Quadra 700 only boots with HDD power disconnected

[Will]

Hi,

I'm having some problems with a Quadra 700. The Mac only (now) boots when the power to the HDD is disconnected, and goes straight into the flashing floppy screen.

When the HDD power is connected, the Mac does not boot at all - just a clicking sound comes from the machine. The PSU fan tries to spin too.

I assume this is some sort of problem with the power supply - possibly not being able to supply enough power? Weirdly the whole machine was working fine yesterday, although it hadn't been booted in a long while before that.

Is there something I can do to fix this? Has anyone experienced this before?

Thanks very much.

 

[uniserver]

yeah these hard drives in these vintage machines can go at any time... they are old and its just the name of the game when you collect vintage.

No worries though as if you check ebay there are SCSI 2 SD adaptors available now, and they offer you reliable service!

 

[Will]

yeah these hard drives in these vintage machines can go at any time... they are old and its just the name of the game when you collect vintage.

No worries though as if you check ebay there are SCSI 2 SD adaptors available now, and they offer you reliable service!

Really? Weird I've never heard of a dead HDD preventing a system from even booting (no chime or power light on the system) before!

 

[uniserver]

Yeah that is a strange one.  but some of these vintage hard drives have leaking electrolytic caps on the controller board.  and that those can cause all kinds of funny issues.

 

[CC_333]

Yeah, like a short that's causing the power supply's overload protection circuit to kick in. Perhaps this explains the periodic clicking you're hearing?

Anyway, I concur with Uniserver. Get a SCSI2SD. They're probably the best, most reliable hard drive-like device you can buy.

c

 

[Will]

Thanks so much for your help.

For anyone in the future - I can confirm that one of the molex power pins was shorted to ground, and therefore it must have been a shorted HDD causing the problem.

I might be able to try another molex device (newer HDD) in the machine at a later date, and will post back with results just to confirm.

 

[CelGen]

Yeah that is a strange one.  but some of these vintage hard drives have leaking electrolytic caps on the controller board.  and that those can cause all kinds of funny issues.

Screw lytics in this case. My money is on a shorted tant the power supply doesn't have enough of a kick to open on its own.

 

[Will]

Just tested with another drive and it seems to boot fine (in comparison to how it was). It definately was the original HDD causing the problem.

 

[uniserver]

calgen is right it could be a burnt up tantalum cap as they to burn up and go bad..

but not in the PSU though, in the hd controller....  Cal must be up there in hills of ca

drinking moonshine to keep warm.

 

[techknight]

The problem is a diode on your +12V or +5V molex connection, to ground has shorted. Common issue if the power supply spikes for some unknown reason. I have fixed a few that way. 

 

[uniserver]

I had a tantalum blow on a SATA seagate 320gig hard drive back in 07.