[time-nuts] Troubleshooting an HP 58503A

Matthew D'Asaro medasaro at mit.edu
Sun Oct 14 00:20:47 EDT 2018


All -
     I think I have it fixed! The problem was a broken wire inside my 
genuine HP 58532A antenna. I was suspicious of the antenna because it 
didn't seem to matter if I had it connected or not - the 58503A behaved 
exactly the same. I confirmed my suspicions by measuring the DC current 
it drew. Zero. Something was wrong so I took it apart and measured the 
resistance between the center conductor and the board and found it to be 
infinity. As it turns out the center conductor of the micro-coax that 
connects the N-connector to the board had broken right where it was 
soldered on. It took a bit to figure out how to press the center 
conductor out of the connector, reattach the coax, and press it back in. 
To press it out I first had to unsolder the shield of the coax and then 
I could use the back of a drill-bit placed in a vice to force the center 
conductor out of the insulator. Once I had the cable reattached, I could 
press it back in by placing it over the center contact of a male 
N-connector and then screwing the two together. See the attached pictures.

     Anyway, once I had the antenna repaired it found satellites to 
track immediately - I didn't even have to set an initial date or 
location. It is about 2% of the way through its survey now and hopefully 
will have locked in by morning.

Thanks to all of you for your help!

-Matthew D'Asaro

On 10/13/2018 05:39 AM, Azelio Boriani wrote:
> Try a SYSTem:PREset first, before sending the GPS:INITial.
> On Sat, Oct 13, 2018 at 8:44 AM Matthew D'Asaro <medasaro at mit.edu> wrote:
>> 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:DATE (date)
>> GPS:INIT:POS (position)
>> GPS:INIT:TIME (time)
>>
>>       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
>> tracking
>>                      * 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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