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

[ekyle]

I've made a very nice discovery this evening. I know there have been several questions posted about a battery backup for the GPS data. Well, I was looking at the silk screen printing for J3. It reads 1:Rx, 2:Tx,3:BT,4:GD. 1,2 are of course the serial port. 4 is ground. BT.... Could it be short for battery? While the unit was on I measured about 3.2v on pin 3. I hooked up a power supply to pin3 and removed power on the unit. I waited a while and plugged it back in. It booted and I could see immediately that it had the GPS location and was in hold mode. Now for the bad news. With the unit powered off, it draws about 88ma from this pin and 0ma when its on. It could be that it keeps the GPS receiver alive with it. Definitely not just a CMOS memory backup. I'm not sure if its current limited so a super cap could be used on it.

[Bryan]

Thanks for sharing the find. 88ma is a far amount for backupt, but would be ok for a short disconnect, like moving the unit or a brief power outage. I assume that there is protection circuitry built in and it is safe to just connect a 3.3v supply to it.

[NivagSwerdna]

re: Battery
https://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/msg896521/#msg896521
and
https://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/msg896506/#msg896506
From my experience you can reach PLL stability very rapidly by setting Hold position (assuming you know it from a previous survey)

[Bryan]

From my experience you can reach PLL stability very rapidly by setting Hold position (assuming you know it from a previous survey)

A method for quickly loading in the last known location.

https://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/msg890574/#msg890574

[ekyle]

Thanks for sharing the find. 88ma is a far amount for backupt, but would be ok for a short disconnect, like moving the unit or a brief power outage. I assume that there is protection circuitry built in and it is safe to just connect a 3.3v supply to it.

I didn't see any current draw when I connected a power source of 3.2v. One might be able to use a super cap with a resistor to charge it and then a Schottky diode in parallel with the resistor with the cathode pointing to the input pin for the discharge path.

[Vgkid]

Has anyone determined the leaning of the flashing led's. I always have a green 1pps(sort of close), a faster flashing green led. Unfortunstrly that one was replaced by a flashing red led after a few days.

[rastro]

Problems getting board to lock into 10MHz GPS. 

History:
1. L20 was lifted so replaced with ~ 5uH SMD inductor
2. 12V power was loading down 5V supply and squealing - removed DC/DC daughter board and using separate 5V and 12V supplies.

What appears good:
1. Boots up and can communicate through 4-pin RS232 connector.
2. Completes site survey
3. Has 10MHz at output of OSC close to 10MHz.
4. Has output at 1PPS MCX connector.

Problem symptoms:
1. Will not feed through 10MHz clock after successful site survey.  Can force 10MHz output at MCX connector by toggling MACI button on PCB.
2. LED:GPSLock = 0  which probably means the system is not attempting to output the 10MHz clock.
3. OUTPut:STATe = UNLOCK and SYNChronization:FFOMerit = PLL unlocked ; Indicates problem with PPL for the 10MHz OSC
4. status shows #H/W FAIL ---------- [ LINK ] and #OPERATION ALARM --- [ EFC ],  Not sure what LINK is.  EFC possible "Electronic Frequency Correction"?
5. ALARm:HARDware? = NONE;  After all this I would think there would be a hardware alarm !!??
6. Tried changing "satellite elevation mask" (GPS:SAT:TRAC:EMAN) to different values but made no effect.

So it appears the PLL is failing is related to EFC.  Is there some hidden setup I'm missing?  Any signals to check?

Code: [Select]

UCCM-P > SYST:STAT?
-------------------------------------------------------------------------------
090-03861-03   serial number W*********   firmware ver 1.0.0.2-01     LINK mode
-------------------------------------------------------------------------------
Reference Status __________________________   Reference Outputs _______________
XX Ref 8KHz 0: [LOS]                         
                                              TFOM     9             FFOM     3
                                              UCCM-P Status[OCXO WARM]
                                             
>> GPS: [phase: -1.96e-06, adjusting freq]   
ACQUISITION ................................................ [ GPS 1PPS Valid ]
Tracking: 5 ____   Not Tracking: 6 ________   Time ____________________________
PRN  El  Az  C/N   PRN  El  Az                GPS      12:15:21     06 JUN 2016
  1  23 253   33    10   7 147                GPS      Synchronized to UTC
  3  38 313   34    22  62 292                ANT DLY  +0.000E+00
 14  36  75   38    23  11 293                Position ________________________
 16  23 176   31    25  11  38                MODE     Hold
 32  29  85   43    26  47 151               
                    31  60  27                LAT      N  **:**:**.***
                                              LON      W  **:**:**.***
                                              HGT              +***.** m  (MSL)
                                             
                                             
                                             
                                             
ELEV MASK 10 deg                             
-------------------------------------------------------------------------------

UCCM-P > status

                 - UCCM Slot STATE -



1-1. #Now ACTIVE STATUS ---------------- [OCXO Warm]
1-2. #Before ACTIVE STATUS ------------- [Wait for GPS]
2-1. #Reference Clock Operation -------- [Not Used]
2-2. #Current Reference Type ----------- [GPS]
2-3. #Current Select Reference --------- [GPS 1PPS]
2-4. #Current Reference Status --------- [Ref Analyzing]
     #GPS STATUS ----------------------- [Available]
     #Priority Level ------------------- [GPS > LINK]
     #ALARM STATUS
     #H/W FAIL ---------- [ LINK ]
     #OPERATION ALARM --- [ EFC ]
3-1. PLL STATUS ------------------------ [Enable]
3-2. Current: PLL MODE ----------------- [OFFSET OBSERVATION MODE]
Command Complete

UCCM-P > OUTPut:STATe?
UNLOCK
Command Complete

UCCM-P > LED:GPSLock?
0
Command Complete

UCCM-P > ALARm:HARDware?
NONE
Command Complete

UCCM-P > SYNChronization:FFOMerit?
PLL unlocked
Command Complete

UCCM-P > SYNChronization:TFOMerit?
Greater than 1E8 ns
Command Complete


[PA0PBZ]

1. L20 was lifted so replaced with ~ 5uH SMD inductor

Are you sure that L20 is a single inductor?

Edit: Just took one of a pcb and there is continuity both at the upper part ( R105) and the lower part, so it looks like there are 2 coils.
Even after taking off L20 there is still continuity on the lower part, but maybe it needs the coil?

[davebb]

Hi is that inductor connected in any way to the crystal? if so you will need the exact value as the wrong value will change the resonant circuit frequency ?
Dave Browne 2E0DMB

[PA0PBZ]

Hi is that inductor connected in any way to the crystal? if so you will need the exact value as the wrong value will change the resonant circuit frequency ?
Dave Browne 2E0DMB

It looks like the crystal is directly connected to the LSI on the bottom, but I just found that the upper right of L20 (where the 5 from R105 is) goes directly to the RF output of the TXCO.

[Bryan]

4. status shows #H/W FAIL ---------- [ LINK ] and #OPERATION ALARM --- [ EFC ],  Not sure what LINK i

I believe the H/WFAIL --- is normal, just means it is not sensing another unit. Think they were designed by the mfg to work with another, possible redundancy backup in the field I assume.

Your TFOM is way out, I note just under this statement it shows UCCM-P Status[OXCO warm], mine shows UCCM-P Status[ACTIVE] or UCCM-P Status[HOLDOVER] if it loses sight of enough birds or a antenna disconnect. Are you sure the unit is fully warmed up?

[rastro]

4. status shows #H/W FAIL ---------- [ LINK ] and #OPERATION ALARM --- [ EFC ],  Not sure what LINK i

I believe the H/WFAIL --- is normal, just means it is not sensing another unit. Think they were designed by the mfg to work with another, possible redundancy backup in the field I assume.

Your TFOM is way out, I note just under this statement it shows UCCM-P Status[OXCO warm], mine shows UCCM-P Status[ACTIVE] or UCCM-P Status[HOLDOVER] if it loses sight of enough birds or a antenna disconnect. Are you sure the unit is fully warmed up?

What kind of values should I expect for a valid TFQM?
I think the OSC is warmed up - it's very hot to the touch. 
- If I measure its temperature what should I expect? 
- Is there status command I can use to see the OSC status?
- Also the 12V supply starts at about 500mA when cold then kicks down to lower current after several minutes.  It would appear the oven is regulating.  However I don't know what or how the systems controller makes a determination on when the oven temp is regulated at an working level.

I may try and kluge back on the L20 as some have suggested - I don't think it's gonna be easy because it has very fine wires. 
Has anyone successfully replaced L20 and have a working system i.e. PPL working?

-rastro

[PA0PBZ]

Ok, I just managed to measure L20 by sticking it on my bench with double sided tape 
Both coils (upper and lower) measure 5uH, there's no connection between the 2 coils.

5uH ]|[ 5 uH

So either they used a left-over component in there or you will not get away with a single coil. The fact that one of the upper legs is connected to the RF output of the TCXO makes me believe that it is used to couple part of the output to the PLL? That would certainly explain why it doesn't lock with a single coil...

[ekyle]

Problems getting board to lock into 10MHz GPS. 

History:
1. L20 was lifted so replaced with ~ 5uH SMD inductor
2. 12V power was loading down 5V supply and squealing - removed DC/DC daughter board and using separate 5V and 12V supplies.

What appears good:
1. Boots up and can communicate through 4-pin RS232 connector.
2. Completes site survey
3. Has 10MHz at output of OSC close to 10MHz.
4. Has output at 1PPS MCX connector.

Problem symptoms:
1. Will not feed through 10MHz clock after successful site survey.  Can force 10MHz output at MCX connector by toggling MACI button on PCB.
2. LED:GPSLock = 0  which probably means the system is not attempting to output the 10MHz clock.
3. OUTPut:STATe = UNLOCK and SYNChronization:FFOMerit = PLL unlocked ; Indicates problem with PPL for the 10MHz OSC
4. status shows #H/W FAIL ---------- [ LINK ] and #OPERATION ALARM --- [ EFC ],  Not sure what LINK is.  EFC possible "Electronic Frequency Correction"?
5. ALARm:HARDware? = NONE;  After all this I would think there would be a hardware alarm !!??
6. Tried changing "satellite elevation mask" (GPS:SAT:TRAC:EMAN) to different values but made no effect.

So it appears the PLL is failing is related to EFC.  Is there some hidden setup I'm missing?  Any signals to check?

Code: [Select]

UCCM-P > SYST:STAT?
-------------------------------------------------------------------------------
090-03861-03   serial number W*********   firmware ver 1.0.0.2-01     LINK mode
-------------------------------------------------------------------------------
Reference Status __________________________   Reference Outputs _______________
XX Ref 8KHz 0: [LOS]                         
                                              TFOM     9             FFOM     3
                                              UCCM-P Status[OCXO WARM]
                                             
>> GPS: [phase: -1.96e-06, adjusting freq]   
ACQUISITION ................................................ [ GPS 1PPS Valid ]
Tracking: 5 ____   Not Tracking: 6 ________   Time ____________________________
PRN  El  Az  C/N   PRN  El  Az                GPS      12:15:21     06 JUN 2016
  1  23 253   33    10   7 147                GPS      Synchronized to UTC
  3  38 313   34    22  62 292                ANT DLY  +0.000E+00
 14  36  75   38    23  11 293                Position ________________________
 16  23 176   31    25  11  38                MODE     Hold
 32  29  85   43    26  47 151               
                    31  60  27                LAT      N  **:**:**.***
                                              LON      W  **:**:**.***
                                              HGT              +***.** m  (MSL)
                                             
                                             
                                             
                                             
ELEV MASK 10 deg                             
-------------------------------------------------------------------------------

UCCM-P > status

                 - UCCM Slot STATE -



1-1. #Now ACTIVE STATUS ---------------- [OCXO Warm]
1-2. #Before ACTIVE STATUS ------------- [Wait for GPS]
2-1. #Reference Clock Operation -------- [Not Used]
2-2. #Current Reference Type ----------- [GPS]
2-3. #Current Select Reference --------- [GPS 1PPS]
2-4. #Current Reference Status --------- [Ref Analyzing]
     #GPS STATUS ----------------------- [Available]
     #Priority Level ------------------- [GPS > LINK]
     #ALARM STATUS
     #H/W FAIL ---------- [ LINK ]
     #OPERATION ALARM --- [ EFC ]
3-1. PLL STATUS ------------------------ [Enable]
3-2. Current: PLL MODE ----------------- [OFFSET OBSERVATION MODE]
Command Complete

UCCM-P > OUTPut:STATe?
UNLOCK
Command Complete

UCCM-P > LED:GPSLock?
0
Command Complete

UCCM-P > ALARm:HARDware?
NONE
Command Complete

UCCM-P > SYNChronization:FFOMerit?
PLL unlocked
Command Complete

UCCM-P > SYNChronization:TFOMerit?
Greater than 1E8 ns
Command Complete


Check the output of the diagnostic log: DIAGnostic:LOG:READ:ALL?
It might tell you if the EFC is at the limits or if the OCXO current is too high/low. You can also measure the EFC voltage on the OCXO. Its the middle pin on the side that has 3 pins. Mine was about 2.7v when working and pegged at 5.1v when my OCXO was acting up. If the EFC voltage is towards the low end, the OCXO may be too warm. e.g. The temperature controller inside the OCXO failing.

[rastro]

Check the output of the diagnostic log: DIAGnostic:LOG:READ:ALL?
It might tell you if the EFC is at the limits or if the OCXO current is too high/low. You can also measure the EFC voltage on the OCXO. Its the middle pin on the side that has 3 pins. Mine was about 2.7v when working and pegged at 5.1v when my OCXO was acting up. If the EFC voltage is towards the low end, the OCXO may be too warm. e.g. The temperature controller inside the OCXO failing.

Good idea:
Ran diagnostic log:  Most lines are "Time set to GPS" but did see EFC related error.
...Time set to GPS
.
.
L336:2016-06-07 20:52:08:Near EFC Sat Alarm : 0%  #appears to be when alarm gets set some time into the site survey.
...Time set to GPS
L366:2016-06-07 21:13:22:Position hold mode started ... #this is probably OK I think this occurs at completion of site survey - my guess.

Also thanks for pointing out where I can measure the EFC voltage.  I'll have to monitor it.

PA0PBZ,
I'm also starting to believe that this L20 may be more of a transformer than just a simple coil/inductor.  I tried to fix and remount the original L20 but I could not solder the loose wires that go on the pads nearest the PCB edge.  I ended up soldering the half that was still attached to L20 pads that go close to the OCS and for the pads near the PCB edge I soldered a small loop of wire.  I really did not have much to work with.  Anyway it still got the same failure. 

So before trying to figure out a new L20 solution I will look at the EFC voltage - perhaps that will provide further insight.

-rastro

[rastro]

hi to all,
received my Symmetricom board yesterday. As to be exspected some damage could be seen. On the top side xtal y1 is missing, inductor L20 was ripped off. On the botton side capacitor C26 and resistor R83 were missing.
R83 could be easily identified as 103 (10kOhm), C26 is in neighbourhood of C27 which I measured as 1.2 uF. I put in 0.56 uF as a provisory measure.
Inductor L20 I measured as 5uH and replaced with a new one. Since xtal Y1 is missing, I suggested it to be 22.118.400 Hz. Is there any kind soul able to confirm this value?
Unit seems to be working fine when injecting 22118400 Hz from an external generator.
regards Goetz

Hello Goetz;
I tried doing something similar to repair my boards damaged L20 but still have problems - perhaps I have additional issues.  I want to verify your solution worked 100% for you.
You replaced L20 with an inductor ~ 5uH. 
1. What type did you use (coil/SMD?)??
2. This was mounted near R105(unpopulated) between the 2 pads nearest the OSC.
3. Did you leave the 2 pads nearest the PCB empty?  L20 has 4 pads.
4. Could you confirm that the board completes the site survey and gets phase lock.  So that LED:GPSLock? = 1 .

Thanks
-rastro

[Bryan]

4. status shows #H/W FAIL ---------- [ LINK ] and #OPERATION ALARM --- [ EFC ],  Not sure what LINK i

I believe the H/WFAIL --- is normal, just means it is not sensing another unit. Think they were designed by the mfg to work with another, possible redundancy backup in the field I assume.

Your TFOM is way out, I note just under this statement it shows UCCM-P Status[OXCO warm], mine shows UCCM-P Status[ACTIVE] or UCCM-P Status[HOLDOVER] if it loses sight of enough birds or a antenna disconnect. Are you sure the unit is fully warmed up?

What kind of values should I expect for a valid TFQM?
I think the OSC is warmed up - it's very hot to the touch. 
- If I measure its temperature what should I expect? 
- Is there status command I can use to see the OSC status?
- Also the 12V supply starts at about 500mA when cold then kicks down to lower current after several minutes.  It would appear the oven is regulating.  However I don't know what or how the systems controller makes a determination on when the oven temp is regulated at an working level.

I may try and kluge back on the L20 as some have suggested - I don't think it's gonna be easy because it has very fine wires. 
Has anyone successfully replaced L20 and have a working system i.e. PPL working?

-rastro

As ekyle mentioned it may not be that the OCXO needs warming up but that the EFC voltage is out of range . You want FFOM at 0 and the lowest possible number for TFOM. Personally I have never seen below 2 due to I think limited visibility of satellites. Would be interested if others have seen a TOFM <2.

TFOM (Time Figure of Merit) is the accuracy of the 1 PPS signal, with 0 < 1ns, 1= 1 to 10 ns, 2 = 10 to 100 ns, 3 = 100ns to 1us, ... 9 > 1ms
FFOM (Frequency Figure of Merit) is the stability of the 10MHz signal. 0 = PLL stable, 1 = stabilizing, 2 = holdover, 3 = unlocked (do not use as 10MHz out of spec)

[kutte]

Hello Goetz;
I tried doing something similar to repair my boards damaged L20 but still have problems - perhaps I have additional issues.  I want to verify your solution worked 100% for you.
You replaced L20 with an inductor ~ 5uH. 
1. What type did you use (coil/SMD?)??
2. This was mounted near R105(unpopulated) between the 2 pads nearest the OSC.
3. Did you leave the 2 pads nearest the PCB empty?  L20 has 4 pads.
4. Could you confirm that the board completes the site survey and gets phase lock.  So that LED:GPSLock? = 1 .

Thanks
-rastro

hi rastro,
1 . for L20 I used an smd choke 4x4.5 mm 2.2 uH 2.5 A
2 & 3 both yes, I looked at my ripped off L20 and did find only one coil.  L20 is mounted in parallel next to the unpopulated R105
4 yes, my board does run fine (with two green blinking LEDs) and all status messages ok as you can see from my other postings in this thread.
hope this helps Kutte

[BFX]

New member  Waiting for antenna and additional cables:)

[NivagSwerdna]

New member  Waiting for antenna and additional cables:)

Welcome.  Your board looks in good condition.  I can see one small SMD cap floating in the bag!  Don't lose it!

[BFX]

New member  Waiting for antenna and additional cables:)

Welcome.  Your board looks in good condition.  I can see one small SMD cap floating in the bag!  Don't lose it!

Thx I will make better photos. I know it is C27. I think it's passed out during transportation, also one corner of PCB is a little damaged.
I should check whole pcb for cold joints or any damages by microscope.

[NivagSwerdna]

I got my simple 1 in 4 out 10MHz distribution working. The RF transformers are probably overkill but I found them at eBay auction: #251401324712 and could not resist.
Schematic attached and bare PCB at cost if anyone else is interested.

[Bryan]

I see the seller of the Symmetricom boards has just recently swapped out the pictures to the Trimble 57963. Ran out and selling the Trimble?

http://www.ebay.com/itm/331805445560?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

[grumpydoc]

I see the seller of the Symmetricom boards has just recently swapped out the pictures to the Trimble 57963. Ran out and selling the Trimble?

http://www.ebay.com/itm/331805445560?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Probably - I bought a couple but won't have time to play with them for a while

[gm8bjf]

I just bought one of the Trimbles advertised as Symmetricom units from waikeionline_uk and on testing it will not lock up. The only visible damage was a missing 0 Ohm link which I replaced and that did not cure the problem. The SYST:STAT? page shows the OCXO as warming up after many hours of operation and the LEDs never settle into the fast green flashing mode. Bit stumped with this one. I have asked for a refund or a replacement.

Brian.