Author Topic: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver) (Read 552265 times)

Astralix · « **Reply #1025 on:** January 30, 2019, 08:14:43 am »

Thanks again!
I cannot see any Samsung available these days, but a some EPSON based units show up once in a while. I'll try that one too. But as soon as a Samsung pops up, I try my luck on it.

Question to all: Does anyone know one or two of the manufacturers, that developed the UCCM unit? Cause Trimble and others did build the units to "customer specifications", but cannot tell any names due to existing contracts...

In the former mentioned polish forum there is a picture showing a resistor / transistor position, that could be cut. As a result, the 10MHz signal is not attenuated anymore if the units feels unhappy. http://mikrofale.iq24.pl/podglad_posta.asp?id_komentarza=2544131
If I get my unit syncing it's OCXO to the GPS, I will probably turn R302 sideways and connect it to 3V3 or GND, whatever needed, to have the output always on. If I get the unit to a point, where it will output a signal, it will probably still stay in alarm cause of the LINK thing. So I can use the former driver signal at R302 to drive my own LED showing 10MHz ready and stable.

73!

texaspyro · « **Reply #1026 on:** January 30, 2019, 04:41:16 pm »

There are at least 2 sellers on Ebay right now. Search for: Samsung GPSDO

Astralix · « **Reply #1027 on:** January 31, 2019, 12:10:31 pm »

Interesting!

The Samsungs (yes, found them

) seem to be mounted upside down, while the older Trimble where mounted oven upside. I have heard that someone had an issue with the Trimble held upside down as some important parts fell from the PCB inside the oven. AFAIF the heating MOS-FET unsoldered itself.

The seller also adds a short FFC cable and a matching breakout board. And there are "more than 10 available".

As my FFC cables already arrived, I just need to wait for the breakout boards and could do some more reverse engineering. Then I decide if I buy another unit.

JBeale · « **Reply #1028 on:** February 26, 2019, 09:40:40 pm »

Quote from: Astralix on January 31, 2019, 12:10:31 pm

The Samsungs (yes, found them ) seem to be mounted upside down, while the older Trimble where mounted oven upside. I have heard that someone had an issue with the Trimble held upside down as some important parts fell from the PCB inside the oven. AFAIF the heating MOS-FET unsoldered itself.

I was thinking about an Ebay GPSDO, but if they include any semiconductor parts that are actually intended to run hot enough to sometimes melt their solder, I think I'll pass.

Sparky67 · « **Reply #1029 on:** July 27, 2019, 11:11:28 pm »

I bought a 'GPSDO Built-in Symmetricom Inside' box from eBay some weeks ago. It was in nice condition and worked. At least, for a while. It stopped receiving signals from the GPS satellites and something was rattling around inside. So I took the unit out of its box and found this:

Does anyone have a similar unit and can tell me what is marked on their unfrazzled component please, so it can be replaced? It is C3.

Many thanks.

Martin

PA0KTF · « **Reply #1030 on:** September 17, 2019, 08:23:40 am »

I checked the voltage regulator on the Symmetricom board, type 3338. See attached picture.
I think this is an ADP3338 from Analog Devices. I looked at the specs (see attached data sheet).
The maximum allowed input voltage is 8.5 Volt. However the measured input voltage on the board is 12 Volt, so way above this spec.
To protect the device I added a 78L08 voltage regulator in series to avoid any damage.
Does anybody have the same experience or any comment ?

dijkmane · « **Reply #1031 on:** September 17, 2019, 06:42:10 pm »

currently working on a Symmetricom GPSDO with Furuno Board.

unit had been on for several days, but it won't find any satelites.
PPS and 10MHz outputs are working, so the OCXO is ok.

after reading ( part of ) this thread, i tried some commands with putty and the serial connection.
did factory reset and read out the status.

noticed that my antenna voltage is about 190mV, so started there with further analysis.
( all other screenshots in this thread show voltages of about 5V )

put the antenna to my probe on the scope and got attached readout.
there are spikes, 10msec long and about 10V every 250msec.
for the rest a flat line.

is this normal behaviour, or is there something wrong with the antenna supply ?
how to proceed?

PA0PBZ · « **Reply #1032 on:** September 17, 2019, 07:02:37 pm »

Is that with or without an antenna connected? If it is with disconnect it and measure again, it is certainly not normal, it should supply a steady voltage for the amp built in to the antenna.

PA0KTF · « **Reply #1033 on:** September 17, 2019, 07:27:12 pm »

to: dijkmane

Abnormal behaviour.
Which antenna are you using ?
Are there any LED's working at the backside of the board ?
They shoud be green and blinking.
There is only a 10 MHz output at the sma connector when the unit is locked to gps.

dijkmane · « **Reply #1034 on:** September 18, 2019, 06:55:56 am »

using standard supplied antenna.
disconnected or connected, does not make difference, see attached screens
LED's on frontside of the unit DC and ACT are on, 1PPS is flashing
on PCB the LED's DS2 is flashing and DS3 and DS4 are on, DS1 is off

10MHz outputs on frontside and the 1PPS do give signal

PA0PBZ · « **Reply #1035 on:** September 18, 2019, 07:08:58 am »

What is the deal with the bodge wire? Can you post a picture of the other side of the board?

dijkmane · « **Reply #1036 on:** September 18, 2019, 07:32:36 am »

don't know, this is the way its delivered.
wire goes to interface PCB on D3 ( on top of picture ), where it ends at a +, see attached pic

i measure about +2V at D3

PA0KTF · « **Reply #1037 on:** September 18, 2019, 08:42:54 am »

You say it goes to the interface board. So there is an interface board.
Your antenna pulse looks not synchronised with the 1 PPS pulse.

Can you test the symmetricom board seperately ?
And if so can you hookup the rs232 interface (real rs232, not TTL rs232) near the 1 pps smc connector ?
There is a very nice program called Lady Heather from KE5FX which shows the GPS data received.
It shows if the GPSDO is locked, how may gps satellites are received, etc. etc.

dijkmane · « **Reply #1038 on:** September 18, 2019, 12:15:26 pm »

thats why i started, it doesn't find any sats...

PA0PBZ · « **Reply #1039 on:** September 18, 2019, 12:23:22 pm »

It will not find any sats if you have an antenna with a preamp that is not powered. I will check mine tonight to see where the antenna power comes from, if I remember correctly it was quite simple. I still fail to see where the pulses come from.
So you did buy a package and not just the pcb? Do you have warranty on that? Do you have a link to what you bought?

dijkmane · « **Reply #1040 on:** September 18, 2019, 12:32:27 pm »

i am still in dispute with the seller about sending me a not working item, but that is taking almost 3 months now.
in the meantime i am trying to find out what is wrong with it...
ebay item : ebay.nl/itm/Symmetricom-GPS-Receiver-10MHz-1PPS-GPS-Disciplined-Clock-GPS-Ant-GPSDO/264358903137

PA0KTF · « **Reply #1041 on:** September 18, 2019, 01:08:31 pm »

What is the voltage on the antenna input without gps antenna ? It should be 5 Volt.
Can you measure the current into the gps antenna ?

PA0PBZ · « **Reply #1042 on:** September 18, 2019, 01:26:52 pm »

Quote from: PA0KTF on September 18, 2019, 01:08:31 pm

What is the voltage on the antenna input without gps antenna ? It should be 5 Volt.
Can you measure the current into the gps antenna ?

This is without the antenna connected (See his earlier post)

PA0KTF · « **Reply #1043 on:** September 18, 2019, 03:10:09 pm »

Do you measure about 5 Volt DC on this connector ?

PA0KTF · « **Reply #1044 on:** September 18, 2019, 03:15:08 pm »

See attachment

dijkmane · « **Reply #1045 on:** September 18, 2019, 04:07:01 pm »

nope,
same signal as on screen
small pikes.

on that connector there is a small cable that goes to frontpanel for antenna connection.
cable is good, no short and good connection

PA0PBZ · « **Reply #1046 on:** September 18, 2019, 05:27:34 pm »

As promised an overview of how the GPS antenna is powered. The 5V comes directly from the U1 (3338) rightmost pin to the anode of CR1. From there it goes trough L2 to end at the GPS antenna connector. The RF signal from the antenna connector reaches the receiver via DC block C3. You should be able to find the problem now, also see attached picture.

dijkmane · « **Reply #1047 on:** September 19, 2019, 01:16:18 pm »

thnx.
where in the pic it says 5V, mine is allways 0V there.
other side of this diode, it reads 10V for about 10-15sec, then it drops to the spike signal as in my pics.

RF and antenna disconnected while measuring

OCXO is getting pretty warm and gives output.

other side of the board, where flat cable comes in i found some regulators for 5V and 3V3, both give steady output.
12V comes through flatcable from interface board, whole thing is not using more than 600mA.

have to dig in deeper...

PA0KTF · « **Reply #1048 on:** September 19, 2019, 01:27:53 pm »

Did you check the 3338 regulator ?
See my previous post.

dijkmane · « **Reply #1049 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...


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Author Topic: A look at my Symmetricom GPSDO / 10MHz reference (OCXO + Furuno receiver) (Read 552265 times)

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