A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)

[uncle_bob]

GPS- Display working 

Is there a link you can share to the project.

Here everything is already described.

Ok, think I found it.
 
http://www.f4ctz.fr/?lang=en

If I understand what others have/are doing they are taking the TX off the GPC receiver circuitry, not the RS232 header circuitry and it outputs a data stream in NMEA format so the above project can read, decipher and display on the LCD?

The reason I ask is there is a  number of Arduino libraries that can read/interpret NMEA data streams.

Hi

The "good stuff" is not in standard NMEA strings. It's in NMEA format proprietary messages or in other even less easy to interpret strings. .

Bob

[NivagSwerdna]

The message indicates that there is an error in generating the "every other second sync pulse". That pulse is generated off of the GPS time message and the selection process is run through the FPGA divider off of the 10 MHz oscillator. When the MCU checks the flag of "sent the pulse" against the MCU clock, that flag did not toggle as expected.

Well I know the GPS part is working since I can see tracking etc and it did a survey to hold.  I haven't watched the GPS messages as these aren't that interesting to me but perhaps I should look at the initialisation sequence.

I guess I don't know the OCXO is generating 10MHz, I can check that.  I did see a 0008 10MHz alarm once but it was quickly replaced with 0.5Hz alarm. 

Otherwise looks like the FPGA was damaged when the DC-DC converter died?

I think I'll just consider this as a scrap recovery victim and get another board.   

[davebb]

Have you got a scope or counter and go on the ocx
Dave

[NivagSwerdna]

Have you got a scope or counter and go on the ocx

Yeap. Got both of those.  When I'm next playing with this I will give it a go (really should be doing something more productive like real work!). 
However, I have checked OCXO power previously and got +12V so if it is crook (not oscillating) then I'm up a gum tree without a paddle as that wouldn't be worth economic replacement.  I'd have to chuck it down the dunny and get another.  With a bit of luck get another board, and she'll be apples. 

[davebb]

Did you tell the seller that it was not working and you wanted a replacement or refund,I did when mine was not working and sent photos of the damage and he told me he
Had sent another one out but nothing so I asked eBay to get involved and we gave more time, he contacted me and asked  me to close the claim as he had sent one,so I did not
Nothing came in the post and on the day eBay gave to see
If it had been closed, I got a nice email from paypay saying
That I had been refunded, the one he claimed  to of sent has never arrived ,get you're claim in with eBay,
Its crazy how much time we have spent on these,
Good job we were not paying some one to fix it
We would be broke,
Mine is pluged in to my Kenwood TS-2000 Radio

[NivagSwerdna]

Did you tell the seller that it was not working and you wanted a replacement or refund...

That's a work in progress.

Has anyone logged the GPS receiver output?  Which messages do you get?  (Some will be regular e.g. Position/Day etc, some will be much less regular e.g. Ephemeris changes). 
Also on start-up does the unit send messages to the receiver or does it persist its state?  Maybe it's forgotten it needs to send something (due to my use  of an inappropriate command perhaps?)

Thanks

[uncle_bob]

Did you tell the seller that it was not working and you wanted a replacement or refund...

That's a work in progress.

Has anyone logged the GPS receiver output?  Which messages do you get?  (Some will be regular e.g. Position/Day etc, some will be much less regular e.g. Ephemeris changes). 
Also on start-up does the unit send messages to the receiver or does it persist its state?  Maybe it's forgotten it needs to send something (due to my use  of an inappropriate command perhaps?)

Thanks

Hi

There is always some sort of dialog that enables / disables specific repeated messages. Depending on how this is set, you will get different messages out of any GPS module or GPSDO.

Bob

[NivagSwerdna]

There is always some sort of dialog that enables / disables specific repeated messages. Depending on how this is set, you will get different messages out of any GPS module or GPSDO.

Yes. That's why I asked if anyone had recorded it in this case.
The Furuno has some state that is retained between power cycles including estimated position and ephemeris.
Other behaviour is configured by an initial exchange of messages at power up.  I was interested in that exchange from a unit that does not exhibit the 0.5Hz Alarm condition.
$PFEC ?

[uncle_bob]

There is always some sort of dialog that enables / disables specific repeated messages. Depending on how this is set, you will get different messages out of any GPS module or GPSDO.

Yes. That's why I asked if anyone had recorded it in this case.
The Furuno has some state that is retained between power cycles including estimated position and ephemeris.
Other behaviour is configured by an initial exchange of messages at power up.  I was interested in that exchange from a unit that does not exhibit the 0.5Hz Alarm condition.
$PFEC ?

Hi

If you cut into the connections on the RX and TX on the GPS module, you can do a lot of things. The normal "timing info" port does not allow you to do variable NMEA.

Bob

[Pat Pending]

My oily Symmetricom UCCM board arrived today with C1 hanging in the air by one
ripped trace and missing a boost capacitor on the 232 interface.

My R53 is cracked in two, (resembles a mini pacman) but there is no markings of any sort to suggest its value.
I'd appreciate if someone could measure the value R53, thanks in advance.

I've attached a pic (not my brd) showing the general location.

[Vgkid]

Measured in circuit, 22 ohms. Seems small.

[gm8bjf]

Thanks for the post, I'm contemplating buying one of these modules. What is the main connector pinout?

The ribbon connector pinout is given for the Trimble UCCM unit at:

https://xdevs.com/fix/rb_lpfrs/

If you scroll through this you will find the second part of the posting is deals with the Trimble equivalent UCCM unit. As they are mechanically  identical in terms of the connectors and fixings I assume the connectors are the same. The units appear to have been designed to the same spec so I think this is a reasonable assumption. The reporting software seems to produce identical responses.

73s

Brian.

[NivagSwerdna]

The units appear to have been designed to the same spec so I think this is a reasonable assumption.

Hm.... I don't think that is correct see my earlier rather insubstantial ribbon pinout.

[NivagSwerdna]

If you cut into the connections on the RX and TX on the GPS module, you can do a lot of things. The normal "timing info" port does not allow you to do variable NMEA.

No need to cut anything.  You can just listen in pin 3 TX, pin 4 RX and pin 5 1PPS.

From GPSDO to GPS I have seen examples of these commands (not in this order or frequency)...

$PFEC,GPint,GGA01
$PFEC,GPint,GSA01
$PFEC,GPint,GSV00
$PFEC,GPint,VTG00
$PFEC,GPint,ZDA00
$PFEC,GPint,acc00
$PFEC,GPint,anc00
$PFEC,GPint,anc00,acc00
$PFEC,GPint,rrm01
$PFEC,GPint,tps01
$PFEC,GPint,tst00
$PFEC,GPrrq
$PFEC,GPrrs,1,100,1
$PFEC,GPset,M05
$PFEC,GPset,U00000000
$PFEC,GPset,Z1
$PFEC,GPset,t-000080
$PFEC,GPsrq

on the output side I see...

$GPGGA
$GPGSV
various
$PFEC
e.g.
$PFEC,GPacc,XXXXXX0XXXXXXXXXXXX00XXXXX0XXXXX
$PFEC,GPacc,XXXXXXXXXXXXXXXXXXX00XXXXX0XXXXX
$PFEC,GPanc,800106000000,00000000002000000002200000200000
$PFEC,GPanc,800106000000,00000020002220000002200000200000
$PFEC,GPanc,800106000000,00000020002222200002200000200000
$PFEC,GPanc,800106000000,00000020002222222002200000200000
$PFEC,GPrrm,2,2,00,00,00,00,+000,+00
$PFEC,GPtps,160315224627,2,0,1,000000000000,00,00,000000000000,1888,254787
$PFEC,GPtst,0,4850266005,1,C

Steady state (in survey mode at least) is for 1 Hz output looking something like...

$PFEC,GPtps,160315233257,1,0,1,150701000000,00,17,160315231107,1888,257594
$PFEC,GPrrm,2,2,00,00,00,00,+000,+00
$GPGGA,233258,****.3935,N,*****.4444,W,0,00,00.00,000005.1,M,0046.9,M,,
$GPGSA,A,1,,,,,,,,,,,,,00.00,00.00,00.00

I doubt anyone will find that very interesting.   

The protocol spec is here http://www.ko4bb.com/getsimple/index.php?id=download&file=02_GPS_Timing/Furuno/Furuno_GT8031_Protocol_Specification_Rev1.pdf

[NivagSwerdna]

Time and PPS Status

$PFEC,GPtps,160315233257,1,0,1,150701000000,00,17,160315231107,1888,257594

   Note:
The date/time based on the RTC is output after the GT-8031 is turned on until it starts
tracking a satellite.
 GPS Time is output after the GT-8031 starts tracking a satellite until it collects a UTC
parameter (including UTC offset) in the cold start condition.
 UTC is output after the GT-8031 collects a UTC parameter while tracking a satellite. 1PPS
is also output under this condition.

RAIM Status
$PFEC,GPrrm,2,2,00,00,00,00,+000,+00

Position and Time (UTC) Standard NMEA
$GPGGA,233258,****.3935,N,*****.4444,W,0,00,00.00,000005.1,M,0046.9,M,,

Positioning and Status PDOP et al.
$GPGSA,A,1,,,,,,,,,,,,,00.00,00.00,00.00

Of course none of this is really useful to most people since what we really care about is the FGOM for the timing loop and that comes out of the other serial port.  But in my case this at least proves the GPS module is behaving correctly and I see a nice 1PPS on Pin5, I also measured the OCXO and it is giving a stable 10MHz approx so I am no nearer knowing where the 0.5Hz alarm is coming from.  (But it was fun having a probe)

[Vgkid]

Measured in circuit, 22 ohms. Seems small.

Checked some others, and that seems correct.

[NivagSwerdna]

I would bet there's a way to apply battery to the board and avoid all this, but I don't know what it is yet.

The Fununo GT-8031 will accept a 3v3 backup battery across Pins 7 (BAT) and Pin 8 (GND) but according to the spec it has a typical 174uA current draw.  I think 174uA is enough to deplete a CR2032 in just a couple of months.

[davebb]

Hi I have tried a battery to see if it stopped the unit from doing a survey after power up,
It did not change this.
Thanks Dave

[NivagSwerdna]

Hi I have tried a battery to see if it stopped the unit from doing a survey after power up,
It did not change this.
Thanks Dave

Hm... OK.  I guess that is to be expected.  Survey mode is the default and I also see it sends a Z1 to the receiver.  I wonder if sending GPS Position helps? 

[NivagSwerdna]

...So, now you know *exactly* what the message means. You are no closer at all to fixing the problem....
Bob

I have now got...

Alarms:  [02A0] 0.5Hz Internal Reference EFC

UCCM-P > ALARm:HARDware?
EFC Limit Exceeded,0.5Hz,Internal Reference
Command Complete


Maybe that one can be a bit more specific?

[Pat Pending]

Measured in circuit, 22 ohms. Seems small.

Checked some others, and that seems correct.

Thanks Vgkid
I guess the low resistance value is to control reflections and waveshape seen at the end of this trace.
After some repairs getting enough power to the board looks like a big issue.
It squeals for a while until the OCXO warms up. That was at 5V5 measured between fuse and ground.
I could adjust it higher but there's a linear regulator producing 3V3 from that and I didn't want to overdo it. Just how high can Vin be ?

[Vgkid]

Dont go over 6. It will shut off, both of mine squel.

[NivagSwerdna]

Hey!  I think I might have found something!  I don't seem to have a C94
Please can someone suggest a value for this component.

I can see from https://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/msg846858/#msg846858 that they do have a C94.  I notice that their board is missing C122 which I do have.

[Pat Pending]

Hey!  I think I might have found something!  I don't seem to have a C94
Please can someone suggest a value for this component.

c94 (like C73 closeby) go to the same internal power planes, it's a decoupling cap.

[NivagSwerdna]

c94 (like C73 closeby) go to the same internal power planes, it's a decoupling cap.

Thanks!  Might not be the explanation of my 0.5Hz Alarm then but I'll put something there anyway and see.