I'm trying to fix a secondhand motherboard to my computer.
The existing psu has 12pins.
The new(secondhand) board has a 20 pin socket to accept power from the
psu. I've tried a couple of (actually 3) psu's borrowed from other
pc's and none of them work, ie the cooling fans do not spin when
connected to the power.
All of them work when back in their original computers.
Does the psu have to be fully connected before the cooling fans will
spin?

What's going on?

I've been trying to test the psu's before taking the pc apart and
connecting everything. Do I just have to bite the bullet?

Thanks in advance...

Cheers,
Mark,
M/cr

to reply by email, please take the michael

MarkD brought next idea :
I'm trying to fix a secondhand motherboard to my computer.
The existing psu has 12pins.
The new(secondhand) board has a 20 pin socket to accept power from the
psu. I've tried a couple of (actually 3) psu's borrowed from other
pc's and none of them work, ie the cooling fans do not spin when
connected to the power.
All of them work when back in their original computers.
Does the psu have to be fully connected before the cooling fans will
spin?

What's going on?

A Switch Mode Power Supply, which is what a typical PC power supply is,
needs some sort of load on it or it will shut itself down. An adequate
load would be something like a hard disk, plugged into one of the four
pin connectors. I'm not that familiar with the 20 pin jobs, so these
might well need something more, such as certain pins to be linked.

--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.org

In article , "MarkD"
says...
I'm trying to fix a secondhand motherboard to my computer.
The existing psu has 12pins.
The new(secondhand) board has a 20 pin socket to accept power from the
psu. I've tried a couple of (actually 3) psu's borrowed from other
pc's and none of them work, ie the cooling fans do not spin when
connected to the power.
All of them work when back in their original computers.
Does the psu have to be fully connected before the cooling fans will
spin?

12 pin is AT format, 20 pin is ATX. They're not really
interchangeable - you can get adaptors to plug them together, but the
case will need some modification or bodging as well.
Switch-mode PSUs will only work with at least a minimum load across
the output.
In ATX PCs the power is controlled by the motherboard - if it's not
fully hooked up you'll need to momentarily short out the pins that
would be connected to the switch on the front panel.

Ahhhh, that explains it....

....been driving me potty that one.

Thanks guys!

;-)

Cheers,
Mark,
M/cr

to reply by email, please take the michael
In article , "MarkD"
says...
I'm trying to fix a secondhand motherboard to my computer.
The existing psu has 12pins.
The new(secondhand) board has a 20 pin socket to accept power from the
psu. I've tried a couple of (actually 3) psu's borrowed from other
pc's and none of them work, ie the cooling fans do not spin when
connected to the power.
All of them work when back in their original computers.
Does the psu have to be fully connected before the cooling fans will
spin?

12 pin is AT format, 20 pin is ATX. They're not really
interchangeable - you can get adaptors to plug them together, but the
case will need some modification or bodging as well.
Switch-mode PSUs will only work with at least a minimum load across
the output.
In ATX PCs the power is controlled by the motherboard - if it's not
fully hooked up you'll need to momentarily short out the pins that
would be connected to the switch on the front panel.

"MarkD" wrote in message
...
I'm trying to fix a secondhand motherboard to my computer.
The existing psu has 12pins.

That sounds like an AT style motherboard, where you have a switch on the
front that will turn off the power supply via the mains side (Big CLICK
switch that you can see is on or off without it being plugged in (Or if it
is a push button type, you can feel it latch on or off)

The new(secondhand) board has a 20 pin socket to accept power from the
psu. I've tried a couple of (actually 3) psu's borrowed from other
pc's and none of them work, ie the cooling fans do not spin when
connected to the power.

This sounds like an ATX power supply, these work differently to AT ones.
On the motherboard, there should be two pins probably marked PWR SW or
something that will mean power switch - these need to be momentarily shorted
to get the power supply to turn on.



All of them work when back in their original computers.
Does the psu have to be fully connected before the cooling fans will
spin?

What's going on?

Or maybe the motherboard is faulty!?

Sparks...

SNIP...

Yes, I hadn't realised that the two styles of MoBo treated power
differently. What I hadn;t done is connect up all the hardware,
switches etc.
Momentarily short the power/switch pins eh?
Watch out for a smal mushroom cloud in the direction of Manchester....

This sounds like an ATX power supply, these work differently to AT ones.
On the motherboard, there should be two pins probably marked PWR SW or
something that will mean power switch - these need to be momentarily shorted
to get the power supply to turn on.

Or maybe the motherboard is faulty!?
I'm quite prepared for the Mobo to be faulty after all but what I
couldn;t work out is why none of the psu's were working.

Cheers,
Mark,
M/cr

to reply by email, please take the michael

"MarkD" wrote in message
...
I'm trying to fix a secondhand motherboard to my computer.
The existing psu has 12pins.
The new(secondhand) board has a 20 pin socket to accept power from the
psu. I've tried a couple of (actually 3) psu's borrowed from other
pc's and none of them work, ie the cooling fans do not spin when
connected to the power.
All of them work when back in their original computers.
Does the psu have to be fully connected before the cooling fans will
spin?

What's going on?

I've been trying to test the psu's before taking the pc apart and
connecting everything. Do I just have to bite the bullet?

Chuck the old PSU and buy one to ATX specs. Personally, I doubt that there
will be much, if anything, worth saving from the original machine. Even when
I absolutely *had* to use the case from an AT machine (the bloke I was
upgrading it for had had furniture specially built for it and nothing else
would fit) I ended up cutting a hole for a new fan as the cooling wasn't
good enough without.

Colin Bignell

SNIP...
Chuck the old PSU and buy one to ATX specs. Personally, I doubt that there
will be much, if anything, worth saving from the original machine. Even when
I absolutely *had* to use the case from an AT machine (the bloke I was
upgrading it for had had furniture specially built for it and nothing else
would fit) I ended up cutting a hole for a new fan as the cooling wasn't
good enough without.

the ones I have been trying are atx...and i'm very closwe to junking
the whole lot but the idea was to create a cheap second pc to use the
internet on with a cheap 20ukp wireless card installed.

The irony is the computer never worked properly in the first place.
TXPro2 motherboard that never recognised the wireless network card and
wouldn;t reinstall windows properly....hence the attempt at installing
a new board bought fresh from a computer fair....

Thanks again, all...

Cheers,
Mark,
M/cr

to reply by email, please take the michael

the ones I have been trying are atx...and i'm very closwe to junking
the whole lot but the idea was to create a cheap second pc to use the
internet on with a cheap 20ukp wireless card installed.

Holy crap is that all you wanted it for ? - check out www.itdealers.co.uk

--
Please add "[newsgroup]" in the subject of any personal replies via email
--- My new email address has "ngspamtrap" & @btinternet.com in it ;-) ---

Heh heh,
some good proces there....

Holy crap is that all you wanted it for ? - check out www.itdealers.co.uk

Cheers,
Mark,
M/cr

to reply by email, please take the michael

I'm trying to fix a secondhand motherboard to my computer.
The existing psu has 12pins.
The new(secondhand) board has a 20 pin socket to accept power from the
psu.

What make is the "new" board - Dell use proprietry PSU connectors, and
they often won`t work with "normal" power supplies.

--
Please add "[newsgroup]" in the subject of any personal replies via email
--- My new email address has "ngspamtrap" & @btinternet.com in it ;-) ---

"MarkD" wrote in message
...
I'm trying to fix a secondhand motherboard to my computer.
The existing psu has 12pins.
The new(secondhand) board has a 20 pin socket to accept power from the
psu. I've tried a couple of (actually 3) psu's borrowed from other
pc's and none of them work, ie the cooling fans do not spin when
connected to the power.
All of them work when back in their original computers.
Does the psu have to be fully connected before the cooling fans will
spin?

What's going on?

I've been trying to test the psu's before taking the pc apart and
connecting everything. Do I just have to bite the bullet?

Thanks in advance...

Cheers,
Mark,
M/cr

to reply by email, please take the michael

Traditionally, with PSU's, if you just connect mains power into them without
connecting the PSU's power leads to say the motherboard etc...then the PSU
will blow. It needs to dispel it's incoming power some where.

In article ,
"RedOnRed" writes:

Traditionally, with PSU's, if you just connect mains power into them without
connecting the PSU's power leads to say the motherboard etc...then the PSU
will blow. It needs to dispel it's incoming power some where.

Hum, I've done this tens, maybe hundreds of times, and never
had a PSU 'blow' in the process. A few AT PSU's will shut down
with no load, and most have poor regulation on the +12V and -12V
rails until you are drawing at least a few amps from the +5V,
but this doesn't harm the PSU (although if you have connected
something to those rails like a disk without drawing enough
load on the +5V rail, you might have problems with the disk
drive -- this was quite a common scenario).

ATX PSU's will just provide the low current 5V standby rail
if you plug them in with no motherboard connected. That's
effectively part of the ATX spec, as with the PS_ON pin
disconnected, the rest of the PSU will remain switched off.

--
Andrew Gabriel

"Andrew Gabriel" wrote in message
.. .
In article ,
"RedOnRed" writes:

Traditionally, with PSU's, if you just connect mains power into them
without
connecting the PSU's power leads to say the motherboard etc...then the
PSU
will blow. It needs to dispel it's incoming power some where.

Hum, I've done this tens, maybe hundreds of times, and never
had a PSU 'blow' in the process. A few AT PSU's will shut down

That surprises me, i've known quite a few (rookie) techies to do just what
you've been doing and not get away with it.


with no load, and most have poor regulation on the +12V and -12V
rails until you are drawing at least a few amps from the +5V,
but this doesn't harm the PSU (although if you have connected
something to those rails like a disk without drawing enough
load on the +5V rail, you might have problems with the disk
drive -- this was quite a common scenario).

ATX PSU's will just provide the low current 5V standby rail
if you plug them in with no motherboard connected. That's
effectively part of the ATX spec, as with the PS_ON pin
disconnected, the rest of the PSU will remain switched off.

--
Andrew Gabriel

"RedOnRed" wrote in
:


"MarkD" wrote in message
...
I'm trying to fix a secondhand motherboard to my computer.
The existing psu has 12pins.
The new(secondhand) board has a 20 pin socket to accept power
from the psu. I've tried a couple of (actually 3) psu's
borrowed from other pc's and none of them work, ie the cooling
fans do not spin when connected to the power.
All of them work when back in their original computers.
Does the psu have to be fully connected before the cooling fans
will spin?

What's going on?

I've been trying to test the psu's before taking the pc apart
and connecting everything. Do I just have to bite the bullet?

Thanks in advance...

Cheers,
Mark,
M/cr

to reply by email, please take the michael

Traditionally, with PSU's, if you just connect mains power into
them without connecting the PSU's power leads to say the
motherboard etc...then the PSU will blow. It needs to dispel
it's incoming power some where.



Nonsense.

In message , RedOnRed
writes

"MarkD" wrote in message
.. .
I'm trying to fix a secondhand motherboard to my computer.
The existing psu has 12pins.

Traditionally, with PSU's, if you just connect mains power into them without
connecting the PSU's power leads to say the motherboard etc...then the PSU
will blow. It needs to dispel it's incoming power some where.

What a complete load of toss


--
geoff

In article , raden
writes
In message , RedOnRed
writes

"MarkD" wrote in message
. ..
I'm trying to fix a secondhand motherboard to my computer.
The existing psu has 12pins.

Traditionally, with PSU's, if you just connect mains power into them without
connecting the PSU's power leads to say the motherboard etc...then the PSU
will blow. It needs to dispel it's incoming power some where.

What a complete load of toss



Lets have an explanation of the dissipates its incoming then
--
Tony Sayer

On Wed, 11 May 2005 22:08:37 UTC, tony sayer wrote:

In article , raden
writes
In message , RedOnRed
writes
Traditionally, with PSU's, if you just connect mains power into them without
connecting the PSU's power leads to say the motherboard etc...then the PSU
will blow. It needs to dispel it's incoming power some where.

What a complete load of toss

Lets have an explanation of the dissipates its incoming then

It generates invisible energy rays!

--
Bob Eager
begin a new life...dump Windows!

"Bob Eager" wrote in message
...
On Wed, 11 May 2005 22:08:37 UTC, tony sayer wrote:

In article , raden
writes
In message , RedOnRed
writes
Traditionally, with PSU's, if you just connect mains power into them
without
connecting the PSU's power leads to say the motherboard etc...then the
PSU
will blow. It needs to dispel it's incoming power some where.

What a complete load of toss

Lets have an explanation of the dissipates its incoming then

It generates invisible energy rays!

Bob Eager


Aaaaaarrrrrrgggghhhh!!!!! We're all going to die. I think my PSU is
dissipating through our floor. Or it could just be where the dog lies. But
something is causing this dissipation. No, it's OK, we're alright, it was
just wind. :-)

"Bob Eager" wrote in message
...

It generates invisible energy rays!

--
Bob Eager

Ah! That's what's making Steve's electricity meter turn.

--
LSR

MarkD wrote in
:

I'm trying to fix a secondhand motherboard to my computer.
The existing psu has 12pins.
The new(secondhand) board has a 20 pin socket to accept power
from the psu.

That suggests that the original PC, PSU and mobo are AT standard,
whereas the replacement PSU and mobo are ATX standard.

AT PCs had a conventional off/on mains switch on the front panel.

ATX PCs are powered into standby mode when connected to mains and use
a 'soft' power on switch that tells the mobo to tell the PSU to come
out of standby and start up. The power on switch needs to be a
momentary close that shorts a pair of contacts on the mobo.

Given the low price of PC cases, a replacement may be an easier
prospect than mackling the existing case.