[QuadList] Colortec board 12 capacitor corrosion

[Chill315 at aol.com]

I had this problem wit a machine in service in the 70's.  It was one  of 
the caps that leaked and ate the board.  I do not think this is an age  factor 
or environment.  It just happens.  I think that if I had done  inspections 
rather than wait it would have been caught.
 
As they say, s--- happens!
 
Chris Hill
 
 
In a message dated 11/12/2012 1:56:46 P.M. Eastern Standard Time,  
leodham at centurylink.net writes:





Hi Don & Park, 
Yeah I wondered a little bit about why/how such a big mess was made, too.  
This particular colortec may have been exposed to extreme temperature 
changes  over a period of time in an uncontrolled storage situation. 
I'm thinking it was one of the spare pieces that came from out back of the  
Winston-Salem cat house guy.  The fellow's name escapes me, but I do  
remember all those cats running around all inside the  building.  There were a 
couple tractor trailers full  of equipment & various parts-pieces parked out 
back and this  colortec came from one of those vans I'm pretty sure. 
Maybe  the 15-20 degree freezing temperatures made them pop, or the  120 
degrees inside heat in the summer. 
The last batch of those exact OEM type caps I purchased was at  Sky Craft 
in Florida last Feb. after the Orlando hamfest. $4.  dollars each for 270 uf. 
I shoulda bought more! haha. 
At this late date, I really want to stay as true to original as possible.  
Those oem's have lasted for 40+- yrs, a tall order for any electrolytic. 
Many  years ago attending the engineering program at NE State Tech, I was  
taught that electrolytics have a shelf life; ie., they will go bad new  sitting 
on the shelf after enough time passes and the electrolyte dries out  enough. 
The sealed 'wet' caps were an attempt at stabilizing and extending the  
useable life by keeping the electrolyte stable(from drying out). 
Seems that idea worked pretty good! 
Larry Odham 
Quad Tape Transfer 
_www.QUADTAPEXFER.com_ (http://www.quadtapexfer.com/)  


 
____________________________________


Hi Larry:

I've seen a few failures like this, but not this  bad!!!
 
Most of the tantalums that Ampex used in the quad era were mil-spec,  
hermetically sealed units, and they almost never go bad.  However, these  
particular ones are wet tantalums which are not hermetically sealed.   Since these 
are simply filters across the power supply busses, you could  replace them 
with modern-day electrolytics which are small enough  these days to fit in 
the space available.  However, if you insist on the  "original" parts, they 
are still available from suppliers like Avnet or Arrow,  but you'll pay $40 to 
$50 EACH for them.  I did spot a few on eBay for  $15/ea....a real deal!!!
 
I have seen some instances where a board was "shotgunned" and all of the  
expensive hermetically sealed caps (the ones that almost never fail!!!) were  
exchanged for cheap electrolytics.  I've never believed in doing that,  
because I've experienced more failures with the new  electrolytics than with 
the old mil-spec caps.  But in the case of  actually needing to replace one of 
the expensive caps, if we don't have the  original part, I'll go with an 
electrolytic unless the customer requests  otherwise.
 
Don Norwood
Digitrak Communications, Inc.
_www.digitrakcom.com_ (http://www.digitrakcom.com/) 





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