[TenTec] Orion II A9 Board Failure...Again!

[Dr. Gerald N. Johnson]

On Fri, 2008-06-27 at 14:07 -0700, Jim WA9YSD wrote:
> Jerry your right, but after thinking more about it and whats going 
> on it is a function of both drying out and the chemical action 
> because of the paste getting either more acidic or alkaline.  
> I only got past Chem 102 either one is corrosive enough to do damage.
> 
>  Keep The Faith, Jim K9TF/WA9YSD

My capacitor book says, "an aqueous solution of ammonium borate, boric
acid, and glycol." Its strong enough to eat the aluminum oxide created
in the forming process. That mix sounds acidic.

If the seals hold, the capacitor should not dry out, but if the seals
vent that's electrolyte gone from the capacitor, effectively drying it.

Chemical reactions double their speed for each 10 degree C rise in
temperature so running hot speeds up the demise of the capacitor even if
the seal doesn't vent.

The fundamental problem with too much ripple current is heat and that
makes the vent release precious electrolyte and makes the chemical
reactions eat the aluminum oxide faster and so the hot electrolytic goes
bad fast. Miniature electrolytics seem to be the poorest for survival
and I suspect much solid state equipment performance has fallen over a
decade or two of use due to electrolytic capacitor aging and that
performance could be restored by shotgun replacing every aluminum
electrolytic with the highest temperature rating, lowest ESR capacitors
available taking into account the required ripple current capacity. But
I've not attacked any equipment to do that yet. At least not the whole
radio, but that's how I fixed a switching supply in my FT-736. I pulled
all the control circuit electrolytics and put in new ones and it worked.
I did check the ones I pulled and all were very bad on my capacitor
bridge.

73, Jerry, K0CQ