[time-nuts] 9390 GPS RX

Mark C. Stephens marks at non-stop.com.au
Sat Jun 1 13:54:33 EDT 2013


Ed, I am sure it will be back to haunt us as soon as I clear down the backlog of stuff waiting to get on the workbench :)
The problem with the GPS RX is its upside down on the main system board platform.

It can't be reached unless everything is unplugged and the platform turned upside down.

The person who worked on it previously tried and ended up making all the DIP ribbon cables and a SMB cable intermittent.
I have since replaced them.

My, how time flies when you are having fun though, doesn't it :)


-marki


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Ed Palmer
Sent: Sunday, 2 June 2013 3:36 AM
To: time-nuts at febo.com
Subject: Re: [time-nuts] 9390 GPS RX


On 6/1/2013 9:47 AM, Mark C. Stephens wrote:
> Yep, Phase plot is like a Saw tooth.

So, despite the 'lock' LED, it isn't locked.  Well, maybe something's locked, but we're not sure what.

> I plugged the house standard as external reference (I am sure I did that already) and it still drifts so there is something wrong there somewhere.
> I also measured the DAC voltage going to the FRK and it's not moving from 0.95 volt.
>
> Without schematics I am pretty much stuck at this point.
> I doubt if the Schematic for that RX was ever released.

I'd take a shot at reverse engineering the connections to the receiver.  
See if you can talk to it or, at least, see if the 1 PPS coming out of it is actually locked to GPS.  Maybe that's what the 'locked' LED means.

> BTW, there are ~120Hz varying on those 1st 2 SMB connectors The first 
> is Sine, the second is square.

That's the two that go to the OCXO?  You'd have to trace out the OCXO board to see if that made sense.  I would have expected to see a sine wave output from the board and an EFC DC voltage input. 16.618 MHz could be divided down to 125 Hz which might be used as a reference for phase comparison.  120 Hz would work if the crystal was 16.617 960 MHz.  Now that I think of it, that OCXO should be checked to see to see how far it's drifted over the years.  Whether it's supposed to be phase-locked or free-running it could have drifted out of range.

> So, Plan is to Shelve it, on the off chance someone needs bits or I find a parts donor.
> Bit disappointed really, good looking piece of kit.
>
> I have about 1100 other projects on at the moment and they are all falling behind..

Yeah, I know what you mean.  My problem is, I'm too stubborn to give up on a project.  My project list and workbench suffer from the backlog.  
Oh well, it's been fun.  Of couse, you now have a working FRK so the project wasn't a total loss.

Ed

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