Bruce, I re-soldered all connections on the 'Output Board' tonight with no improvement. I'll move on to other efforts this weekend.
Joe -----Original Message----- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Bruce Griffiths Sent: Thursday, May 28, 2009 7:13 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Broken Ovenaire OSC 85-50 Joe Whilst its easy enough to construct a miniature RF current probe using a small ferrite core which is slipped over the wire in which the current is to be measured, constructing one using a split ferrite toroid is more difficult as such toroids are difficult to come by. In principle one can construct ones own by cutting and grinding a pair of toroids. Unless one has access to diamond lapping equipment and diamond saws this is probably impractical. Thus you will probably have to revert to measuring the RF voltage across resistors in the circuit to get some idea of the RF current. Bruce J. L. Trantham wrote: > Bruce, > > Simple enough suggestion. > > Replacement transistors should arrive before the weekend. I will try to > replace the transistors and re-solder all the connections. > > I do not have a current probe but I do have an oscilloscope or two. Any > suggestions of a current probe small enough to get into those small spaces? > > Joe > > > > -----Original Message----- > From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On > Behalf Of Bruce Griffiths > Sent: Thursday, May 28, 2009 12:13 AM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Broken Ovenaire OSC 85-50 > > Joe > > In box is fine, 6MB is relatively small and not a problem. > The brown caps look like they might be silver mica. > It may be worth resoldering all the solder joints on these caps as they > can sometimes go high impedance over time. > > The ceramic caps marked 103 are 10,000pF = 10nF = 0.01uF. > > If you have a current probe and oscilloscope it would be useful to look > at the RF current flowing in the crystal, oscillator transistor etc. > > Bruce > > J. L. Trantham wrote: > >> Bruce, >> >> I sent you two pictures directly. I hope I did not choke your inbox. >> > They > >> were a total of about 6 MB. >> >> If so, I can probably reduce the quality and get a smaller file. >> >> Joe >> >> -----Original Message----- >> From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On >> Behalf Of Bruce Griffiths >> Sent: Wednesday, May 27, 2009 11:03 PM >> To: Discussion of precise time and frequency measurement >> Subject: Re: [time-nuts] Broken Ovenaire OSC 85-50 >> >> Joe >> >> Low output can be caused by a high impedance path, an open circuit >> component, an open solder joint, a low value cap, low gain transistor, >> > etc. > >> The oscillator limits by either saturating or better cutting off the >> oscillator transistor (would need to check to see which but its more >> likely to be the latter). >> If oscillator transistor cutoff is the limiting mechanism then too low >> transistor collector current could be one cause. >> >> >> Bruce >> >> J. L. Trantham wrote: >> >> >>> Bruce, >>> >>> Thanks for your analysis. Is this all in your head or do you use a >>> >>> >> computer >> >> >>> program? >>> >>> >>> >>> >> Both. >> I used LTSpice to check. >> >> >> >>> If I understand correctly, you are using the term 'buffer' to describe >>> >>> >> what >> >> >>> I call the 'Output Board'. >>> >>> >> Yes. >> >> >>> If so, then the Output Board seems to be doing >>> what it is supposed to do and the problem is a low output from the >>> Oscillator Board. Any thoughts as to the cause of the low output? >>> Capacitors changing value, resistors changing value, inductors changing >>> value (by the way, I need a refresher on how to read the color code of >>> inductors), transistors loosing gain? I have not measured the >>> > temperature > >>> but the crystal has '79 C' written on it. The capacitors appear to be >>> dipped silvered mica and the resistors appear to be carbon. >>> >>> I can send a picture of both boards if that would help. >>> >>> >>> >>> >> Yes that may help. >> >> >> >>> Joe >>> >>> -----Original Message----- >>> From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On >>> Behalf Of Bruce Griffiths >>> Sent: Tuesday, May 26, 2009 10:43 PM >>> To: Discussion of precise time and frequency measurement >>> Subject: Re: [time-nuts] Broken Ovenaire OSC 85-50 >>> >>> Joe >>> >>> A quick analysis if the buffer indicates that the gain with a 50 ohm >>> load is about 1x. >>> The gain into a 1M load should be about 4x. >>> Simulating the output stage indicates that the maximum output achievable >>> is about 1.6V pp into 1M or 0.4Vpp into 50 ohms. >>> However distortion is a bit high. This requires about 0.4Vpp at the >>> input to the buffer. >>> >>> The dc level on the red wire is reasonably consistent with quick >>> simulation of the level without oscillation at an oven temperature of >>> 90-100C. >>> When oscillating the current drawn by the oscillator may increase >>> slightly, bringing the value closer to that observed. >>> >>> Bruce >>> >>> J. L. Trantham wrote: >>> >>> >>> >>>> Well, a little work with a scalpel and a small flat bladed screw driver >>>> >>>> >>>> >>> and >>> >>> >>> >>>> I was able to open the package. Inside is what I call an 'Output Board' >>>> that contains the output circuit and the 'FINE' frequency adjust along >>>> >>>> >>>> >>> with >>> >>> >>> >>>> the 'Oven' which has the 'COARSE' frequency adjust. Attached to the >>>> >>>> >>>> >>> 'Oven' >>> >>> >>> >>>> is what I call the 'Oven Controller Board'. With the removal of 3 >>>> > screws > >>>> and the 'nut' on the 'COARSE' frequency adjust, the 'Oscillator Board' >>>> >>>> >> can >> >> >>>> be removed. >>>> >>>> I have 'derived' the schematic from inspections of the 'Output Board' >>>> > and > >>>> the 'Oscillator Board'. I made no attempt at the 'Oven Controller >>>> > Board' > >>>> since it seems to be operating ok. More on this below. >>>> >>>> I have attached the schematics of the output board and oscillator >>>> > boards. > >>>> >>>> >>>> >>> I >>> >>> >>> >>>> made some measurements of DC and RF voltages on the output board. I >>>> > have > >>>> multiple pictures that are too large to attach. If anyone would like to >>>> >>>> >>>> >>> see >>> >>> >>> >>>> these, I can send them. >>>> >>>> At start up, the 85-50 draws about 0.5A then falls to about 0.25A as the >>>> 'oven' heats up suggesting the temperature regulator circuit is >>>> >>>> >>>> >>> functional. >>> >>> >>> >>>> The 'COARSE' and 'FINE' frequency adjusts work and the frequency can be >>>> brought spot on as compared to my GPSDO. >>>> >>>> I have ordered new transistors in the hope that these are the problem. >>>> > I > >>>> >>>> >>>> >>> am >>> >>> >>> >>>> a little puzzled by the drop in voltage at the 'Red' wire to the oven. >>>> >>>> >> It >> >> >>>> serves both the 'Oscillator Board' and the 'Oven Controller Board'. 2.5 >>>> >>>> >>>> >>> VDC >>> >>> >>> >>>> seems a little low for the oscillator. >>>> >>>> Also, the gain of the output stage of the output board seems a little >>>> >>>> >> low. >> >> >>>> 0.1 V P-P goes to 0.36 V P-P. >>>> >>>> I have a second, good, 85-50 but would like to avoid opening it if >>>> >>>> >>>> >>> possible. >>> >>> >>> >>>> Any help would be appreciated. I hope I made no mistakes on the >>>> >>>> >>>> >>> schematics. >>> >>> >>> >>>> Joe >>>> >>>> >>>> >>>> >>>> -----Original Message----- >>>> From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On >>>> Behalf Of Gordon Batey >>>> Sent: Sunday, May 24, 2009 6:50 PM >>>> To: time-nuts@febo.com >>>> Subject: Re: [time-nuts] Broken Ovenaire OSC 85-50 >>>> >>>> I had an earlier model 20 mhx ovenaire osc that had very low output. I >>>> opened it up with a scalpel and found the TTL chip had failed and was >>>> >>>> >> only >> >> >>>> letting a small amount of the osc signal thru. I was able to use an >>>> external TTl (74LS20 I think) to restore it. As I recall I was unable >>>> > to > >>>> readily get to the chip so I replaced it with an external one. >>>> >>>> Good luck. >>>> >>>> Gordon >>>> >>>> >>>> >>>> _______________________________________________ >>>> 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. >> >> >> _______________________________________________ >> 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.
