[time-nuts] Opening an Isotemp OCXO

[paul swed]

if its the yellow tantalum. then yes 39 uf at 10V.
Soooo sort of surprised it didn't go nuclear on you.
Makes for a serious mess.
Regards
Paul
WB8TSL

On Sat, Oct 29, 2016 at 9:59 AM, Bob Camp <kb8tq at n1k.org> wrote:

> Hi
>
> If the OCXO was designed for a ~70 C upper end temperature spec, then a
> ~90C crystal
> would make sense.
>
> When you feed +12 into the oven control, you are increasing the effective
> gain of the control
> loop (it has more power). The cycling you see is the loop going into
> oscillation. It’s the same thing that happens if
> you put way to much insulation around an OCXO.
>
> I *hope* the 4 amps below is a typo. 20W into the beast is way to much.
> 0.4 A at 5V would be
> 2W. That is a fairly normal number for an OCXO like you have at room
> temperature.
>
> Bob
>
>
> > On Oct 29, 2016, at 9:51 AM, Peter Reilley <preilley_454 at comcast.net>
> wrote:
> >
> > More information;
> >
> > I added a picture to the dropbox from my Flir IR camera.   The picture
> shows the copper block
> > that the crystal is attached to running at about 200 F.   In the IR shot
> the copper block is to the
> > right.    In most of the regular pictures it is toward the bottom of the
> picture.    This is with the
> > unit (minus the S30 chip) running on 5 volts for more than 10 hours.
>  Is that too hot?
> >
> > While running at 5 volts the current is constant at about 4. amps, no
> cycling.   At 12 volts
> > it cycled between .9 to .1 amps.   I would not expect cycling for the
> temperature control
> > of an OCXO.   I would expect a linear temperature control circuit.
> >
> > I looked at the tantalum capacitor on the bottom of the board.   The
> marking is 39-10.
> > Does that mean 39 uF and 10 volts?   If so then it must be a 5 volt
> unit.   The capacitor
> > did not explode at 12 volts.
> >
> > Dropbox link:
> > https://www.dropbox.com/sh/52e9d1rva9kpb3w/
> AABmbIj1aK7Zk2J9SNMmu-JAa?dl=0
> >
> > Pete.
> >
> > On 10/18/2016 9:11 AM, Peter Reilley wrote:
> >> I bought an Isotemp OCXO82-59 with a frequency of 10 MHz for a $3 at
> the MIT flea market.
> >> As expected it was dead.   It heats up as expected but looking at the
> output with a scope there
> >> is nothing.   However looking at the output with a spectrum analyzer I
> can see a faint 10 MHz
> >> signal.   It seems that the oscillator is running but the output
> circuitry is dead.   Reasonable
> >> assumption?
> >>
> >> Anyway, has anyone had any luck unsoldering the tin case without
> destroying it?
> >>
> >> Pete.
> >>
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