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, Marki From: Mark C. Stephens Sent: Tuesday, 21 May 2013 8:42 PM To: 'time-nuts@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. http://www.vk2hmc.net/blog/wp-content/uploads/2013/05/9390-fr.jpg When I opened it up, http://www.vk2hmc.net/blog/wp-content/uploads/2013/05/9390-insides.jpg I saw an Efratom FRK! http://www.vk2hmc.net/blog/wp-content/uploads/2013/05/frk.jpg I am having a bit of problem identifying the GPS module. It says Trimble navigation on the board: http://www.vk2hmc.net/blog/wp-content/uploads/2013/05/gps-bd.jpg 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". Marki Complete blog post is here: http://www.vk2hmc.net/blog/?p=178 _______________________________________________ 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.