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.
