[time-nuts] Broken Ovenaire OSC 85-50

Bruce Griffiths bruce.griffiths at xtra.co.nz
Fri May 29 03:43:33 UTC 2009


Joe

Oven board solder joints are more likely suspects.
Check all inductors for continuity and measure all resistors.

Bruce

J. L. Trantham wrote:
> 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-bounces at febo.com [mailto:time-nuts-bounces at 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-bounces at febo.com [mailto:time-nuts-bounces at 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-bounces at febo.com [mailto:time-nuts-bounces at 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-bounces at febo.com [mailto:time-nuts-bounces at 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-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
>>>>> Behalf Of Gordon Batey
>>>>> Sent: Sunday, May 24, 2009 6:50 PM
>>>>> To: time-nuts at 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 at 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 at 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 at 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 at 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 at 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 at 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 at 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 at 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 at 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 at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
>   




More information about the time-nuts mailing list