[time-nuts] 9390 GPS RX

Mark C. Stephens marks at non-stop.com.au
Wed May 22 06:58:08 EDT 2013

It's a 9390-55024

I have plugged my counter into the Efratom rubidium oscillator thing and disconnected the EFC.

It is actually wobbling ~ +/-650Hz, peaking as much as +/- 1KHz.
So, hazarding a guess, something is very wrong inside the black box thing.

My biggest fear is, wherever will I get the 'Winchester' connector used on this oscillator?

What I mean is, for a proper bench job, according to the manual, I'd have to remove the whole rubidium from the 9390 and put it on the clean bench for disassembly.
Then I can connect various voltmeters to monitor the various signals, and if needed, replace parts and re-align.
However, I am unwilling to lop off the connector in the 9390, to only have to put it back on/in after Mr. Balls Efratom is back to normal.

The other way, I suppose is to bodge up wires from the inside of the connector to some sort of temporary Jig for the service job.

Reading the Most Interesting FRK.PDF, it sounds like the crystal oscillator assembly has issues, whether the crystal oven is broken or similar.
That is a really interesting document, worth the read, even just for the heck of it ;)


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Rob Kimberley
Sent: Wednesday, 22 May 2013 7:16 PM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] 9390 GPS RX


What is the full model number (from label on rear)? It will be 9390-xxxx.  


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Mark C. Stephens
Sent: 22 May 2013 07:56
To: time-nuts at febo.com
Subject: Re: [time-nuts] 9390 GPS RX

Just a Follow up,

I checked the 10 Mhz output of the 9390 and it was... ~12 MHz.
Uhuh, Wiggling some cables I came across one that when pressure was put on it, the frequency dropped back to 10Mhz.
The was J9 on the main (logic?) board.

Now I need to mention this particular 9390 has a separate board for the
16.368 oscillator.
>From the photo's I posted earlier, it is the 2nd card in from the front on the right.
>From earlier posts I have gathered this is normally present on the Trimble GPS monstrosity.
My Point is, this particular 9390 isn't your average model.

With the frequency now at 10 Mhz I tried a number of different antennae / terminator combinations and eventually I was able to find a satellite.
Just 1? And it dropped in and out all the time.

Watching the 10 Mhz, it was drifting  +/- 500Hz.

That definitely wouldn't do, so I plugged the house standard into the
(external) time base input and the 9390 10 Mhz output became stable.
After a few minutes, I had 2 satellites! Cool.. 5 minutes we had 4 birds and we are doing "GPS Correction"

Being the inquisitive sort I went in reverse, unplugging the house standard from the (external) time base input.
Uhuh, we are back to 1 satellite dropping in and out. The GPS receiver definitely doesn't like the 10MHz reference wobbling about all over the place like a drunk sailor on shore leave..

Of course I plugged the House standard back in and we are in business again with 4 Satellites, locked and loading.
No drop outs either. Interesting.

So My question is, (mostly to myself) Is the Efratom FRK Faulty and the root of the Drift?
And how do I fix it, I ask myself?

I have downloaded the FRK manual for perusal, I believe there is an external adjustment to bring it into lock area.
It may also be a problem with the PLL loop, fun stuff because I don't have a schematic.

You see, the service manual I was supplied with when I purchased the 9390 isn't for this unit.
It's for the much newer varieties.
There is no mention of this particular Trimble GPS receiver with its multiple sub-boards nor mention of a FRK oscillator in it.

I did a search of earlier time nuts posts and found there are quite a few time nuts with 9390's, although there appear to be drastic differences between the different 9390's.
Perhaps I should be going on the postfix, for instance mine is a 9390-55024.

Bah, I just noticed the GPS day is wrong, I think we are ~142 but its saying 278, Is that a GPS receiver bug?

So, Any helpful navigation hints before I embark on this Journey?

Many thanks,

From: Mark C. Stephens
Sent: Tuesday, 21 May 2013 8:42 PM
To: 'time-nuts at febo.com'
Subject: 9390 GPS RX

Hello Fellow time nuts,

I received a Datum 9390 GPS receiver I bought off eBay today. It had a PSU fault and I am running it off a bench supply until I can get the PSU working again. All the PSU does is supplies 28V so I can probably adopt a more recent supply to fit if I can't fix the old one. I pulled the PSU apart and so far found a blown triac. There is bound to be more 'things' blown but I want to see if it's worth repairing first. I mean, it's not much use repairing something that proves to be useless?

Funnily enough in the back of the Manual binder was a second manual. A service Manual for a Trimble 5000A GPS/TIME frequency monitor. I'll scan it if anyone needs it?

This particular 9390 is an odd Chap, doesn't look at all like picture in the supplied manual.

When I opened it up,
http://www.vk2hmc.net/blog/wp-content/uploads/2013/05/9390-insides.jpg  I saw an Efratom FRK!

I am having a bit of problem identifying the GPS module. It says Trimble navigation on the board:
I measured the antenna Jack for the expected 15V normally on a Datum 9390, but found it was 5.1 volts.
I could not get rid of the Antenna feed error until I put a 50 ohm terminator on it. I tried higher values (75-180R) but the only value that cleared the feed error was 50 ohms. So I used a BNC 'tee' and terminated the output of the GPS distribution amp to the 9390. I fear this GPS RX requires an antenna with a down-convertor -or- a whacking great L1 signal. I always thought the 9390 had a Trimble svee6 module in them. But this one's positively ancient.
I have entered my approximate co-ordinates to see if it finds any birds but so far no luck.

If you know anything about this GPS board, please leave me a message?

The interface convertor from the Trimble to the Datum:
http://www.vk2hmc.net/blog/wp-content/uploads/2013/05/gps-bd-if.jpg is labelled "Datum TANS interface".


Complete blog post is here: http://www.vk2hmc.net/blog/?p=178

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