Author Topic: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)  (Read 240395 times)

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Offline dijkmane

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #1050 on: September 19, 2019, 05:32:41 pm »
i did, it outputs 5,05V

in your pic it says 5V at the bottom of the diode, but that point is directly connected to ground.
the supply is coming elsewhere.
it seems to come somewhere from out of the OCXO.
when that ends warming up, in my unit, the voltage on top of that diode ( and so on the L ) drops from 10V to the spikey signal.

now what i did is to put a diode, directly from the output of the 3338 to the antenna, see atttached pic.

after running for 5 minutes, i see 2 sats :-), 5 mins later i have 4
solved not the way its supposed to work, but i am a step further i proces.

now awaiting the survey and a lock...

 

Online PA0PBZ

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #1051 on: September 19, 2019, 05:38:27 pm »
in your pic it says 5V at the bottom of the diode, but that point is directly connected to ground.
the supply is coming elsewhere.

I should not have written down what I thought it was but measure  :palm: Sorry about that but the good news is that you are making progress!

Keyboard error: Press F1 to continue.
 

Offline dijkmane

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #1052 on: September 19, 2019, 05:43:12 pm »
no probl.
thanks for your help.

currently 10 sats in sight, it recieved the correct date and time and GPS location coordinates

progress 1%, so i'll leave it on for a few days now
 

Offline PA0KTF

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #1053 on: September 19, 2019, 05:55:42 pm »
Well done !  ;)
 

Online PA0PBZ

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #1054 on: September 19, 2019, 06:05:30 pm »
To make up, here is the true story, a lot more complicated :)

839450-0

https://www.analog.com/media/en/technical-documentation/data-sheets/1787fc.pdf

https://www.analog.com/media/en/technical-documentation/data-sheets/4212f.pdf

[Edit] And another mistake: the LTGM is a LT1787, not LT1718 as I wrote in the picture, but the PDF is the correct one.
« Last Edit: September 19, 2019, 06:10:36 pm by PA0PBZ »
Keyboard error: Press F1 to continue.
 

Offline dijkmane

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #1055 on: September 21, 2019, 08:50:08 am »
survey done for a while now.

now how to see where it shows the output is locked to GPS ?
what to learn from this screen about my unit
« Last Edit: September 21, 2019, 12:44:06 pm by dijkmane »
 

Offline PA0KTF

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #1056 on: September 21, 2019, 03:05:33 pm »
You are not there yet.
Operation mode should say "LOCKED".
The received and locked gps satellites should be green.
 

Offline PA0KTF

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #1057 on: September 21, 2019, 03:06:24 pm »
840826-0
 

Offline dijkmane

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #1058 on: September 21, 2019, 07:50:11 pm »
ok, i see, but how to get there ?
 

Offline PA0KTF

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #1059 on: September 22, 2019, 09:56:17 am »
Some remarks:
Sometimes you receive 5 satellites, sometimes not. Check your antenna connection.
Place the antenna on a small metal plate horizontally. Gives a bit more gain.
 

Offline dijkmane

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #1060 on: September 22, 2019, 12:09:26 pm »
this is how i have it mounted
 

Offline Macbeth

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #1061 on: September 22, 2019, 10:06:04 pm »
this is how i have it mounted
That looks very shy. I face similar mounting problems...
 

Offline PA0KTF

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #1062 on: September 23, 2019, 07:25:12 am »
The antenna should have free sight to the south, positioned much further from the wall with a larger metal plat underneath.
From the picture it  looks that the antenna is blocked from the hemisphere for more than 50%.
 

Offline dijkmane

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #1063 on: September 23, 2019, 08:45:11 am »
ah, thanks.
its facing north now.

i have an idea for better placement, but have to speak to the government here at home first ( the wife.. :-) ) to explain what that "ugly thing at the wall " is for...
 

Offline dijkmane

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #1064 on: September 26, 2019, 02:38:51 pm »
ok, placed antenna on the roof.
it should have clear sight now.
( on the picture, you are looking at south direction, "front" of antenna is facing west )
on the map in LadyHeather it show it does... ?

but still it is "initializing" for over 3 days now ( allready did a new survey )
 

Offline ZigmundRat

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #1065 on: September 26, 2019, 09:55:05 pm »
I don't think you have an antenna problem...

I think you said the board is being supplied 12V. We know that's too high and could cause problems or failure. The input should be about 5.5V to 6V max. (Regardless of what the supplier says or provided.) The very first thing I would do is get this right. There are lots of pictures that show where to feed the board.

In one of your earlier posts you indicate a 'spikey' voltage at the antenna power. From your scope picture, it's spiking to 12V - (scope is on 5V/div scale). Seems suspicious doesn't it? This is obviously a problem- It may be symptomatic of a regulator cycling, trying to restart. There is clearly a power supply issue on this board and I'm not surprised you have other issues. For example, your DAC is railed at %99. (It's trying to move the OCXO frequency but it's not working. Could be a DAC failure, OCXO failure, problem reading the frequency/period, etc.)

I would suggest starting with removing the jumper wire you installed for antenna power.  Get that main power feed correct, and see if it behaves any better. If not start by checking the output of each regulator. Nothing is going to work right until the power issues are corrected.

I can try to get some readings at various points from one of my units, but it might take a bit of time. I have to clean a path to the workbench...

Attached is a picture with some measured voltage points. A couple of notes:
  • The 5V input is attached to the side of the fuse attached top the 50p FP connector
  • The 5V input ground is attached to the cap. A better place is the TP5 GND reference adjacent to the 50p FP connector
  • There is an onboard 5V to 12V boost converter for the OCXO
A place to start maybe. Hope that helps.

« Last Edit: September 27, 2019, 03:48:08 am by ZigmundRat »
 

Offline dijkmane

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #1066 on: September 27, 2019, 06:30:42 am »
...
 Nothing is going to work right until the power issues are corrected.
...

correct.
i now at least know the antenna is working, OXCO also gives output, but something seems wrong.

i'll try to dig in deeper, your picture really helps here, thanks

will let know if i find something.
 

Offline dijkmane

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #1067 on: October 05, 2019, 11:19:28 am »
I don't think you have an antenna problem...

I think you said the board is being supplied 12V. We know that's too high and could cause problems or failure. The input should be about 5.5V to 6V max. (Regardless of what the supplier says or provided.) The very first thing I would do is get this right. There are lots of pictures that show where to feed the board.

In one of your earlier posts you indicate a 'spikey' voltage at the antenna power. From your scope picture, it's spiking to 12V - (scope is on 5V/div scale). Seems suspicious doesn't it? This is obviously a problem- It may be symptomatic of a regulator cycling, trying to restart. There is clearly a power supply issue on this board and I'm not surprised you have other issues. For example, your DAC is railed at %99. (It's trying to move the OCXO frequency but it's not working. Could be a DAC failure, OCXO failure, problem reading the frequency/period, etc.)

I would suggest starting with removing the jumper wire you installed for antenna power.  Get that main power feed correct, and see if it behaves any better. If not start by checking the output of each regulator. Nothing is going to work right until the power issues are corrected.

I can try to get some readings at various points from one of my units, but it might take a bit of time. I have to clean a path to the workbench...

Attached is a picture with some measured voltage points. A couple of notes:
  • The 5V input is attached to the side of the fuse attached top the 50p FP connector
  • The 5V input ground is attached to the cap. A better place is the TP5 GND reference adjacent to the 50p FP connector
  • There is an onboard 5V to 12V boost converter for the OCXO
A place to start maybe. Hope that helps.

OK, follow up.
i've disconnected the interface PCB and connected 5V as shown in your example.
removed jumper diode to antenna power.

measured all given points, all good,
steady 4,85V at diode at antenna point, 3,3V is OK, 5V is OK, exept for 12V output from boost converter, so that one seems to be down.
output measures 4,78V, while input is 5V
12V goes to power of OCXO and to regulator U1 for antenna power

see attached pic.
now trying to find suitable 12V boost converter to mount as replacement.
 

Offline ZigmundRat

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #1068 on: October 09, 2019, 03:23:10 am »
Sounds like you're making progress. Others have provided an external 12v with success - maybe that's an option. The part is a TI PTN04050CAS - still available from several suppliers, but it's not cheap - about $16 US right now. I would think any of the other non-SMD variants would work - it's a difference of RoHS or not, through hole or not. Before spending the money though I'd remove the existing converter and feed it with 12V to be sure it started working normally.

One other thing: In reviewing the datasheet for the PTN04050C I noticed that the output voltage was set with a single resistor. That resistor is off board - so on the GPSDO somewhere. If it's missing or damaged, the regulator will revert to it's lowest output setting. It should be about 1.33k ohm but I can't find it anywhere. It might be underneath the module - maybe someone that's removed the module already can tell us.
 

Online NivagSwerdna

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #1069 on: October 09, 2019, 07:39:25 pm »
Back on p38

https://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/msg1365372/#msg1365372

I replaced the Boost Converter in mine with a like for like PTN04050CAZ which I bought at Farnell (seems Farnell are out of stock; Mouser seems to still have some).  I decided to be lazy and get the same part rather than thinking about alternatives especially given the current requirement at start-up is quite onerous.

Regards
Nivag
« Last Edit: October 09, 2019, 07:42:35 pm by NivagSwerdna »
 

Offline Macbeth

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #1070 on: October 09, 2019, 08:41:21 pm »
Ok, this is a few years ago but I also fecked up my Symmetricom by powering it with up to 12V. Apparently some similar GPSDO modules required a 12V supply for OCXO and antenna, and then dropped that to 5V on board for the logic, while this Symmetricom requires 5V (oh, and perhaps a diode drop so 5.6V) and boosts it to 12V onboard for OCXO and antenna.
 
The ludicrous price of the TI PTN04050C boost module was more than I paid for the GPSDO so feck that. I had a few 99p ebay XL6009 modules on hand so set one to 12V. I removed the voltage setting resistor (R3?) from the Symmetricom board and replaced the TI module with the XL6009.

It works great with any of my other PSU's, but for some reason the Rigol DP832 couldn't work with it. Having said that, the original TI module didn't work with the Rigol either which was why I resorted to increasing PSU voltage...
« Last Edit: October 09, 2019, 09:17:42 pm by Macbeth »
 

Offline dijkmane

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Re: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver)
« Reply #1071 on: October 10, 2019, 06:21:08 am »
i've got the old one removed.
top left pin measures 1.33kOhms to ground ( can't find the resistor itself yet... ).
exactly what the datasheet says needed for 12V output.

ordered myself a suitable clone MT3608 converter from uncle Ali for $1, awaiting shipment.

will update results.
 


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