[time-nuts] Opening an Isotemp OCXO

Adrian Godwin artgodwin at gmail.com
Fri Oct 28 12:27:49 EDT 2016

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>

> 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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