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Ninehigh - 29/5/12 at 02:34 PM

This one is a headscratcher and a humdinger.

Following on from this thread, I have sourced a second hand graphics card, and motherboard with cpu, heatsink/fan and ram.

For further reference, this is the old board (go to page 18)

and this is the new board (go to page 28)

So I have to rewire the front panel jumper to the front panel connector, not a problem if somewhat fiddly. Put it all back together, plugged it in and it switched on. Then back off...

Normally I have to press the power button, so maybe I've done something that's shorting the two. But no, after some poking and prodding I have found that by bridging pins 2 and 3 on JP-F1 (new board) I can power up the board. I'm yet to connect the power and hdd led's but wtf is going on?

Btw I persume the auto powering down has something to do with the fan and heatsink not fitting properly, which I shall be poking at tomorrow

jamesbond007ltk - 29/5/12 at 02:49 PM

There is a very slim chance that the BIOS "After power fail" is set to on or similar so as soon as the board sees power it turns the computer on. Given that it is a new board and I have only ever seen this defaulted to off, I'd be surprised.

The front panel connector is an interesting one. Am I undertanding right that nothing is connected to JP-F1 when this "auto" on is happening?

If you bridge 1 & 2 does it turn on?

Does the board give you the polarity of pins 3 & 4 for the power LED?

I wonder if by bridging 2 & 3 you are closing effectively the same circuit as 1 & 2.

Still doesn't explain why it is turning it self on though!

Have you conencted the PC speaker (if it has one) or is there an onboard beeper? (Perhaps I should read that bit of the maunal before asking you). Do you get any warning tones prior to the power off? How long does it take?

Rich

Ninehigh - 29/5/12 at 03:07 PM

It does have an auto power on, but no idea what it's set to. The new board isn't "new out of the box" new, it's second hand so it could have been set like that.

Bridging pins 1 and 2 do nothing (although it should?)

It has a pc speaker somewhere, it gave me a long beep the first time before it powered off, and on further investigation I hadn't set the heatsink down properly (it's still not 100% so like I say I'll be poking at that tomorrow) and the power off is after about 3 or so seconds, in line with my previous experience of the cpu overheating problems.

What's getting me is that to switch it on I appear to have to connect the power switch negative and the power led positive!

jamesbond007ltk - 29/5/12 at 03:39 PM

quote:
Originally posted by Ninehigh
What's getting me is that to switch it on I appear to have to connect the power switch negative and the power led positive!

Putting 'any' positive voltage on the the neagtive pin of the power switch will turn the machine on, you are not completing a circuit but effectively raising the voltage on the ground pin.

What that doesn't explain is why the +ve on the LED is live when the machine is off, unless it is avery small voltage that is enough to raise the voltage on the ground pin? What voltage do you get between the power switch negative and the power led positive?

An alternative explanation would be that the Power LED has a switched ground.

It would appear that the power switch ground pin is fine but the positive is not. Do you get any voltage accross these pins?

Also, just another thing to check. Have you connected the 4-way power connector to the m/b? Sorry if I am teaching grandma here but I have left it off myself a good few times. It is normally yellow or yellow and black wires and labelled P4.

Sorry, not being too much help am I?

Rich

ETA: I assume your case switch is ATX and not the old clunk in and out type?

[Edited on 29/5/12 by jamesbond007ltk]

Ninehigh - 29/5/12 at 04:08 PM

Yeah everything's plugged into the board, and it's an atx one.

I don't have anything to test the voltage, but maybe the positive is faulty...

Also I have just noticed the power button has a light inside, it's usually green when on or yellow when on standby, and it's yellow now..