Hi It seems reasonable that there is a 1 pps somewhere on the board. The big question is if it’s the output of the GPS receiver or the output of the OCXO after division.
Bob > On Nov 12, 2014, at 8:10 PM, EB4APL <eb4...@cembreros.jazztel.es> wrote: > > 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, >> 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 >>> 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. >> >> >> _______________________________________________ >> 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. > > _______________________________________________ > 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. _______________________________________________ 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.