Ed,
I nailed it, R7 2M ohm, a crappy old carbon composition resistor had gone high to 3 Meg in the positive feedback loop to the 741. Once replaced The temperature still wasn't hitting 79 degrees I checked all the other resistors and found R12 6K81 was a little low at 6K79 so I went through my metal film boxes and found one that was spot on 6.81K. Replaced that' but still not the right temperature. The only thing left was the thermistor and the 741. The thermistor appeared okay at 18K cold so that left the 741. Luckily, I had some new 741HM metal can jobs in stock. Once it was replaced all is now hunky dory. Temperature is a steady 79 degrees. Multiple component failures are a worry to me, I can explain the 2M resistor but the 741 failing is not good. Also the back of the board is lacquered. When I used my PCB cleaner for clean the solder flux off, it melted the lacquer leaving a sticky white coloured goo on the back of the board. I had to get a tooth brush and scrub it all off and apply a new coat of lacquer. Didn't see that one coming ;) Well I am happy to say that The output isn't sweeping anymore, however its locked to the wrong frequency! The counter I trust implicitly, I have 6 house standards that all read 10 000 000 07 on it so I know exactly what 10 Mhz is on it. For some reason the FRK has locked to 10 000 117 54 and there it stays. According to the troubleshooting flowchart it's the A21 Crystal oscillator board. They mention one should set the trimmer cap to midway and disconnect the wire off E9 and apply +6V there. Form there you have to pick 2 values for 2 caps to set the centre frequency and adjust range (C11 and C12) But with my luck its probably not that easy.. I really should get some sleep... -marki -----Original Message----- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Ed Palmer Sent: Friday, 24 May 2013 5:02 AM To: time-nuts@febo.com Subject: Re: [time-nuts] 9390 GPS RX I applaud your enthusiasm, but Slow Down! Don't go randomly trying things. The more you touch, the more you break! If you damage the Rb lamp, you will not be able to find a replacement. You shouldn't have touched it without a good reason. 1. Did you confirm that the frequency sweep isn't getting to 10 MHz? What are the frequency limits on the sweep? Are you sure about the calibration of your counter? Since you've already adjusted the trimmer you don't know what the values were before, but can you adjust the trimmer so that the sweep includes 10 MHz exactly? If your counter isn't up to the challenge, put your house standard on one channel of your scope and put the FRK output on the other. Trigger off the house standard and if the FRK is centered around 10 MHz you should see the FRK as a blur that eventually slows down so you can see it scrolling left or right, stops, and then starts scrolling the other direction until it's a blur again. If it's just a continuous blur, it isn't reaching 10 MHz, but it's tough to tell whether it's high or low in frequency. Hopefully, your counter can handle that. 2. The temperature shift on the crystal seems high. I don't trust non-contact temperature guns. The emissivity of the target has too much effect on the reading. Do you have a thermocouple or solid-state probe that you can use? Before changing resistors, check for bad solder joints in the temperature sensing circuit and check the transistor that's bolted to the crystal enclosure. Is the bolt snug? It might be worth the effort to carefully remove the bolt, clean off the old heat sink grease, and apply fresh grease. Take special notice of the odd washer under the bolt. It should be cone-shaped and the outside of the cone should be against the transistor. I have one FRK where a similar washer was installed upside-down. The transistor eventually burned out. Maybe coincidence, maybe not. 3. The crystal control voltage should be moving up and down with the frequency, but it should be sweeping from ~ 1 - 12 volts. It can't go negative because there's no negative supply. Check the ground point of your meter. There are other things that need to be checked, but that's enough for now. Ed On 5/23/2013 10:38 AM, Mark C. Stephens wrote: > Okay, I pulled the black box cover off and was greeted by a picture of how > things should be made. After some considerable time staring at the veritable > work of art, I thought I saw the crystal hiding behind the foam. So I gently > removed the foam and marked on the xtal is 79 degrees C. Cool, Well actually > that's hot! So I have powered it up for 30 minutes and measured the > temperature with a very accurate temperature gun I use for measuring > preheating on rework jobs. Huh, its sitting dead on 60 degree's. I think > therein, lies our problem, the crystal never reaches turning point. > According to the fine manual, Increasing R8 lowers the temperature. > Therefore, If I decrease R8 It should theoretically, increase the temperature? > The conundrum is, Shall I just change R8 value or perhaps there is something > else wrong. > What do you think Guys, R8 or something else? > I am not going further without some of the abundant collective wisdom and > experience contained in the time-nuts members! > > > -marki > > -----Original Message----- > From: Mark C. Stephens > Sent: Friday, 24 May 2013 2:01 AM > To: Discussion of precise time and frequency measurement > Subject: RE: [time-nuts] 9390 GPS RX > > Ed, > > > Okay, Lying there I couldn't stop thinking about its lone Ball. > > So I setup the jig, Powered it up and yep, after half an hour the frequency > is doing the up/down swing thing. Interesting, I just happened to come > across that page that reckons you can rejuvenate a lamp with a heat gun. So > I thought, hmm that's easy, let's try that, so I did, and the frequency is > not swinging so quickly now. Could be an symptom, but I think coincidence. > Anyway, next I connected a DVM to the xtal volts output monitor pin as per > the manual. > Uhuh, its swinging in tandem with the frequency swing of the 10 Mhz output > swing. > Gets to 2V and then swings down to -2V Nowhere near the 8V defined in > the manual. > So I tried adjusting the trimmer as per the manual. > Nope won't go above 2V at the fully clockwise limit of the trimmer. > > So that is where I am at. Looks like I will have to pull it apart and fix it > then. > Does it sound/look like the crystal has gone out of adjustable range? > > > -marki > > > -----Original Message----- > From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] > On Behalf Of Mark C. Stephens > Sent: Friday, 24 May 2013 12:22 AM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] 9390 GPS RX > > Hey Ed, Well I have its Ball (just one? ;) Efratom out on the bench. > > Seems they built this stuff to service, huh? Nice. > > I managed to make a mating connector out of 2.54mm pitch header strip as per > your suggestion. > Whew, that was my biggest concern! > > Anyway, its after midnight and I have a full day ahead, Looking forward to > getting this old gal working again. > I can't help giving the 9390 a reassuring pat every time I walk past it ;) > its sitting there merrily running off the house standard although PDOP hasn't > gone below 4 which has me a tad worried. > It seems, I have become quite attached to this 9390 :p > > > -marki > > > -----Original Message----- > From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] > On Behalf Of Ed Palmer > Sent: Thursday, 23 May 2013 1:16 AM > To: time-nuts@febo.com > Subject: Re: [time-nuts] 9390 GPS RX > > > On 5/22/2013 4:58 AM, Mark C. Stephens wrote: >> It's a 9390-55024 >> >> I have plugged my counter into the Efratom rubidium oscillator thing and >> disconnected the EFC. >> >> It is actually wobbling ~ +/-650Hz, peaking as much as +/- 1KHz. >> So, hazarding a guess, something is very wrong inside the black box thing. > Is it really wobbling around randomly, or is it sweeping up and down. > Your counter could be fooling you by taking 'snapshots' at intervals > dependent on the gate time setting. If the frequency is wobbling randomly > that would likely mean an actual fault in the FRK rather than something that > needs adjusting. If it's sweeping up and down, that means that it's > searching for the rubidium signal, but not finding it. > Every rubidium will do that, but it should find the signal within 5 - 10 > minutes. That could mean an adjustment or a fault depending on the actual > frequency range that it's sweeping over. Obviously, you want the frequency > range to be 10 MHz +- something. > >> My biggest fear is, wherever will I get the 'Winchester' connector used on >> this oscillator? > That's easy. Improvise! Go into your box of junk connectors and find a > female connector that uses pins of approximately the same diameter. > Remove the sockets from the connector body, solder wires onto them, insulate > them with tape or heat shrink and slide them over the pins on the FRK > connector. For example, RS-232 sockets are a bit big, but could be squashed > down. Floppy disk connectors are usually really easy to remove from the > body. I'm not sure if they'd work, but you get the idea. It doesn't have to > be neat or elegant. It's just temporary for a test. > > Ed > >> What I mean is, for a proper bench job, according to the manual, I'd have to >> remove the whole rubidium from the 9390 and put it on the clean bench for >> disassembly. >> Then I can connect various voltmeters to monitor the various signals, and if >> needed, replace parts and re-align. >> However, I am unwilling to lop off the connector in the 9390, to only have >> to put it back on/in after Mr. Balls Efratom is back to normal. >> >> The other way, I suppose is to bodge up wires from the inside of the >> connector to some sort of temporary Jig for the service job. >> >> Reading the Most Interesting FRK.PDF, it sounds like the crystal oscillator >> assembly has issues, whether the crystal oven is broken or similar. >> That is a really interesting document, worth the read, even just for >> the heck of it ;) >> >> -marki >> _______________________________________________ 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.
