[time-nuts] Z3805A GPS module going deaf, what modules can replace it?

[John Stone]

Hi,
  I've got a Z3805A that I bought off ebay a couple of 
years ago, and it recently started going deaf, beginning
with an apparent loss of sensitivity leading to holdovers, 
and more recently, receiver errors reported in the system 
status.

I have the Z3805A, a thunderbolt, and one of the recently discussed
KS-24361 units sharing the same GPS antenna via a four output
58536A distribution box.  I've run the Z3805A on its own
separate antenna and compared its signal levels with the
other units, and it has clearly developed some issue.
After a power cycle, I can get it going by initiating a
survey, but after a day or two of running it will lose 
all sats, and in some cases the status command will show
"GPS Rcv: Err".

I queried the hardware info on the GPS in this unit and 
from what I've gathered, it's one of the earliest motorola
Oncore GPS receivers based on the "B1121P1114" model number.
What GPS module models can I put into a Z3805A to get it 
running again?  Any tips are appreciated, including suggestions
for tests I could run on the GPS module, the power supply, or
other items that might be common failure points.

I've included the output from scpi queries below, and the 
status from the KS-24361 attached to the same antenna 
for comparison:

*IDN?
HEWLETT-PACKARD,Z3805A,3542A00943,3543B-A

:DIAG:LIF:COUN?
+29437

:DIAG:IDEN:GPS?
"COPYRIGHT 1991-1995 MOTOROLA INC.",
"SFTW P/N # 98-P39972M     ",
"SOFTWARE VER # 8          ",
"SOFTWARE REV # 4          ",
"SOFTWARE DATE  13 JUL 1995",
"MODEL #    B1121P1114     ",
"HDWR P/N # _              ",
"SERIAL #   SSG0120281     ",
"MANUFACTUR DATE 5M18      ",
"OPTIONS LIST    IB        "


Failing Z3805A system status output:
------------------------------- Receiver Status -------------------------------
 
SYNCHRONIZATION ........................................... [ Outputs Invalid ]
SmartClock Mode ___________________________   Reference Outputs _______________
   Locked to                                  TFOM     9             FFOM     3
   Recovery                                   1PPS TI  --
   Holdover                                   HOLD THR 1.000 us
>> Power-up: GPS acquisition                  Holdover Uncertainty ____________
                                              Predict  --
                                                
ACQUISITION .......................................... [ GPS 1PPS CLK Invalid ]
Satellite Status __________________________   Time ____________________________
Tracking: 0        Not Tracking: 0            GPS      08:51:14 [?] 12 Feb 2015
                                              1PPS CLK Absent or freq error
                                              ANT DLY  180 ns
                                              Position ________________________
                                              MODE     Survey:      0% complete
                                                       Suspended: no track data
                                              INIT LAT N  40:08:01.714
                                              INIT LON W  88:12:27.166
ELEV MASK 10 deg                              INIT HGT         +198.59 m  (MSL)
HEALTH MONITOR ...................................................... [ ERROR ]
Self Test: OK    Int Pwr: OK   Oven Pwr: OK   OCXO: OK   EFC: OK   GPS Rcv: Err
scpi > 


For comparison, here is what my recently acquired Z381x / KS-24361 GPSDO
says, driven from the same antenna:

-------------------------- Secondary Receiver Status --------------------------
SYNCHRONIZATION ............................................. [ Outputs Valid ]
SmartClock Mode ___________________________   Reference Outputs _______________
>> Locked to GPS                              TFOM     3             FFOM     0
   Recovery                                   1PPS TI +10.0 ns relative to GPS
   Holdover                                   HOLD THR 1.000 us
   Power-up                                   Holdover Uncertainty ____________
                                              Predict  3.7 us/initial 24 hrs
                                                
ACQUISITION ................................................ [ GPS 1PPS Valid ]
Tracking: 8 ____   Not Tracking: 2 ________   Time _____ +1 leap second pending
PRN  El  Az  C/N   PRN  El  Az                GPS      19:22:10     13 Feb 2015
  1  23 302   37    11  15 278                GPS 1PPS Synchronized to GPS Time
  4  32 269   43    18  18 138                ANT DLY  60 ns
 12  20  49   38                              Position ________________________
 14  66  30   46                              MODE     Hold
 22  53 146   39                              
 25  36  90   38                              LAT      N  40:08:00.925
 31  61 216   42                              LON      W  88:12:26.995
 32  43 310   46                              HGT              +200.94 m  (GPS)
ELEV MASK 10 deg                              
HEALTH MONITOR ......................................................... [ OK ]
Self Test: OK    Int Pwr: OK   Oven Pwr: OK   OCXO: OK   EFC: OK   GPS Rcv: OK 


Cheers,
  John Stone

-- 
NIH Center for Macromolecular Modeling and Bioinformatics
Beckman Institute for Advanced Science and Technology
University of Illinois, 405 N. Mathews Ave, Urbana, IL 61801
http://www.ks.uiuc.edu/~johns/           Phone: 217-244-3349
http://www.ks.uiuc.edu/Research/vmd/