I notice on the online manual for the 939 dual motherboard that there
are 2 power connectors:
4 pin ATX 12v power and 20 pin power connector.
Questions are:
Do I have to use the 4 pin connector (my power supply, 550W QTEC, does
not have such a connector
and what is this connector for please?
The square connector provides power for the processor. If
it is not plugged in, the motherboard cannot POST or even
beep. You need both the 2x2 square connector with the 12 volts
on it, and the 20 pin main connector, for a working system.
This is not the same thing as a 20+4 power connector. There
are some 24 pin power supplies, where the 24 pin part can
be split into two pieces (20+4). The purpose of that splitting,
is to allow plugging just the 20 pin portion into the main
power connector, without having to worry about bumping into
any adjacent caps. Many motherboards will allow the 20 pin
section of a 24 pin connector to be plugged in without bumping
into adjacent components, so it isn't essential that the
24 pin portion splits into two pieces.
The 2x2 ATX12V square connector is a different animal. It
has two yellow wires, carrying +12V. It has two ground wires
which are black. That is how you can tell you have the correct
one.
I don't know if any adapters are made, to make a 2x2 if it is
missing. A disk drive molex connector has one yellow wire,
and you would need two separate disk drive cables, to donate
their yellow wire to an adapter, to get decent current. Your
power supply should be rated for a minimum of 12V@15A, to even
think about powering a system with a 2x2 ATX12V connector.
With your new motherboard, you should treat yourself to a new
power supply. Page 36 of this document, shows some diagrams
of the connectors on the new supplies.
http://www.formfactors.org/developer/specs/ATX12V_PSDG_2_2_public_br2.pdf
To work out the rating for your new supply, you need to budget
for all the added components. Without a detailed list, it
is hard to be sure how much of a supply is needed. Generally,
the biggest concern is getting enough +12V, and that is
something that older supplies might not do. For example,
there was a Powmax a while back, that was a 500W supply, but
it only had 12V@10A, making the supply worthless for modern
computers having the square power connector.
Paul