[time-nuts] Broken Ovenaire OSC 85-50

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed May 27 03:42:39 UTC 2009


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.





More information about the Time-nuts_lists.febo.com mailing list