[time-nuts] Opening an Isotemp OCXO

Graham / KE9H ke9h.graham at gmail.com
Fri Oct 28 12:46:14 EDT 2016


Here is the TI document on "Case Marking."  It may not be a 74S30.

http://www.ti.com/lit/an/snoa039c/snoa039c.pdf

--- Graham

==

On Fri, Oct 28, 2016 at 11:27 AM, Adrian Godwin <artgodwin at gmail.com> wrote:

> That's one sweet soldering iron. Is it an American Beauty ?
>
>
> On Fri, Oct 28, 2016 at 4:31 PM, Peter Reilley <preilley_454 at comcast.net>
> wrote:
>
> > I did finally get it open.   I used a very large old style soldering
> > iron and .003 inch steel shim stock.   I would melt the solder on the
> > straight seams and insert small pieces of the shim.   Solder does not
> > stick well to steel so the shim kept the soldered seam open.
> > I used a soldering iron rather than a torch because I can control the
> > temperature.
> >
> > I could not use the shim at the corners.   After all the straight seams
> > were separated I could pull each corner using a screw in the mounting
> > hole and melt the solder at the corner.   Slowly working my way around,
> > corner by corner, I got it opened.   I did not damage anything so I
> > should be able to close it up after I fix it.
> >
> > Looking around with my scope it seems that the output driver chip is bad
> > as I expected.   It is a TI 14 pin surface mount DIP.   It says S30 on it
> > which if it is a 74S30 it is an 8 input positive NAND gate.   The board
> > layout confirms this as the 10 MHz signal is connected to pin 2 and all
> > other inputs are tied high.   Pin 8 is connected to the output.
> >
> > The chip is run off 12 volts so it must be CMOS.   But I cannot find any
> > chip like that that will run off 12 volts.   Any suggestions for a
> > replacement?
> >
> > Also, using an 8 input NAND chip for a driver seems an odd choice.
> >
> > When I put 12 volts on the unit the S30 chip gets really hot. After I
> > removed the chip the unit seems to work OK.   The current jumps between
> > about .1 amp to .9 amps.   It seems like the temperature regulator is
> > an on/off type controller.
> >
> > The device on eBay, item 261920574725, looks exactly like what I have.
> >
> > I have placed a bunch of pictures in my dropbox.
> > https://www.dropbox.com/sh/52e9d1rva9kpb3w/
> AABmbIj1aK7Zk2J9SNMmu-JAa?dl=0
> >
> > Pete.
> >
> >
> >
> >
> > On 10/18/2016 10:57 AM, J. L. Trantham wrote:
> >
> >> Pete,
> >>
> >> I'm not familiar with your OCXO but I found one shown on 'theBay' (item
> >> 261920574725) and it appeared to have an option for 'mounting screws',
> four
> >> of them, on the bottom.  Interestingly, the 'link' to the datasheet for
> >> that unit did not show threads for mounting screws.
> >>
> >> If your unit has that option, I would suggest placing four long screws,
> >> mounting the item in a vise, use a small torch (I've used a hand held
> >> propane torch turned down very low to open a number of units from
> 5061A's)
> >> around the bottom of the case while gripping the top with an appropriate
> >> sized Channel Lock plier and lifting off the top.
> >>
> >> If you can repair the OCXO, it should be easy to reassemble the unit
> with
> >> solder.
> >>
> >> TheBay unit looks like it has a screw cover (which likely has a rubber
> >> gasket) for mechanical adjustment of the frequency.  I'd remove that
> before
> >> applying the torch. :^).
> >>
> >> If you get it open, I'd love to see some pictures of the insides.
> >>
> >> Good luck and hope this helps.
> >>
> >> Joe
> >>
> >>
> >>
> >> -----Original Message-----
> >> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Peter
> >> Reilley
> >> Sent: Tuesday, October 18, 2016 8:11 AM
> >> To: time-nuts at febo.com
> >> Subject: [time-nuts] Opening an Isotemp OCXO
> >>
> >> 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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> >>
> >>
> >>
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