Heterodyne Crystal Failures Mode?

[W5EUQ]

I have to commend you on the most scientific report I've seen in years.  
When I was in college, we were taught to go at the problem exactly the 
way you approached the problem.  Congrats to you for a successful 
adventure.  When we succeed, we revel.  I salute you.
Not to mention, thanks, I have some crystals that won't work.....and now 
I know what to do to revive them....  Bob   W5EUQ... Tampa

Jim Flanagan wrote:
> Please excuse me if this accidentally was double posted....
>
> Hi guys..
> Well I spent some time this weekend looking into this xtal issue.  The
> HW-101 that I am restoring had three crystal that would not oscillate:
>
> 22.895 MHz ( 14 MHz Band)
> 37.385 MHz ( 28.5 MHz Band)
> 37.895 MHz ( 29 MHz Band)
>
> What I ended up doing is to take each one out, one at a time, and make a
> quick series resonant measurement using a sig gen and scope.  I could 
> tell
> that there was a 'slight' resonance on each that was somewhat 3-4 kHz 
> higher
> than it should have been.  I also know that these xtals used in a 
> parallel
> mode, but the series resonance was easier for me to check and once the
> series res was found then the parallel res would/should be about 1.5 
> kHz or
> so higher.
>
> Thus, verifying that the crystals *appeared* dead, I used a heat gun 
> to melt
> the solder around the base and remove the cover.  Under a jewelers loop
> there were no discernible fractures, etc.  I made a simple continuity 
> test
> on each leg and all looked OK.  Now the magic.  I used some 99.9% pure
> alcohol with a q-tip and gently cleaned each side of the quartz material.
> Using another Q-tip, dry, I went back over the quartz material to help 
> dry
> out the device.  Upon a recheck using my sig gen/scope, the xtal was 
> again
> functioning!  I carefully resoldered the case, checked again and then
> reinstalled the xtal back into the unit.  Worked like a champ!  Of 
> course,
> time will tell how long the fix is good for.
>
> I then repeated the same procedure for the other two xtals.  Each time 
> with
> success. So, the question is, WHY??  Are the xtals subjected to 
> residue that
> caused them to deteriorate?  When I cleaned them, there was no noticeable
> residue, etc.  I notice that there is a small pin hole on the side of 
> each
> xtal that is soldered shut.  Do they pull a vacuum on xtals?  If not, 
> what
> is the hole for?
>
> Well, there you have it.  I guess the next time a xtal fails, I will try
> this trick to see if I can bring it back to life.
>
> Your comments & criticism are welcome..
> Jim
> WB5KYE
>
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