[Premium-Rx] Replacing capacitors in RA6793

[Charles Steinmetz]

Cornel wrote:

>My Racal 6793 is having trouble with the capacitors, so I will 
>replace them starting with the power supply.
>Is there a document somewhere with a list of all capacitors 
>involved? Which brand and/or type of capacitors are recommended?

There is a document available on the 'net listing the tantalum caps 
in the almost identical RA6790:

<http://www.ra1792.co.uk/radios/80s/RA6790tants.pdf>

That said, I do not recommend a wholesale "shotgun" replacement, 
unless you have experienced multiple failures.

The main filter capacitors are aluminum electrolytics (A10 C1, C4, 
C7, and C10).  Again, I would replace failed caps but would not 
"shotgun" them unless you have suffered multiple failures.

Replace tantalums with new tantalums, and aluminum electrolytics with 
new aluminum electrolytics.  Use the highest temperature rated caps 
you can get (preferably, 125C parts), from a series designated by the 
manufacturer as "high reliability."  Of course, you need to source 
capacitors that will physically fit, so pay attention to the 
dimensions and lead spacing.

I like the Vishay 199D Series solid tantalums.  The AVX TAP Series 
tantalums are also high quality, as are the Kemet "T" Series ("UltraDip II").

Note that the holes in 6790/6793 PC boards are just marginally larger 
than the component leads, so it is often difficult to remove 
components and also very easy to mutilate PC traces.  A good vacuum 
desoldering tool is pretty much a requirement.

Best regards,

Charles