I get a 'if working correct' Vcc of about 3.5V If the Vcc is 2.49 volts, I calculate a 3ma unaccounted for current draw from something. So I have same conclusion, one or more of the following is wrong. 510 Ohm too high, 5 volts too low, un-shown current draw thru Leakey caps or extra circuits or bad data. (plus the pot is (and should be) more likely a 10 K ohm)
ws ****************** ----- Original Message ----- From: "Bruce Griffiths" <bruce.griffi...@xtra.co.nz> To: "Discussion of precise time and frequency measurement" <time-nuts@febo.com> Sent: Friday, July 03, 2009 11:58 PM Subject: Re: [time-nuts] Broken Ovenaire OSC 85-50 > Warren > > The Vcc dc current doesn't change much if the circuit is oscillating (at > least it shouldn't if the circuit operating correctly - the active > devices aren't supposed to saturate as thats adds too much phase noise). > > My simulations were over the 50-100C rang although temperature doesn't > affect the currents and voltages too much. > They also don't include loading of the frequency control pot wiper. > > There is no major inconsistency other than the effect of the > unanticipated loading of the EFC pot wiper. > The simulated oscillator Vcc is actually about 3V when everything is > working properly. > NB its important to use models that accurately reflect the correct > transistor junction area just blindly tossing in 2N3904's increases the > current somewhat as the Vbe is lower for a given current than the actual > transistors. The simulated oscillator Vcc is then closer to 2.5V. > > Earlier circuit schematics didn't include as many actual measured dc > voltages. > > Bruce > > WarrenS wrote: >> Bruce >> >> 4ma? Interesting, Maybe IF the Osc was running, BUT >> My DC calculations of the present values I can read on Schematics come to >> 1.3ma + 0.26 = 1.58 ma load on the 510 ohm >> >> With it NOT osc, which is almost the present case, >> the Only Dc current drawn is. >> >> 1.75 V on 20K = 0.08ma (Q1 bias) >> 1.04 V on 2.2K = 0.47ma (Q1 collector) >> 0.365V on 470 ohm. = 0.77 ma (Q2 emitter) >> Osc board =1.32 ma >> >> Buffer board >> (2*4.7k) at 2.49 V = 0.26 ma >> >> >> Also note that the 4.7 K ohm pot and 4.7K divider voltages show excess >> current draw somewhere, maybe on the Grn lead bypass cap.. >> >> ws >> >> ************** >> >> ----- Original Message ----- >> From: "Bruce Griffiths" <bruce.griffi...@xtra.co.nz> >> To: "Discussion of precise time and frequency measurement" >> <time-nuts@febo.com> >> Sent: Friday, July 03, 2009 11:08 PM >> Subject: Re: [time-nuts] Broken Ovenaire OSC 85-50 >> >> >> >>> Warren >>> >>> My Spice model of the dc levels in the oscillator indicate a current >>> more like 4mA in the 510 ohm resistor. >>> >>> Bruce >>> >>> WarrenS wrote: >>> >>>> I just saw your schematic of the rest of the buffer circuit. Sorry I >>>> missed it early. >>>> >>>> The Osc Vcc is shown driven from a 510 Ohm resistor, and with the total >>>> current thru the 510 res at under 2 ma, >>>> Looks like Osc Vcc should be at more like 4.0 volts instead of 2.49 volts. >>>> If I'm correct about that (this time) then, It has got to be one of three >>>> things. >>>> The 510 ohm is wrong, the 5 volts is wrong, or the load on the 510 ohm is >>>> wrong. >>>> It should be easy enough to measure which one it is. >>>> The voltage at the junction of the two 4.7K resistors are WRONG. >>>> Looks like it is caused by an excess current draw on the Grn lead. >>>> Check the direction and leakage of the voltage controlled cap diode and >>>> bypass. >>>> If all else is right, Look for the cause of the extra loading current on >>>> the 510 ohm, >>>> >>>> WS >>>> >>>> **************** >>>> >>>> ----- Original Message ----- >>>> From: "Bruce Griffiths" <bruce.griffi...@xtra.co.nz> >>>> To: "Discussion of precise time and frequency measurement" >>>> <time-nuts@febo.com> >>>> Sent: Friday, July 03, 2009 9:55 PM >>>> Subject: Re: [time-nuts] Broken Ovenaire OSC 85-50 >>>> >>>> >>>> >>>> >>>>> WarrenS wrote: >>>>> >>>>> >>>>>> A couple more thoughts; >>>>>> >>>>>> Is the VCC (Red wire) current draw correct?. >>>>>> Should be 1.3 ma (per the schematic values) with the 470 Ohm and >>>>>> more like 7 plus ma with the 47 ohm. >>>>>> >>>>>> AND I don't remember seeing, IS the Freq real close AND can it be tuned >>>>>> by the cap and Green wire voltage? >>>>>> If both answers are YES, at least most things are working correctly. >>>>>> >>>>>> As Bruce said: >>>>>> >>>>>> >>>>>> >>>>>>> "if the resistor values are correct this is the voltage(s) that one >>>>>>> should get" >>>>>>> >>>>>>> >>>>>>> >>>>>> With the resistors values shown, I agree that all the other voltages are >>>>>> correct given the 2.49 volts, >>>>>> BUT the 2.49 volt is NOT controlled by any of the values on that >>>>>> schematic, it's just an input. >>>>>> AND the output amplitude is not yet being controlled by current cut off. >>>>>> >>>>>> Something that needs to be asked is are all these the correct values. >>>>>> It sounds like you got them by measuring and not from a "should be" >>>>>> schematic. >>>>>> >>>>>> One last, way out thought. >>>>>> It was my belief that very good osc have some sort of AGC to control the >>>>>> amplitude, >>>>>> ANY chance that the VCC is used as the input to control the amplitude of >>>>>> the Osc output? >>>>>> If so, could it be that the external AGC that is what broken and >>>>>> supplying too low a VCC voltage to the circuit? >>>>>> >>>>>> ws >>>>>> >>>>>> >>>>>> >>>>>> >>>>> The Colpitts crystal oscillator limits the crystal current by being >>>>> periodically cutoff for part of the cycle. >>>>> There is an optimum duty cycle (usually something like 25%) that >>>>> corresponds to minimum phase noise. >>>>> The oscillator dc collector current determines the crystal current and >>>>> hence the output amplitude. >>>>> It is possible to perform AGC by varying the oscillator Vcc but the >>>>> output amplifier schematic appears to have no circuitry for this. >>>>> Some circuits actually do this, but the oscillator transistor is still >>>>> cutoff for part of the oscillator cycle. >>>>> The oscillator VCC is fed from a tap in a resistive divider network >>>>> (located on the external (to the oven) buffer board) connected between >>>>> the 5V supply and ground. >>>>> Usually one just varies the emitter (or collector) dc current by >>>>> selecting a resistor value. >>>>> >>>>> Bruce >>>>> >>>>> >>>>>> ***************** >>>>>> ----- Original Message ----- >>>>>> From: "Bruce Griffiths" <bruce.griffi...@xtra.co.nz> >>>>>> To: "Discussion of precise time and frequency measurement" >>>>>> <time-nuts@febo.com> >>>>>> Sent: Friday, July 03, 2009 8:21 PM >>>>>> Subject: Re: [time-nuts] Broken Ovenaire OSC 85-50 >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>>> WarrenS wrote: >>>>>>> >>>>>>> >>>>>>> >>>>>>>> Here is my two cents worth >>>>>>>> 20 mv output, sure sounds like something is broken. >>>>>>>> It should be fixed before it is modified. >>>>>>>> The 2.49 volts on the Red input voltage seem LOW, More Vcc maybe. >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>> Not so, if the resistor values are correct this is the voltage that one >>>>>>> should get. >>>>>>> The question that remains: Is the voltage what the designer intended? >>>>>>> With the Colpitts oscillator used limiting in the oscillator transistor >>>>>>> (usually by current cutoff) is used to limit the amplitude. >>>>>>> Just increasing the voltage without checking the resultant crystal >>>>>>> current will be within permissable limits can be counter productive. >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>>> The "Grn" labeled wire, FreqCtrl input should be about 1/2 VCC for >>>>>>>> testing. >>>>>>>> If you do 'need' to modify the gain, >>>>>>>> It would seem better to bypass the 470 ohm resistor with a cap in >>>>>>>> series with the 47 ohms. >>>>>>>> >>>>>>>> ws >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>> Bruce >>>>>>> >>>>>>> >>>>>>> >>>>>>>> ******************** >>>>>>>> ----- Original Message ----- >>>>>>>> From: "Mike Monett" <xde-l...@myamail.com> >>>>>>>> To: <time-nuts@febo.com> >>>>>>>> Sent: Friday, July 03, 2009 11:50 AM >>>>>>>> Subject: Re: [time-nuts] Broken Ovenaire OSC 85-50 >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>>> > An update on the Broken Ovenaire OSC 85-50. >>>>>>>>> >>>>>>>>> > I prepared a 'schematic' of the Output Board and the Oscillator >>>>>>>>> > Board (attached) and I have lots of pictures of the external unit >>>>>>>>> > and the insides if anyone is interested. >>>>>>>>> >>>>>>>>> > I resoldered all connections and replaced all transistors on the >>>>>>>>> > Output Board and the Oscillator Board all to no benefit. I >>>>>>>>> > measured all the components with an LCR meter and found the 0.01 >>>>>>>>> > uF bypass on the 330 ohm resistor in the emitter circuit of the >>>>>>>>> > output transistor of the Output Board to be low and with a high >>>>>>>>> > ESR. I replaced this with about a 20% increase in output amplitude >>>>>>>>> > but still inadequate. I replaced the rest of the 0.01 uF caps on >>>>>>>>> > the output board with no additional benefit. I transiently >>>>>>>>> > disconnected the Red wires from the Oven Controller board and >>>>>>>>> > there was no increase in output or significant increase in voltage >>>>>>>>> > to the Oscillator Board. >>>>>>>>> >>>>>>>>> > Therefore, it appeared that a 'low output crystal' (if such a >>>>>>>>> > thing exists) was the only logical explanation that I could come >>>>>>>>> > up with. That seeming to be the case, there appeared to be only 4 >>>>>>>>> > options. 1. Toss the OCXO (sorry, too much effort so far). 2. >>>>>>>>> >>>>>>>>> > Build an external amplifier (seemingly too much additional >>>>>>>>> > effort). 3. Try to adjust on the bias of the oscillator transistor >>>>>>>>> > to achieve a higher output (seemed too 'iffy'). Or 4. Lower the >>>>>>>>> > value of the resistor in the emitter circuit of the Oscillator >>>>>>>>> > Board to get more gain out of the last stage in the Oscillator >>>>>>>>> > Board. >>>>>>>>> >>>>>>>>> > I replaced the 470 ohm resistor with a 47 ohm resistor and the >>>>>>>>> > amplitude increased to about 0.4 V P-P into a 50 ohm load and was >>>>>>>>> > sufficient to make it a usable OCXO again. >>>>>>>>> >>>>>>>>> > I reassembled, resealed with Epoxy and all seems well so far. >>>>>>>>> >>>>>>>>> > If anyone wants pictures or other info, please let me know. >>>>>>>>> >>>>>>>>> > Thanks for all the suggestions and help. >>>>>>>>> >>>>>>>>> > Joe >>>>>>>>> >>>>>>>>> Joe, >>>>>>>>> >>>>>>>>> Congratulations on getting your system to work! >>>>>>>>> >>>>>>>>> A couple of things. First, trying to measure the currents in the >>>>>>>>> circuit with a ferrite toroid won't do you much good. You don't know >>>>>>>>> what the currents should be, and the secondary of the toroid >>>>>>>>> transformer requires a termination resistor. The value changes with >>>>>>>>> the turns ratio. >>>>>>>>> >>>>>>>>> Just from looking at the circuit, the RF currents will be extremely >>>>>>>>> low. This requires a large number of turns on the secondary, which >>>>>>>>> will probably resonate at or below the 10MHz operating frequency due >>>>>>>>> to stray capacitance from the connection to the scope. So it is >>>>>>>>> unlikely you will get any useful progress in this direction. >>>>>>>>> >>>>>>>>> However, from the values on your schematic, the output tank circuit >>>>>>>>> resonates at 9.602MHz with a Q of 9.6. So the tank is already well >>>>>>>>> below resonance, which attenuates the output voltage. >>>>>>>>> >>>>>>>>> Any stray capacitance you add to the circuit will bring the resonant >>>>>>>>> frequency lower, further aggravating the loss in signal. >>>>>>>>> >>>>>>>>> The output tank is tapped with the 75pF and 91pF in series. This >>>>>>>>> further attenuates the signal. >>>>>>>>> >>>>>>>>> I'd change the circuit to a single capacitor across the tank with a >>>>>>>>> small trim capacitor to tune it to resonance. >>>>>>>>> >>>>>>>>> To get the signal into 50 ohms for distribution, I'd add a limiter >>>>>>>>> if you can tolerate a square wave output, or a good emitter follower >>>>>>>>> if you need a sine wave. Take the output from the collector of the >>>>>>>>> 2N2369 to get the maximum signal amplitude. >>>>>>>>> >>>>>>>>> Your original post mentions an output amplitude of 20mV. If the >>>>>>>>> normal amplitude is around 2V, this represents a loss of 40dB. This >>>>>>>>> is a huge loss in signal. The circuit obviously worked at one time, >>>>>>>>> so there may well be some other hidden problem. >>>>>>>>> >>>>>>>>> It is possible the crystal is damaged, but this seems unlikely. A >>>>>>>>> crystal oscillator probably won't even start if the signal level is >>>>>>>>> down 40dB. >>>>>>>>> >>>>>>>>> You can check the oscillator and crystal in SPICE. Normally, the >>>>>>>>> high Q of the crystal will make the analysis very slow. It could >>>>>>>>> take many hours for the simulation to begin oscillating and >>>>>>>>> stabilize at the final amplitude. The transient analysis requires a >>>>>>>>> very fine time step for accuracy, and you could run out of memory >>>>>>>>> before the simulation was complete. >>>>>>>>> >>>>>>>>> I have developed a much faster way of analyzing a crystal oscillator >>>>>>>>> in SPICE. Instead of requiring tens or hundreds of thousands of >>>>>>>>> simulated cycles, this method gives accurate results in only a few >>>>>>>>> dozen cycles. For more information, please see "SPICE Analysis of >>>>>>>>> Crystal Oscillators" >>>>>>>>> >>>>>>>>> http://pstca.com/spice/xtal/clapp.htm >>>>>>>>> >>>>>>>>> You can estimate the value of the crystal ESR by finding the Q of >>>>>>>>> your crystal and working backwards. >>>>>>>>> >>>>>>>>> I'm attaching a gif of your schematic for reference. This is rotated >>>>>>>>> 90 degrees and enhanced in LView Pro to improve the contrast. >>>>>>>>> >>>>>>>>> Please let me know if you have any questions. >>>>>>>>> >>>>>>>>> Thanks, >>>>>>>>> >>>>>>>>> Mike >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>> _______________________________________________ >>>>>>>> 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.