POP goes the ...

 ...47 ohm 3 amp current inrush device

A short post today. 

So, I had a major Code Brown moment with the Cifer. I have been trying to get the massive hard disks to give up their secrets to a BlueSCSI v2 but with little success. I've had great support from the creator but I have a sneaking suspicion that the Xebec controller board I'm using may be faulty.

Anyway, a couple of nights ago I tried again with the 10Mb Rodime unit that I have. No joy with initiator mode. I wondered if the drive itself might be the problem so I dug out the other unit. This one is a 20Mb monster but it makes enough noise to wake the dead when it's spinning up. The first video I took of switching on the Cifer, you can actually see me backing away from it as the howling starts...

To power the unit I'd been using the Cifer's power supply. A simple molex to the drive, then the regular  power connector to the IEEE488 HD board and a passthrough molex to the Xebec controller itself. Finally, another molex connector with an adaptor down to the correct connector for a floppy drive to power the BlueSCSI.

Preparing for action - those drive units are 
huge and inextricably heavy..

In this config, the Cifer still comes on but no peripherals are connected to the data buses. The IEEE488 card is just a power pass through and all other connections are direct to the power supply itself.

After carefully checking all the power connections and the config of the BlueSCSI I switched the power on. As expected, the Cifer's screen came on and the drive started to spin up. It got about a third of the way to the regular banshee scream but then faltered for a split second...

BANG!

The Cifer's screen went off, there was a massive blue flash from somewhere near the power supply followed by a cloud of magic smoke. I let out a whimper and punched the switch to 'off' at the power socket.

While checking myself for burn marks I realised that I hadn't tripped any circuits on my electrical panel (the lights in the work area were still on) and nothing was actually on fire. Phew!

But the smell of magic smoke was strong. What. Have. I. Done. 

There was nothing else for it but to dismantle the unit and get the power supply out again. And it didn't take long to find the issue.

Holy thermistor Batman!

Now call me old fashioned, but I don't think any component should have a hole in it accompanied by a grey smear on the nearby components. This is what you call a (magic) smoking gun. The component itself is a 47 ohm, 3 amp rated inrush thermistor - well it was before my hard disk decided to draw enough current to blow it to kingdom come. (The big resistor was already marked like that following a previous Rifa incident..)

It's a cheap and easy to obtain component, and two should be winging their way to me in the next few days. My hope is that if the hard disk drew enough current to cause a failure like that then it will have done its job and saved everything else. Fingers crossed...

I'm off to get some new underwear.