Hi Ignacio
I'm sure removing the oscillator would make your faultfinding much more
straightforward.
When I removed mine I started out quite convinced I wouldn't be able to do
it, even with the solder mostly removed from around the pins they were
obviously quite a tight fit and all I had available at that time was a plunger
type solder sucker and desoldering braid, as the bits on my old Pace
desoldering kit were well past their best.
The answer basically was lots of braid, lots of patience, and resisting
like crazy any temptation to pull against a hole that wasn't fully released,
but I certainly wouldn't want to do it that way again in a hurry.
The desoldering gun I use now would make it easier but the holes are really
a bit small for those oscillator pins.
The good news though is that the connectors are there as a back up and
fitting them definitely makes it more versatile.
I had considered repeating the performance on another NTGS50AA and/or
NTBW50AA, I really think I should but so far haven't found the courage:-)
I think previous checks for 1PPS outputs might have been limited to the
external connectors but it would make sense if it was available somewhere on
the PCB, I'll try to get one powered up later and check your findings, if I
can find a bit of space that us amongst the usual chaos!
Regards
Nigel
GM8PZR
In a message dated 13/11/2014 01:11:30 GMT Standard Time,
eb4...@cembreros.jazztel.es writes:
Hi Nigel,
Thank you for the suggestions, I was trying to avoid the OCXO removal but
I think that now it must be done.
I was also playing with the idea of populating the connectors so an OCXO
exchange could be easily made, this makes possible to try various
oscillators.
Meanwhile I has been probing and measuring a lot of points and by chance I
found a very interesting thing: Probing TP33 (which is close to the
Trimble chip (U2) and directly connected to pin 76) there is a 1PPS, 10 us wide
signal. I've checked it and appears to be synchronous with the 1/2 PPS
output so maybe it can be routed to an output, probably I'll replace the 1/2
PPS with it, using the existing drive circuit and connector since it is very
straightforward.
My only concern is if this signal only is there during the anomalous
condition that I have now, I have to retest it after fixing it.
I had asked several times if anybody had located a 1PPS signal on these
units, but the responses were negative and I had not probed systematically
the board before. Also I'm taking notes of the signals found and I'll try to
make a partial schematic at least with the EFC circuitry. When I fix it
I'll clean the notes and figures and I'll upload it to some place.
Best regards,
Ignacio
El 12/11/2014 a las 11:47, GandalfG8--- via time-nuts escribió:
Hi Ignacio
I have removed a "faulty" oscillator from one of these, not one of my more
relaxed moments and quite amazed when the board emerged totally undamaged,
but proof at least that it can be done:-)
With the oscillator removed there's access to two sets of connector pads
that will either accept SMA or SMB connectors and after conducting tests
on
the original oscillator via flying leads just soldered to the board I
decided not to fit a replacement to the board after all but to fit a
couple of
SMB connectors to make the setup more versatile, and to avoid the
possibility of having to remove another oscillator in the future:-)
Another advantage of these pads is that if the board does get damaged
removing the oscillator they can still be used as an alternative.
The connectors take the 10MHz from the oscillator into the board and the
EFC control voltage out from the board to the oscillator, now there's a
surprise:-), and oscillator power can be completely external if required.
>From this it would seem that the reference supply from the oscillator
itself is not used in practice, certainly not in the "offboard" case
anyway.
As others have suggested it seems likely your problem may not be the
oscillator itself, but it still might be worth removing anyway to make
testing
and fault finding more straightforward.
The maximum positive excursion of the NTGS50AA should be 6 volts, not 5 as
you're seeing, and another indication it might be worth removing the
oscillator to see how the board behaves stand alone.
I've not seen what seemed to be the repeated attempts at lock that you
mentioned previously, but then I wasn't even aware for a long time that the
control voltage could drive below 3 volts as well as above it:-)
This is my note from previous observation of my "faulty" unit----
-------------------------------------------------------------
When first powered it brings up all LEDs and then switches to a green LED
for a few seconds and then amber. It starts a self survey and acquisition
process with all appearing ok, and the DAC voltage reported as 3.000002
volts.
Sometime later, I've seen as short as 6 minutes but as long as 12 to 15
depending on how long the oscillator has been turned off and allowed to
cool,
once enough satellites are being tracked, the DAC voltage starts to
increase, presumably seeking to drive the oscillator frequency to 10MHz,
but the
frequency doesn't reach 10MHz and the DAC voltage ramps up to 6.000004
volts
over a period of approx 30 seconds where it remains.
As the DAC voltage crosses approx 5.6 volts the Red "fault" LED is
switched on, as opposed to green that would normally be expected to
indicate all
was well, and Lady Heather's "OSC:" report switches from Good to Bad and
highlights red. Similarly "Normal OSC age" changes to "OSC age alarm" and
also
highlights red.
---------------------------------------------------------------
I've attached a Lady H plot that shows this, hopefully it will get through
OK.
The above DAC voltages were as reported by Lady Heather but I've checked
these and, when the board is working as it should be anyway, they're very
close.
In my case the problem described above was an oscillator that had aged
beyond the upper 6 volt limit, needing approx 6.54 volts to reach 10MHz,
and
once removed from the board I was able to add a simple op amp level
shifter
to bring it back into range just to prove all else was ok, which it was,
but obviously Lady H now indicated the EFC into the level shifter rather
than
at the oscillator itself.
Whilst your problem sounds like it might not be quite such an obvious fix,
removing the oscillator would open the loop and make testing both the
oscillator and the board much easier, so much as it's a pain I do feel
that's
probably your best next step.
Regards
Nigel
GM8PZR
In a message dated 12/11/2014 02:06:54 GMT Standard Time,
_eb4apl@cembreros.jazztel.es_ (mailto:eb4...@cembreros.jazztel.es) writes:
Hi,
Removing the oscillator for testing and replacing it with other if it
was the culprit was my first option. I have a spare Trimble oscillator
that probably came from other NTGS50AA since it still have the foam band
attached, but this oscillator is really aged, it needs 7.91 V to bring
it on spot and the maximum control voltage of the NTGS50AA is 5 V.
I was trying to avoid removing the oscillator but probably it must be
done to clarify things.
Thank you,
Ignacio EB4APL
.
El 12/11/2014 a las 2:40, Mark Sims escribió:
I have seen this caused by the oscillator not responding to the EFC
signal. Fixed it by swapping in a MV-89 oscillator.
The oscillators used in these units don't output an oven temperature
monitor signal.
_______________________________________________
time-nuts mailing list -- _time-nuts@febo.com_ (mailto:time-nuts@febo.com)
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- _time-nuts@febo.com_ (mailto:time-nuts@febo.com)
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- _time-nuts@febo.com_ (mailto:time-nuts@febo.com)
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
