Finding -5V with M2-ATX PSU - Noob requests help please

**tazmaniandevil** · 05-11-2007, 08:26 AM

I need to install another mobo because I now have a Silabs USB radio which conflicts with the touch-screen no matter where I plug them in. I can have one or the other which is not much good really.
The board I have is an upgrade orphan, and not new. The board is an Asus P4B533-VM running a 2.4GHz CPU and 1Gb RAM. I can get everything working no problem indoors using a mains PSU, but when I plug it in to the M2-ATX PSU the fans spin, but I get "No VGA Signal" reported on the screen.
One of the chaps on the digital-car.co.uk forum thinks the board may need -5V which the M2-ATX does not supply.

My electronics knowledge is non-existent, so I don't know whether any -ve will do or if it needs to be corrected 5V via some kind of rectifier.

**NeoMatrixJR** · 05-11-2007, 09:36 AM

I can't be 100% certain on this, but when I looked it up, you should only need the -5V if your system has ISA card slots. Can someone else back this up?

**tazmaniandevil** · 05-11-2007, 02:24 PM

B0ll0x - back to square one then.

If I plug in a mains PSU, it all boots and runs like a dream. If I plug in the M2-ATX however, the fans spin, but all the screen says is "No VGA Signal" with no POST beeps etc.
The M2-ATX seems to be OK because it still powers the epia board OK.

**Sonicxtacy02** · 05-11-2007, 03:04 PM

Originally Posted by tazmaniandevil

B0ll0x - back to square one then.

If I plug in a mains PSU, it all boots and runs like a dream. If I plug in the M2-ATX however, the fans spin, but all the screen says is "No VGA Signal" with no POST beeps etc.
The M2-ATX seems to be OK because it still powers the epia board OK.

spins the fan with no POST and no beeps on an m2 usually means ur over its power limitation.. remove all your exteral stuff and try it

**tazmaniandevil** · 05-11-2007, 03:42 PM

I tried it with everything disconnected, even the hard disk. I used an online power calculator which came out at 114W. The M2-ATX should kick out 180W according to the manual. It is driving me nuts.

**Sonicxtacy02** · 05-11-2007, 03:51 PM

m2 is 160w... and while i'm thinkin about it.. do you have the p4 connector connected?

**MatrixPC** · 05-11-2007, 05:34 PM

you may be 114W but you "probably" overload one of the power rail.
-5V is use only if the system has ISA slot like neo already said.
Compare power rating on each rail of the desktop psu and see the different.
You can also try using the M2 to power just the mobo. And use the desktop PSU to power the HD/DVD to see if that work.

**Zeeshan0581** · 05-11-2007, 05:39 PM

This might be useful:
M2-ATX power distribution specs:
12V = 96W
3.3V = 26W
5V = 40W
Found this info on one of the power supplies thread, im sure if do a search you can find it.

**tazmaniandevil** · 05-11-2007, 06:42 PM

Originally Posted by MatrixPC

You can also try using the M2 to power just the mobo.

Thanx for all the suggestions folks - much appreciated. No ISA slots on this board, so I assume the -5V thing is not the problem. I do have the P4 connector connected, and have tested the outputs from the M2 and it all seems to be OK.
I tried the "mobo only" with the M2, but got the same result. The fekkin thing just won't fire up. It's a p1sser because I can't use the Silabs radio with the epia board.
The performance of the epia board otherwise is fine for my requirements..... I just want to use my Silabs radio so I can get rid of the head unit and the sh1tty cassette adapter.
If the M2-ATX is overloading, which was my first suspicion, I wish the board would power up on it's own because I read somewhere that you can use more than one M2-ATX in parallel.
The whole thing is driving me crazy.