[time-nuts] Re: help reviving Trimble UCCM-LPS GPSDO

[Wilko Bulte]

The OCXO is powered from the 5V rail of the UCCM, so I wonder how a Vref=5V would work? A bit of headroom wouod be required to make a reference circuit work.?

Wilko

> On 23 Dec 2021, at 18:15, Bob kb8tq <kb8tq at n1k.org> wrote:
> 
> Hi
> 
> It’s a pretty good bet that the Vref is 5V
> 
> Bob
> 
>> On Dec 23, 2021, at 8:42 AM, Wilko Bulte <wilko.bulte at xs4all.nl> wrote:
>> 
>> hi,
>> 
>> I am currently trying to revive a Trimble UCCM-LPS ex-telco GPSDO.
>> The model is a 57963-D according to the PCB silkscreen.
>> 
>> Got the board without its OCXO but luckily my stash of surplus I have
>> discovered a Trimble OCXO labeled 72345-86. Given that that OCXO also has a
>> label UCCM-LPS it "should work".
>> 
>> Joining the two resulted in:
>> 
>> UCCM >syst:status?
>> 
>> -------------------------------------------------------------------------------
>> 57964-86     serial number  S35DB68332   firmware ver  1.0.0.1-01 Ext
>> mode
>> -------------------------------------------------------------------------------
>> Reference Status __________________________   Reference Outputs
>> _______________
>> XX Ext Ref   : [LOS]
>>                                             TFOM     2            FFOM
>> 3
>>                                             UCCM A Status[OCXO WARMUP]
>> 
>>>> GPS: [phase:-2.8E-09, settling]
>> ACQUISITION ...................................................[GPS 1PPS
>> Valid]
>> Tracking: 8 ____   Not Tracking: 3 ________   Time
>> ____________________________
>> PRN  El  Az  C/N   PRN  El  Az                GPS      13:28:51     23 Dec
>> 2021
>> 15  71 212   37     5   6 195
>> 24  45 272   43    30   7  85                ANT DLY  77 ns
>> 17  28  97   37    19  19 124                Position
>> ________________________
>> 13  55 140   38                              MODE     Hold
>> 14  39  58   39
>> 23  33 291   44                              LAT      N  51:xxx
>> 10  17 324   40                              LON      E   5:xxx
>> 12   7 212   34                              HGT               +27.54 m
>> (MSL)
>> 
>> 
>> 
>> 
>> ELEV MASK  5 deg
>> -------------------------------------------------------------------------------
>> 
>> Command complete
>> 
>> Unfortunately it never went GPS locked. Longer story short: the pin of the
>> OCXO that (I think) should produce a Vref for the EFC circuitry produced
>> some random ~ 266mV. 
>> 
>> A quick experiment learned that the OCXO freq responds to the EFC voltage. 
>> So, looks like the Vref circuit in the OCXO has died.
>> 
>> Now the question: has anyone a working unit that they can measure the
>> correct Vref voltage from?  
>> 
>> For now I have fitted a 2.5V LM336 vref and I
>> see the EFC voltage go up and down a bit, with the output freq hovering
>> around 10MHz (+/- 4mHz roughly).
>> 
>> tia,
>> Wilko
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