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Dwight
19-11-2002, 02:46 PM
I have a Packard Bell machine purchased 5 years ago that I am trying to get going.

The problem I am having is that I have power to the motherboard, hard disk and cd etc but can't see anything on the monitor. I thought that maybe the onboard graphics is broken but it doesn't even seem to do the post test. It doesn't make the keyboard lights flash and it doesn't beep.

Could a very flat cmos battery cause this to happen. Do you have a suggestion

Thanks for your time

crozier
19-11-2002, 02:52 PM
I don't think a dud battery can cause this, it would simply revert to it's default settings and try to post. Can you try a pci or agp video card? Also try some different RAM

Dwight
19-11-2002, 02:59 PM
Yes I thought I might have to dig up an old pci card. But what suggestions do you have as to why the POST test isn't happening

Stormwarden
19-11-2002, 03:12 PM
I've had this problem a couple of times before in the past. Usually for me it's been because of something not quite plugged in correctly (like the CPU or RAM), or a jumper is connecting where it shouldn't, or a couple of jumper/connector pins have been bent and are touching.

another possiblity might be that the power supply's not up to scratch, and it's not giving a good "Power Good" signal or something along those lines. Some cheaper power supplies apparently generate a fake power good signal, which some motherboards don't seem to like. I'm not entirely sure on this however, someone please feel free to correct me if I'm wrong.

Dwight
19-11-2002, 03:21 PM
The power cables were all unplugged when I opened it so maybe I have left one off, I didn't think so though as it sounds right and all the lights are working. I will have a tinker and let you know how I get on tomorrow

thanks

crozier
19-11-2002, 03:26 PM
I'd do it this way:

Remove all pci / isa cards and all but one stick of RAM (but check that it's seated). Unplug all drives.
If you get something out of it (beeps or something) then add another perepheral or RAM until it won't POST.
If nothing then check the cables from the case panel and check the cpu is seated correctly.

Dwight
19-11-2002, 04:09 PM
Thanks for that, I never thought of trying it like that. I will let you know how I get on tomorrow

Billy T
19-11-2002, 10:33 PM
I looked into this some time ago when swapping a Compaq PSU into my generic box. Apart from the very short leads (sneaky) that I had to extend and two plugs for the main power connection to the MB where the original had only one it was a simple swap amd I didn't need the power good connection.

I looked into this at the time and it appears that fake "power good" is achieved by connecting the "power good" connection to a standard 5 volt output. That probably makes it a little more susceptible to boot power variations but in practice there doesn't seem to be any difference. Motherboards that don't like this arrangement are probably looking for a specific voltage rise time.

It doesn't seem terribly important to me but if any expert can help feel free to correct me. My installation works OK without it.

Cheers

Billy 8-{)

Graham L
20-11-2002, 12:49 PM
I think it's used to drive a NMI for "power going down", in cases where it's possible to get an orderly shutdown. It probably stops disk writing, etc. The signal "means" that all the supplies are up, and are stable.

In the PDP8, "Power Low" gave 1 mS warning ... plenty of time to save registers in core, and stop disks.

Billy T
21-11-2002, 01:43 PM
Hi Graham

That makes sense because if I recall correctly the "power good" source was relatively high impedance and would have dropped like a stone if the power sagged, while the filter caps might have held up and given the main voltage rails just a mS more time. It would also explain why some MBs won't work without it. They are permanently caught between rinse and spin. :^O

Cheers

Billy 8-{) :D