JP said:
Do older emachine computers take proprietary PSU?
I tried 5 different makes and none would work properly booting up the
machine. Finally ordered one from the emachines supplier and the machine
works perfectly. The old Bestec now becomes a spare.
Modern supplies no longer have a wire and pin for pin 18.
That used to be -5V.
You can download these, to get a table of wire colors and
voltages for the main connector. The first is back in a
time when the motherboard still had a connection to pin 18.
The other two are more modern versions. It is possible that
the five makes you tried, all are missing -5V.
20 pin with -5V
http://web.archive.org/web/20030424...org/developer/specs/atx/ATX_ATX12V_PS_1_1.pdf
20 pin without -5V (getting hard to find)
http://www.formfactors.org/developer/specs/atx/ATX12V_1_3dg.pdf
24 pin without -5V (what you can buy today)
http://www.formfactors.org/developer/specs/ATX12V_PSDG_2_2_public_br2.pdf
Note that, things like the Bestec may not adhere to the "standard"
color scheme. But if the pinout was standard, you'd notice
the same "pattern" to the connections. For example, where the
COM and +5V alternate on one side of the connector, you'd
expect to see the same color alternation on your Bestec.
All the +5V wires should be the same color, whatever color
they chose to use. So you should be able to correlate a bit,
even if you cannot be 100% certain of the pinout.
Since the replacement is working, you have a perfect opportunity
to verify the pinout. Many of the pins are rail voltages, and
only a few are logic signals. PWR_OK is a 5V level, when the
supply is working. PS_ON# is grounded or zero volts when
the supply is running. PS_ON# is 5V when the main outputs
are to be stopped. PS_ON# is driven by the motherboard.
PWR_OK is driven by the power supply.
The reason a supply won't run when sitting on your table
top, is PS_ON# needs to be grounded with a paper clip.
(COM is the same as ground or GND.) Of course, you have
to know which pin is PS_ON#. On a standard supply, it would
be pin 14 (of 20 pins).
To measure the power supply connector voltages, what I do
is clip the black lead of my multimeter to a ground screw on an
I/O connector on the back of the computer. By using an
alligator clip, that means I only need one hand to handle
the red probe. Set the multimeter on a scale high enough
to read the 12V or -12V rail. That would be 20V full scale
or 100V full scale, depending on the meter. Plug the red and
black leads, into the voltage measurement hole and the
common hole on the meter (not the amps measurement holes!).
If you accidentally attempt to measure using the amps hole
on the meter, the fuse will blow inside the meter.
You can probe where the wire enters the white nylon shroud
of the connector. There is enough exposed metal on the
crimped pin on each wire, to make contact and get a reading.
If you have an assistant standing near by, you can give them
a notepad and pen, to record what is shown on the multimeter
as you probe each pin.
You'll soon have established your own pinout for the main
connector.
My guess is it could be related to the missing -5V on pin 18
on the supplies that didn't work, but using your multimeter,
you'll soon know the truth.
The last multimeter I got, was $20 at the hardware store.
My "good" meter, if you could call it that, was slightly
more than $100, and includes fancy features such as
capacitance, frequency, and transistor Hfe (not much
call to measure Hfe any more). In this case, all you need
is the $20 version, as the measurement needed is
DC volts.
Paul
