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

[uncle_bob]

This seems like a huge co-incidence... too much of a co-incidence, there really isn't much to age on that module.  I wonder if the DC-DC converter fail is actually a symptom of a problem with the OCXO from too long without use or similar?  Maybe there is a lesson to be learned as to how to power these on for the first time?

Or the seller or person before them toasted them by not knowing the required voltage and using a high voltage power supply when testing.

Hi

... or ... The piece of gear these originally were used in had a bulk switcher that tended to fail with a high output voltage. I've seen that both in the field and on shop floors. In most cases there are an amazingly large stream of returned parts before the problem is tracked down.

Bob

[grumpydoc]

One looks OK, as seems common the other is missing the antenna connector but I haven't spotted any other damage (yet).

Ah, rats - C1 partially ripped from the board and flapping in the breeze, taking the vias with it on one board. the other looks like it might be OK if I remove it and superglue the tracks (and the cap) back to the board.

Previously if tracks have lifted I have had some luck with superglue - what does everyone else use, is there anything better?

[Bryan]

Has anyone had any luck in determining if there is the capability to read the data from the receiver in NMEA format. I saw this nice Arduino library, but no luck getting it to return any data. So far my only luck has been in receiving data using the commands at the start of the thread via the RS232.

http://arduiniana.org/libraries/tinygpsplus/

[hs3]

OK... I'm going to need some help!  I attached 5V from my bench supply...

The unit draws only 220mA and it appears the low voltage side works...  (with no antenna attached) I have DS3 solid green, DS4 solid red and DS2 flashing green.

What do you think? PTN04050CAS knackered?

What kind power supply did you use when you tried to power it up? Did you try with any higher voltage?

I didn't have luck powering it up with 5V when I tested. It seems to have quite high inrush current at lower voltages.

Here you can see couple measurements I made with my unit:
https://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/msg849591/#msg849591

Was the DC/DC converter making any sound when you tried it? In my case it had this whining sound when it didn't start up with lower voltage.

[Macbeth]

I found that using my DP832 with 5-5.5v and winding it up to even 3A it wouldn't start. It would clamp the volts to ~3V and whistle. I determined the TI DC/DC converter was faulty and replaced with an ebay XL6009 after finding the TI part on AliExpress but the seller being a charlatan.

Strangely I can't power it up with the DP832 even at 5V 3A, but using any other PSU I have no problem, 5V @ 1.7A seems to be needed to start it. It settles down very quickly so it is a high inrush current.

Maybe my DP832 is faulty?  Works great with everything else though. All my other PSU's go into the same whistling and 3V if powered with less than 1.6A.

Of course substituting the XL6009 muddies the waters.

[NivagSwerdna]

What kind power supply did you use when you tried to power it up? Did you try with any higher voltage?

Benchtop TTi EL302RD Dual Supply.  5V limit to 2A

Was the DC/DC converter making any sound when you tried it? In my case it had this whining sound when it didn't start up with lower voltage.

Initially there was some whine but it was short lived and then settled to 150mA or so at 5V and 12V converter now seems to be straight through.
The 5V side seems to work OK.  Attached PC to the RX/TX/GND and can talk to the device.  Seems it used to hang out on top of a block of flats in down town Yokohama, Japan.
Next step is +12V to what was pin 4 of the converter and I also need to solder on a antenna connector to J2

[Macbeth]

Initially there was some whine but it was short lived and then settled to 150mA or so at 5V and 12V converter now seems to be straight through.
The 5V side seems to work OK.  Attached PC to the RX/TX/GND and can talk to the device.  Seems it used to hang out on top of a block of flats in down town Yokohama, Japan.
Next step is +12V to what was pin 4 of the converter and I also need to solder on a antenna connector to J2

Yep, sounds familiar. I had it running off +5 and +12 from the DP832 no problem when the onboard TI boost module failed and I removed it. I also found the antenna voltage is whatever you power it with minus a typical 0.6 diode drop. So 5V - 5.5V is what you want considering a typical GPS antenna is 3.3V-5V rated.

[hs3]

Strangely I can't power it up with the DP832 even at 5V 3A, but using any other PSU I have no problem, 5V @ 1.7A seems to be needed to start it. It settles down very quickly so it is a high inrush current.

Maybe my DP832 is faulty?  Works great with everything else though. All my other PSU's go into the same whistling and 3V if powered with less than 1.6A.

It seems your experiences with DP832 match quite closely with my experiences with DP832 and this Symmetricom unit.

Maybe the DP832 current limiting kicks in quicker than the other supplies? In those scope captures there were spikes up to 8A when the converter tries to start.

I believe I have seen it mentioned somewhere that the correct voltage for the Trimble version would be about 6V. So could be similar for this Symmetricom version. So maybe 5V is just too much below the intended supply voltage for these.

What kind power supply did you use when you tried to power it up? Did you try with any higher voltage?

Benchtop TTi EL302RD Dual Supply.  5V limit to 2A

I think I have EL302D somewhere too. Maybe I should try with that too sometime later to have another data point.

[hs3]

I also found the antenna voltage is whatever you power it with minus a typical 0.6 diode drop. So 5V - 5.5V is what you want considering a typical GPS antenna is 3.3V-5V rated.

One possibility is that the antennas used in the original application with these have used higher supply voltages than 5V too so these may not be the best fit with the typical low voltage GPS antennas that way.

[Macbeth]

It seems your experiences with DP832 match quite closely with my experiences with DP832 and this Symmetricom unit.

Maybe the DP832 current limiting kicks in quicker than the other supplies? In those scope captures there were spikes up to 8A when the converter tries to start.

I believe I have seen it mentioned somewhere that the correct voltage for the Trimble version would be about 6V. So could be similar for this Symmetricom version. So maybe 5V is just too much below the intended supply voltage for these.

Oh, believe me, I tried starting my board with 6V and limiting the amps and raising them only to find the DP832 clamping down at ~3V. Even dialling in 12V supply didn't help, the DP832 only supplied ~3V and the TI boost module would be ringing. I measured the VIN at the board with a DMM and sure enough it was clamped low no matter what you set the DP832 at.

That was with the TI module. Remove it and power with seperate 5V and 12V from the DP832 and it works great. But I switched the TI module for a cheap XL6009 module and found the same clamping the voltage low and oscillating when powering with 5-6V and 3.2A on the DP832.

Using my HP 6632B and my cheap ass Tenma PSU's I observed the same 3V clamping behaviour if powered with less than 1.6A CC, even when winding the current limit up to 5A.

I found starting with >=1.7A @ 5V it works just fine. Just not with any V or A on the DP832 

[hs3]

Oh, believe me, I tried starting my board with 6V and limiting the amps and raising them only to find the DP832 clamping down at ~3V. Even dialling in 12V supply didn't help, the DP832 only supplied ~3V and the TI boost module would be ringing. I measured the VIN at the board with a DMM and sure enough it was clamped low no matter what you set the DP832 at.

I believe

My comment about maybe needing more than 5V was intended more generally about these modules as in some cases I'm not sure if much higher than 5V supply has been used. Maybe it has but it haven't been clear to me.

But I think the additional details you provided how it behaved in your case are useful.

That was with the TI module. Remove it and power with seperate 5V and 12V from the DP832 and it works great. But I switched the TI module for a cheap XL6009 module and found the same clamping the voltage low and oscillating when powering with 5-6V and 3.2A on the DP832.

Using my HP 6632B and my cheap ass Tenma PSU's I observed the same 3V clamping behaviour if powered with less than 1.6A CC, even when winding the current limit up to 5A.

I found starting with >=1.7A @ 5V it works just fine. Just not with any V or A on the DP832 

Ah so the XL6009 solution isn't working with the DP832 at all?

I haven't tested with the XL6009 so can't say much about it but I suppose that if it is a challenging load with the original TI converter then with the XL6009 it might be too.

Also regarding DP832 I think I have seen it mentioned in other places that it has been quicker to limit current than some other supplies even if the average current is not yet close to the current limits. So your DP832 may not be behaving differently than other DP832 units. But any other opinions/comments on this are welcome.

[Bryan]

GPS- Display working 

Is there a link you can share to the project.

[NivagSwerdna]

Making some progress... Hot air-ed a connector for GPS Antenna back on. 

Now applying 5V to top of F1 and 12V to what was output of DC-DC converter.

EL302RD Supply now proving 5V @ 230mA and 12V @ 180mA after approx 30 mins

It took a long time for the GPS to do anything but eventually it got an approx location and then after an age it worked out the time; probably not unsurprising due to the ephemeris data being at least 4 years out of date.  It seems to be trying to survey but is having trouble tracking enough satellites.

However, it does not look like I'm all systems go yet..

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

I seem to have a hardware alarm, only time will tell on that one.
 

[Macbeth]

Ah so the XL6009 solution isn't working with the DP832 at all?

No, it won't work at all. The same behavior as the original TI module (which eventually expired). I do wonder if the TI would have worked with my other PSUs? Too late to test that now...

Also regarding DP832 I think I have seen it mentioned in other places that it has been quicker to limit current than some other supplies even if the average current is not yet close to the current limits. So your DP832 may not be behaving differently than other DP832 units. But any other opinions/comments on this are welcome.

Yes kind of strange. Even though the GPSDO only needs <1.7A to run it does have a 10A fuse fitted on board. You do observe up to 8 amp startup spike!

[NivagSwerdna]

I see 500mA at 12V which declines to around 200mA as the OCXO warms up.  That's 6W at start-up, I don't see huge demand above that.

I guess if the onboard TI regulator is dead it makes sense to supply 12V regulated and step-down to 5V  if you have 12V available.

[NivagSwerdna]

By way of keeping myself amused as it does a site survey I have noticed that...

UCCM-P > TIME:STRing?
2016/03/13 12:26:34
Command Complete
UCCM-P >

FWIW Which is 17 seconds ahead of UTC.  So this time is true GPS time and has not been adjusted for the 17 seconds required to make it match wall clock time.  A trap for young players perhaps?   

[PA0PBZ]

I wonder if it is going to correct that:

While most clocks derive their time from Coordinated Universal Time (UTC), the atomic clocks on the satellites are set to GPS time (GPST; see the page of United States Naval Observatory). The difference is that GPS time is not corrected to match the rotation of the Earth, so it does not contain leap seconds or other corrections that are periodically added to UTC. GPS time was set to match UTC in 1980, but has since diverged. The lack of corrections means that GPS time remains at a constant offset with International Atomic Time (TAI) (TAI – GPS = 19 seconds). Periodic corrections are performed to the on-board clocks to keep them synchronized with ground clocks.

The GPS navigation message includes the difference between GPS time and UTC. As of July 2015, GPS time is 17 seconds ahead of UTC because of the leap second added to UTC June 30, 2015. Receivers subtract this offset from GPS time to calculate UTC and specific timezone values. New GPS units may not show the correct UTC time until after receiving the UTC offset message. The GPS-UTC offset field can accommodate 255 leap seconds (eight bits).

https://confluence.qps.nl/display/KBE/UTC+to+GPS+Time+Correction

[uncle_bob]

By way of keeping myself amused as it does a site survey I have noticed that...

UCCM-P > TIME:STRing?
2016/03/13 12:26:34
Command Complete
UCCM-P >

FWIW Which is 17 seconds ahead of UTC.  So this time is true GPS time and has not been adjusted for the 17 seconds required to make it match wall clock time.  A trap for young players perhaps?   

Hi

UTC time has leap seconds in it. GPS time does not have leap seconds. If you have a system (like CDMA) that wants to sync up the codes on every other second ... dropping a second now and then is not a good thing. It is far more common to find systems that run on GPS time than UTC.

Bob

[SHF]

GPS- Display working 

Is there a link you can share to the project.

Here everything is already described.

[NivagSwerdna]

Well it eventually finished its site survey and is now in Position Hold but I don't still don't have any 10Mhz output

UCCM-P > SYSTem:STATus?
-------------------------------------------------------------------------------
090-03861-03   serial number W5609120195   firmware ver 1.0.0.2-01     LINK mode
-------------------------------------------------------------------------------
Reference Status __________________________   Reference Outputs _______________
   Ref 8KHz 0: [LOS]
                                              TFOM     9             FFOM     3
                                              UCCM-P Status[ALARM]

>> GPS: [phase: -2.27e-04]
ACQUISITION ................................................ [ GPS 1PPS Valid ]
Tracking: 5 ____   Not Tracking: 8 ________   Time ____________________________
PRN  El  Az  C/N   PRN  El  Az                GPS      16:38:39     13 MAR 2016
 14  43 295   32     2   8 113                GPS      Synchronized to UTC
 17   8  34   34     6  14  74                ANT DLY  +0.000E+00
 19  30  50   39    10   5 255                Position ________________________
 22   7 322   31    12  85  40                MODE     Hold
 32  -- ---   --    15   8 172
                    24  55 119                LAT      N  51:**:**.***
                    25  54 250                LON      W   0:**:**.***
                    29   6 191                HGT               +11.90 m  (MSL)




ELEV MASK  5 deg
-------------------------------------------------------------------------------
Alarms:  [0200] 0.5Hz Internal Reference
Command Complete
UCCM-P >


Looks that the "[0200] 0.5Hz Internal Reference" alarm suggests something is broken.   

[gm8bjf]

Hi,

I am new to this group and have found the posts very useful, - thanks!. I have just got a Symmetricom GPSDO from a UK supplier on Ebay. It arrived quickly and was in clean (no oil!) condition. A couple of caps were missing or loose but sorted that. Checking the log, it had come from Japan originally. I have been using it with the PUTTY terminal emulator to talk to it, but I have a copy of GPSCon for my Z3801. So far I have had no luck getting GPSCon to talk to the UCCM. Admittedly I have an early version of GPSCon ( Version 1.036 June 2004) but it seems to me as if it should work as they both use SCPI . Has anybody had experience of this ??

Brian.

[Bryan]

Looks that the "[0200] 0.5Hz Internal Reference" alarm suggests something is broken.   

You could try toggling through the following (no particular order) and see what happens. Unlikely that any of the settings write to memory upon power off and I believe the default is active so think your hunch about the internal reference is correct. Problem is trying to diagnose it is difficult as the message is so cryptic. Could be something as simple as a cold solder joint.

OUTPut:ACTive:ENABle
OUTPut:ACTive:DISable
OUTPut:INACTive
OUTPut:INACTive?
OUTPut:STATe?

[NivagSwerdna]

Problem is trying to diagnose it is difficult as the message is so cryptic.

Thanks for the support.  Yeap I'm confused.  Internal to?  The FPGA?  I'm wondering about the components down the edge... L20 was off when I got it.... but I can't see anything obviously out of place.

[uncle_bob]

Problem is trying to diagnose it is difficult as the message is so cryptic.

Thanks for the support.  Yeap I'm confused.  Internal to?  The FPGA?  I'm wondering about the components down the edge... L20 was off when I got it.... but I can't see anything obviously out of place.

Hi

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.

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

Bob

[Bryan]

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.