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

[Bob kb8tq]

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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