[time-nuts] Broken Ovenaire OSC 85-50

[J. L. Trantham]

Bruce,

Thanks for your analysis.  Is this all in your head or do you use a computer
program?

If I understand correctly, you are using the term 'buffer' to describe what
I call the 'Output Board'.  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.

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.