I just thought of a fifth problem.
With the fan , as original, directing internal air down the long axis of the
fan. The big toroidal would split the air flow at the other end , returning
back to the fan along the outer edges.
As no pressure differential between inside and outside of box , the vents in
the base and rear become useless as any thermal gradient across the box is
lost.

A baffle now added arounfd the fan to take air from outside, through some of
the vents, and direct it back out through the remaining vents.

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Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
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