The Memotech MTX Series
The FDX EMI/RFI Filter
The cylindrical silver component close to the FDX case fan is
EMI/RFI filter. It is intended to protect the FDX from
the detrimental effects of EMI/RFI present on the AC power line,
as well as ensuring that interference generated by the FDX
itself is not propagated to other devices connected to the power
I expect that as well as the technical requirement of protecting the FDX from AC line
interference and the effect of the AC powered case fan, the
filter would originally have been installed to meet
As an aside, though it probably makes little
practical difference in this case, operation of the filter can
be compromised to some extent by poor wiring practices. There
should be maximum separation between the power input lines and
the output wiring from the filter. The photo above shows that
Memotech didn't take much care in routing the wires to/from this
filter - other examples I have seen are even worse with the
input and output wires running in parallel across the filter
It is also worth noting that the transformer
adjacent to the fan is not typical - in this example it is
because Memotech had used a 115VAC fan in a 240VAC powered FDX.
This is a
typical circuit diagram for one type of EMI/RFI
Power Solutions website
|Is the filter required today?
think that it depends on the power supply. If the
original FDX PSU is installed, I would retain the
filter to protect the FDX electronics.
However, as I was
replacing the FDX PSU with a
modern PC supply, then I don't think that the filter
is required, particularly as I was also replacing
the AC powered fan with a low voltage DC one.
Modern PC PSUs have good EMI/RFI input circuits
that should cover any requirements for EMI/RFI
protection for the FDX.
filter stage from a typical ATX PSU
read the details of how it works