[time-nuts] Wenzel Oscillator Repair

Ed Palmer ed_palmer at sasktel.net
Tue Jan 20 23:35:12 UTC 2009


I was reluctant to consider a torch because I haven't done it and didn't 
want to cause any more damage.  The second (and more serious) reason is 
that I live in an apartment.  My office / computer room / mad 
scientist's lab is actually a bedroom complete with carpet.  Soldering 
irons I can deal with.  Open flames however, are not going to happen.  
In summer I could go out on the balcony, but right now there's a foot or 
two of snow out there.

In any case, the deed is done.  My plan was to use a Dremel with a metal 
disc coated with diamond dust to cut into the solder seam.  However, 
since the sides of the oscillator were slightly bowed, I had to decide 
whether to sacrifice the can or the bottom.  I chose the bottom.  Pretty 
much destroyed it, but the can barely has a mark on it.  I think I can 
fabricate a new bottom - I'll probably attach it with screws rather than 
resoldering it.  When I look inside the can I can see the solder.  It 
extends about 4 mm from the edge.  A torch was the only other way I 
could have gotten it apart.

The problem with the oscillator turned out to be even easier to fix than 
I could have hoped for.  There's a ferrite transformer on the output - 
possibly a balun.  The wire is about the thickness of a hair.  The 
ferrite isn't tied down - it's just held by the leads.  I don't know if 
it took a physical hit or if the solder just dissolved the wire over the 
years, but one of the leads had broken.  I resoldered it and instead of 
a wobbly level of -20 to -30 dbm into 50 ohms, I now have a much more 
satisfying level of ~ +12 dbm.  And the levels in the rest of the unit 
now make sense.  Instead of hitting a Minicircuit RPD-1 Phase Detector 
with a level around -30 dbm, it's now seeing a level of +7 dbm - just 
what it should be.

I'd like to thank you, John,  and everyone else  for their ideas.  They 
were a great help.

Ed

> Message: 1
> Date: Tue, 20 Jan 2009 09:28:31 -0800
> From: "John Miles" <jmiles at pop.net>
> Subject: Re: [time-nuts] Wenzel Oscillator Repair
> To: "Discussion of precise time and frequency measurement"
> 	<time-nuts at febo.com>
> Message-ID: <PKEGJHPHLLBACEOICCBJCEGCBCAC.jmiles at pop.net>
> Content-Type: text/plain; charset="us-ascii"
>
> You probably have a lot more room to play with, given the larger housing on
> your OCXO.  The ULN series is rather densely packaged, and that was one
> reason why I wasn't crazy about going after it with a propane torch.  In
> your case I'd be tempted to try the torch method before actually damaging
> the housing with a Dremel tool.
>
> While fixing a couple of Ovenaire OCXOs that use a similar form factor, I've
> noticed that their PC board edges don't come anywhere near the endcap.  The
> Ovenaire parts were sealed with epoxy, so a heat gun was all that was needed
> to open them, but I'm sure I could've opened them with a torch without
> hurting anything, if they'd been soldered shut.
>
> -- john, KE5FX
>
>   
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
>> Behalf Of Ed Palmer
>> Sent: Tuesday, January 20, 2009 5:59 AM
>> To: time-nuts at febo.com
>> Subject: Re: [time-nuts] Wenzel Oscillator Repair
>>
>>
>> Now I understand!  I was planning to reuse the case.  It didn't occur to
>> me to sacrifice the case and put the oscillator in another box.
>>
>> Thanks for the idea, John.
>>
>> Ed
>>
>>     
>>> Message: 3
>>> Date: Mon, 19 Jan 2009 21:20:54 -0800
>>> From: "John Miles" <jmiles at pop.net>
>>> Subject: Re: [time-nuts] Wenzel Oscillator Repair
>>> To: "Discussion of precise time and frequency measurement"
>>> 	<time-nuts at febo.com>
>>> Message-ID: <PKEGJHPHLLBACEOICCBJMECCBCAC.jmiles at pop.net>
>>> Content-Type: text/plain; charset="us-ascii"
>>>
>>> I used a fiberglass-reinforced cutoff wheel.  This can open practically
>>> anything, but it puts a lot of vibration and dust into the innards of
>>> whatever you're taking apart.  My guess was that this was safer
>>>       
>> than using a
>>     
>>> torch.
>>>
>>> Since I wasn't going to be able to maintain the original hermeticity, I
>>> remounted the oscillator in a Hammond box, like so:
>>>
>>> http://www.thegleam.com/ke5fx/w1.jpg
>>>
>>> I brought the trimmer (which was also damaged in this
>>>       
>> particular oscillator)
>>     
>>> and oven-status LED out to the box lid, along with the four original
>>> terminals.  Makes a nice package that can be easily opened for
>>>       
>> maintenance:
>>     
>>> http://www.thegleam.com/ke5fx/w2.jpg
>>>
>>> The repackaged OCXO seems to work fine.  I haven't made any hardcore
>>> measurements with it but I can tell just by watching the
>>>       
>> counter that its
>>     
>>> short-term stability is similar to my other unmolested 5 MHz ULN.
>>>
>>> -- john, KE5FX
>>>
>>>       
>>>> -----Original Message-----
>>>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
>>>> Behalf Of Ed Palmer
>>>> Sent: Monday, January 19, 2009 4:07 PM
>>>> To: time-nuts at febo.com
>>>> Subject: Re: [time-nuts] Wenzel Oscillator Repair
>>>>
>>>>
>>>> I hadn't thought of using a Dremel.  Did you use an abrasive wheel or a
>>>> steel cutter?  The case on mine looks to be about 20 ga. tin-plated
>>>> steel (~0.04" thick).  The gap is so small it might have been
>>>>         
>> a friction
>>     
>>>> fit to start with.
>>>>
>>>> Ed
>>>>
>>>>         
>>>>> From: "John Miles" <jmiles at pop.net>
>>>>> Subject: Re: [time-nuts] Wenzel Oscillator Repair
>>>>> To: "Discussion of precise time and frequency measurement"
>>>>> 	<time-nuts at febo.com>
>>>>> Message-ID: <PKEGJHPHLLBACEOICCBJMEPMBBAC.jmiles at pop.net>
>>>>> Content-Type: text/plain; charset="us-ascii"
>>>>>
>>>>> I had a similar problem with a 5 MHz OCXO from their ULN
>>>>>
>>>>>           
>>>> series.  There was
>>>>
>>>>         
>>>>> a bad solder joint on the output connection, easy enough to fix
>>>>>
>>>>>           
>>>> once I got
>>>>
>>>>         
>>>>> the unit open.
>>>>>
>>>>> In my case I used a Dremel tool to cut the seam.  Suggest
>>>>>           
>> wearing a dust
>>     
>>>>> mask, obviously, and keep your cuts close to the perimeter of
>>>>>
>>>>>           
>>>> the can, in
>>>>
>>>>         
>>>>> case the PC board comes right up to the edge like mine did.
>>>>>
>>>>> -- john, KE5FX
>>>>>
>>>>>           
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>>>>         
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