[time-nuts] 5MHz ocxo- Opening Solder sealed cans

[Didier Juges]

Silver solder has a higher melting temperature so make sure you adjust your soldering iron to the right temperature otherwise you will just make another cold joint.

Also wick all the old solder before making a new joint with different solder. 

Didier KO4BB


Ron Ward <n6idlron at comcast.net> wrote:

>Hi:
>I have been looking at the poor quality solder joints on the
>oscillator.
>If you have a steady hand and a small tipped soldering with silver
>baring (about 2% silver) solder, I would re-solder the connections.
>Many
>of them do not look properly "wetted" and cold. Some of the heat from
>removing the top may have re-soldered a problem connection.
>Ron
>
>-----Original Message-----
>From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
>Behalf Of Paul Flinders
>Sent: Thursday, July 26, 2012 2:59 PM
>To: Discussion of precise time and frequency measurement
>Subject: Re: [time-nuts] 5MHz ocxo- Opening Solder sealed cans
>
>On 26/07/12 20:49, Tom Miller wrote:
>> Pick up a few sticks of ChipQuik and mix it in with a good iron.
>Then,
>
>> you may do just what you say. It should melt below about 95°C.
>> A good hot air heat gun would most likely do the trick. Maybe use
>some
>
>> solder wick first to lower the amount of tin/lead solder. Then add
>the
>
>> chipquik.
>>
>> You might also just solder a tab on the bottom then you could clamp 
>> the top in a leather jawed vise. Hit it with a hot air gun while 
>> pulling on the base tab.
>>
>
>Well, a few exploratory attempts confirmed my initial suspicion that I 
>don't have a soldering iron big enough for the job - the largest I have
>
>is 60W or so, and the hot air gun didn't touch it even set to 480deg C
>
>So, I reached for the next larger source of heat which is a small 
>blowtorch I have, set a small flame and ran it round the whole seam
>then
>
>pulled the top off with a gloved hand. Things did get a bit warm but 
>only for a short while.
>
>The first thing I encountered was some insulating foam - this was
>rather
>
>sticky. Not sure whether it had gone like that over time or due to my 
>heating the whole thing a bit too much. On three sides the foam was 
>separated from the case by what looks like some thin SRBP. This had 
>blistered a bit so obviously things were a bit hot just there but the 
>foam was much the same whether "protected" by the SRBP so I'm wondering
>
>whether this has just disintegrated over time.
>
>Pulling/washing the foam off reveals three PCBs and a further enclosed 
>metal case with the crystal. A TIP21 bolted to this acts as the heating
>
>element. Originally there had been some cable ties anchoring the
>crystal
>
>enclosure but these were brittle - presumably from the heat of the
>oven.
>
>Hooking the unit up to 12V and an oscilloscope shows that it has 
>survived the encounter with the blow torch and produces a nice 5MHz
>sine
>
>wave at 2.5V p-p (into 10Meg ohm). Irritatingly it doesn't really want 
>to misbehave - presumably because whatever didn't like the heat is now 
>cooler with the insulating foam removed. The inner metal case gets too 
>hot to touch but the thermostat seems to be working because the current
>
>drawn drops from about 380mA to 240 or so. It should probably be lower 
>but, again, without the usual amount of insulation it's likely to draw 
>more keeping the oven up to temperature.
>
>So, as it doesn't want to misbehave, I'm not totally clear which way to
>
>go. The output does drop to about 1.8V p-p when the oven is fully warm 
>which might be related to the original fault. I suppose the fact that 
>the fault has "gone away" eliminates the oven assembly or crystal
>itself
>
>as the source of the problem.
>
>Photos for comments or curiosity. The black stuff all over the PCBs is 
>the remains of the foam.
>
>http://www.wild-pc.co.uk/images/P1020364.jpg
>http://www.wild-pc.co.uk/images/P1020367.jpg
>http://www.wild-pc.co.uk/images/P1020368.jpg
>http://www.wild-pc.co.uk/images/P1020369.jpg
>http://www.wild-pc.co.uk/images/P1020370.jpg
>
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