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

[Dr. Gerald N. Johnson]

On Tue, 2008-06-24 at 22:19 -0700, Ron Castro wrote:
> About 10 months ago, the capacitors on the A9 Power Distribution board failed, and I sent the radio back to the factory to get it fixed.  Well, just 10 months later, the same thing happened again.  This time, I decided to fix it myself with premium capacitors purchased through Mouser.  The fix worked!  The 470 uf, 16 Volt, 85 degree C caps, C6, C7 and C9 were replaced with ultra-low ESR 50 Volt, 105 degree C units that fit perfectly in the board.  
> 

What is the fundamental cause of these failures? Are the capacitors poor
to begin with, or is the circuit ripple or voltage excessive? Is there
AC being applied to a DC capacitor? Is one wired in backwards? Is the
environment simply hot from being close to power stages that simply
cooks the capacitors? 

Lots of lowest bid Chinese electrolytics are poorer when new than I find
acceptable, so they age poorly. A few years ago there was a large batch
of capacitors often applied to computer motherboards that exploded when
power was applied for the first time. My guess is that the factory
didn't understand the formation process and hadn't finishing making the
electrolytics.

Certainly the low ESR and high temperature electrolytics are the best
available and because of the low ESR have the best power factor (lowest
losses) and the high temperature rating should give the longest life in
a hot environment.

> I have a whole page on my website for anyone interested, including pictures and ordering information for the caps.  Hopefully, these will last longer than the first two sets!
> 
> http://n6ie.com/A9_Board.mht
> 
>          Ron   N6IE
>       www.N6IE.com
> 
73, Jerry, K0CQ