- and comes up perfectly normal! Sat numbers appearing on
tracking report. Just checked it a moment ago (about 15 minutes after
initial re-power) and it's at TFOM 4 / Locked! And it stayed that way
through a 24-hour burn-in check.

	Conclusion: In the 565 series, you need version 1.08 firmware to
support Motorola's M12, or similar replacements.

	And I'm still amazed I lucked out with the rubidium module. ;-)

	Keep on tickin'...

-- 
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Bruce Lane, ARS KC7GR
http://www.bluefeathertech.com
kyrrin (at) bluefeathertech dot com
"Quando Omni Flunkus Moritati" (Red Green)