[time-nuts] HP 58503A GPS time and frequency receiver - How do I determine why the ALARM LED is on?

Dr. David Kirkby (Kirkby Microwave Ltd) drkirkby at kirkbymicrowave.co.uk
Wed Jan 25 10:08:58 EST 2017

I've got an HP 58503A purchased from China a couple of years ago. It has a
bit of a hard life, having been in water at some time. But it seems to work
ok, as far as I can tell. Today there was a power failure for 5 minutes or
so. The red ALARM LED is on. It is not clear to me why, although of course
I'm aware there was a power outage, which almost certainly caused this,
although I can't be 100% sure.

Could it be that the log is full? I had a program running trying to get the
position multiple times in a loop, to get some sort of average, so I can
well believe I filled the log up. But this was a few weeks ago. The log is
clearly full .

scpi > diag:log:read:all?
Log status: Full

Log 001:19970504.00:00:00:  Log cleared
Log 002:19970504.00:00:00:  System preset
Log 003:19970504.00:00:00:  Power on
Log 219:20170107.05:30:17:  Position hold mode started
Log 220:20170107.05:30:57:  Holdover started, not tracking GPS
Log 221:20170107.05:31:03:  Survey mode started
Log 222:20170107.05:33:04:  GPS lock started

Nothing has been logged since 7th January. I know for a fact there was a
power outage on the 19th and today (25th), so I suspect the log being full
has NOT caused the ALARM light to come on. A fault, that is not logged, has
caused it.

------------------------------- Receiver Status

SYNCHRONIZATION ............................................. [ Outputs
Valid ]
SmartClock Mode ___________________________   Reference Outputs
>> Locked to GPS                              TFOM     3
FFOM     0
   Recovery                                   1PPS TI +9.5 ns relative to
   Holdover                                   HOLD THR 1.000 us
   Power-up                                   Holdover Uncertainty
                                              Predict  432.0 us/initial 24

ACQUISITION ................................................ [ GPS 1PPS
Valid ]
Tracking: 6 ____   Not Tracking: 1 ________   Time
PRN  El  Az   SS   PRN  El  Az                UTC      15:03:50     25 Jan
  5  23 186   73    24  21 252                GPS 1PPS Synchronized to UTC
 13  84 110   81                              ANT DLY  0 ns
 15  59 289   94                              Position
 20  45 245   96                              MODE     Hold
 28  51  76  104
 30  27  68   83                              LAT      N  51:39:04.155
                                              LON      E   0:46:36.381
ELEV MASK 20 deg                              HGT               +45.55 m
HEALTH MONITOR ...................................................... [
Self Test: Err   Int Pwr: OK   Oven Pwr: OK   OCXO: OK   EFC: OK   GPS Rcv:
scpi >

The self-test shows an error, but no indication what the error was, as the
log was full.

I have a fairly good idea what may have happened. Sometimes when the unit
is powered on, the voltages on the PSU appear to go out of spec. I'm not
convinced this is really happening, as a multimeter on peak hold could not
catch any glitch, but I have not tried a fast scope.

I'm just wondering if there's anything else I can do to see what caused the
LED to come on. I suspect if I execute the self-test, it will pass and the
light go out, but I'd rather find the reason before doing that.


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