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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: Jose on June 30, 2004, 06:08:38 PM
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Got my A4000 assembled but the thing doesn't power on. It does make a low, repeated noise on the PSU, wich is exactly the same if I turn it on without having it connected to the motherboard... and the fan doesn't start in either case.
Does it need to be connected to the motherboard for the PSU fan to work? Cause if it doesn't I might have a broken PSU.
If it does, what could be the cause?
There's a connector on the motherboard that says key, but I think that only blocks the mouse and keyboard if used right? I also didn't coonect the power led but I'm pretty sure it's irrelevant...
I runned out of ideas and don't wanna end up blowing off the thing so, any suggestions really appreciated.
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There's a connector on the motherboard that says key, but I think that only blocks the mouse and keyboard if used right?
Correct. Open is normal usage, closed is keyboard and mouse locked.
Sounds like a bad power supply, to me. I never tried powering up an A4000 power supply with nothing attached, but I suspect the fan inside it should spin up. (The A3000 PS spins up the fan even with no other load, as do the old AT style ones [and even some ATX ones, provided you have it wired properly to start, at all].) And your A4000 supply certainly shouldn't be making a low-humming sound!
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I believe the power supply does have to be connected to the motherboard for the fan to come on... because the power supply itself won't work without a load. No power, no fan. But a bad fan can shut off the supply as well. The supply senses the current in the fan for stall or open. The ticking sound usually means the supply can't start. I'd suggest checking your drive cables to see if they're on backwards. Also check that all of the boards are seated correctly, and not offset in the slots which might short a supply.
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I've tried it without any drives connected too... Should start cause the motherboard and 3640 card would still be working, but the same happends....
:-(
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New info. I tried it also with just the flopy and the CDRom connected and the CD Rom light flashes along with those little kinda click sounds...
So I guess the motherboard is not at fault :-)
I still don't know what it is though :-(
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Well... it's possible that just the drives are not enough load for the power supply. Some of them won't start up without a load on the 5v. I had some problems with this when using old PC supplies to make external scsi boxes for the Amiga. I ended up using a dummy load on the 5v. Something to draw about an amp or so. That would be 5 ohms at at least 10 watts to be safe. If you feel inclined, this would be a better test of the power supply. It's still possible something on the motherboard is shorted out and loading the PS too much.
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@JimS
You were probably right!
I started disconnecting all drives with the mobo connected and it was the floppy drive that was badly connected! When I had removed all the drives (HD and CDROM) I had forgot to disconnect the floppy too...
Cheers
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By the way... this PSU, wich I think is pretty much a standard A4000 one, makes a lot of noise!! I was really disappointed...
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I was just working on an A4000D PSU before, and the fan does run with no other loads connected.
The PSU should be almost completely silent except for the fan noise (when it's running).
"PC" power supplies usually have a minimum load rating due to the way the voltage regulation works in them. It's a fairly crude and nasty circuit but works OK. A lot of them will power up with no load, but the open circuit voltage regulation will be poor. E.G. 6.2V instead of 5.0V or something.
The PSUs are fixable, but unless you're very familiar with switchmode power supplies, I wouldn't suggest poking around inside as you'll probably kill yourself! :shocked:
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Jose wrote:
@JimS
You were probably right!
I started disconnecting all drives with the mobo connected and it was the floppy drive that was badly connected! When I had removed all the drives (HD and CDROM) I had forgot to disconnect the floppy too...
Cheers
Cool.... you'll get that beast up and running now... :-)