[time-nuts] Troubleshooting an HP 58503A

Matthew D'Asaro medasaro at mit.edu
Sun Oct 14 18:03:29 EDT 2018

All -
     Thanks again for all the suggestions and advice I have gotten on 
this project. It ran all night without loosing lock, so I am calling it 
fixed. There is just one more order of business before I can use it, and 
that is some way of "mounting" the GPS antenna on the roof in a 
non-destructive manner, both to avoid damaging the (flat membrane) roof 
and so that I can move it if necessary. See the attached photo of what I 
have come up with. All the parts (minus the cable and antenna) came from 
Home Depot.

     The concrete block is a generic 1 sqft paver stone which cost all 
of $1.18. This is to provide a heavy base and avoid tipping. Attached to 
that is an upside-down PVC toilet flange from the plumbing section. It 
is attached with 6x stainless steel machine screws and wing-nuts that 
pass all the way through the paver and are counter-sunk on the bottom so 
that the heads won't damage the roof. Nylon spacers separate the toilet 
flange and paver block by about 1/4 inch so that water can drain if 
needed and to provide a space for the coax feed line to come out. 
Pressed into the top of the paver is a 3" to 2" reducing adapter and 
pressed into that is a 2" to 1-1/4" reducing adapter. The mast itself is 
just a 2-foot section of 1-1/4" PVC pipe. The 58532A antenna is 
apparently designed to mount over a 1-1/4" mast since its inner diameter 
is 43mm and the outside of a 1-1/4" pipe is 42mm.

     It is sitting on the back railing of the house for now but I 
ordered a 40' length of LMR-250 cable with N-connectors on both ends 
from http://www.usacoax.com/ and once that comes I can set it up for 
real on the roof with the cable running into my lab. Over and out.


On 10/13/2018 09:21 PM, Matthew D'Asaro wrote:
> It just locked!
> -Matthew
> On 10/13/2018 09:20 PM, Matthew D'Asaro wrote:
>> 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
>>>> .........................................................
>>>> [ 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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