[time-nuts] Troubleshooting an HP 58503A

Matthew D'Asaro medasaro at mit.edu
Sat Oct 13 00:16:03 EDT 2018

All -
     I have made substantial progress on my HP 58503A, but I am not 
quite there yet. By watching the internal lights and the data on the 
processor bus I could see that the CPU was starting to boot and then 
restarting every ~15 seconds. Furthermore, the reset circuit didn't seem 
to be working right. Sometimes when I power cycled it the front panel 
lights would flash to indicate a self-test, other times they would not. 
This seemed to indicate that the system was not being reset correctly on 
start-up. More telling, when I manually triggered the reset generator 
chip, the system would not ever flash its front panel lights even though 
I could see that the CPU was being reset per the internal lights.

     The problem, as it turned out, was more mechanical than electrical. 
As shown in the attached photo, someone had put the case back together 
with a screw that was too long! It dug into the board and cut two 
traces, one of which was the reset line for the UART chip (and probably 
some other chips as well - I didn't fully trace the line). Once I 
repaired these two traces (red wires in my picture) it booted right up 
and even passed its self-test!

     However, the story does not end there. I now have it booting and 
appearing to "work" but I can't get it to track satellites. I manually 
set the location, date, and time with the following commands:
GPS:INIT:POS (position)

     I then setup the unit (inside, but with the GPS antenna near a 
window) and left it turned on overnight. However, no dice. The system 
does not display errors but won't track any satellites. Here is the 
results of a SYSTEM:STATUS? command:

scpi > system:status?
------------------------------- Receiver Status 
SYNCHRONIZATION ........................................... [ Outputs 
Invalid ]
SmartClock Mode ___________________________   Reference Outputs 
    Locked                                     TFOM 9             FFOM     3
    Recovery                                   1PPS TI  --
    Holdover                                   HOLD THR 1.000 us
 >> Power-up: GPS acquisition Holdover Uncertainty ____________
                                               Predict  --

ACQUISITION .............................................. [ GPS 1PPS 
Invalid ]
Tracking: 0 ____   Not Tracking: 14 _______   Time 
                    PRN  El  Az  PRN  El  Az   UTC 05:08:22 [?] 11 Oct 2018
                    * 1  -- ---  *10  -- ---   GPS 1PPS Invalid: not 
                    * 2  -- ---   16  35  50   ANT DLY  0 ns
                    * 3  -- ---  *23  55 129   Position 
                    * 5  -- ---   26  10  41   MODE Survey:      0% complete
                    * 6  -- ---   27  21  96 Suspended: track <4 sats
                      7  57 267   30  25 257   INIT LAT N 47:42:01.770
                    * 8  13 127                INIT LON W 122:16:26.770
                      9  81 141                INIT HGT          +20.00 
m  (MSL)
ELEV MASK 10 deg   *attempting to track
HEALTH MONITOR ......................................................... 
[ OK ]
Self Test: OK    Int Pwr: OK   Oven Pwr: OK   OCXO: OK EFC: OK   GPS 
Rcv: OK
scpi >

Is there anything else I can try?

Thanks in advance,
Matthew D'Asaro

On 10/07/2018 12:26 AM, Mark Sims wrote:
> The 58503A needs a null-modem pinout serial cable to connect to a PC. The baud rate defaults to 9600:8:N:1
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> time-nuts mailing list -- time-nuts at lists.febo.com
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